Merge pull request #4630 from royAmmerschuber/pull-request/wildcard-provenance

initial implementation of wildcard provenence for tree borrows

Author: RalfJung

src/tools/miri/Cargo.toml

@@ -72,7 +72,7 @@ harness = false
 default = ["stack-cache", "native-lib"]
 genmc = ["dep:genmc-sys"]
 stack-cache = []
-stack-cache-consistency-check = ["stack-cache"]
+expensive-consistency-checks = ["stack-cache"]
 tracing = ["serde_json"]
 native-lib = ["dep:libffi", "dep:libloading", "dep:capstone", "dep:ipc-channel", "dep:nix", "dep:serde"]
 

src/tools/miri/src/bin/miri.rs

@@ -509,7 +509,6 @@ fn main() {
 Some(BorrowTrackerMethod::TreeBorrows(TreeBorrowsParams{
 precise_interior_mut:true,
 }));
- miri_config.provenance_mode = ProvenanceMode::Strict;
 }elseif arg == "-Zmiri-tree-borrows-no-precise-interior-mut"{
 match&mut miri_config.borrow_tracker{
 Some(BorrowTrackerMethod::TreeBorrows(params)) => {
@@ -703,17 +702,6 @@ fn main() {
  rustc_args.push(arg);
 }
 }
-// Tree Borrows implies strict provenance, and is not compatible with native calls.
-ifmatches!(miri_config.borrow_tracker,Some(BorrowTrackerMethod::TreeBorrows{ .. })){
-if miri_config.provenance_mode != ProvenanceMode::Strict{
-fatal_error!(
-"Tree Borrows does not support integer-to-pointer casts, and hence requires strict provenance"
-);
-}
-if !miri_config.native_lib.is_empty(){
-fatal_error!("Tree Borrows is not compatible with calling native functions");
-}
-}
 
 // Native calls and strict provenance are not compatible.
 if !miri_config.native_lib.is_empty() && miri_config.provenance_mode == ProvenanceMode::Strict{

src/tools/miri/src/borrow_tracker/mod.rs

@@ -352,6 +352,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 let borrow_tracker = this.machine.borrow_tracker.as_ref().unwrap();
 // The body of this loop needs `borrow_tracker` immutably
 // so we can't move this code inside the following `end_call`.
+
 for(alloc_id, tag)in&frame
 .extra
 .borrow_tracker
@@ -378,6 +379,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 }
 }
  borrow_tracker.borrow_mut().end_call(&frame.extra);
+
 interp_ok(())
 }
 }

src/tools/miri/src/borrow_tracker/stacked_borrows/stack.rs

@@ -153,7 +153,7 @@ impl<'tcx> Stack {
 /// Panics if any of the caching mechanisms have broken,
 /// - The StackCache indices don't refer to the parallel items,
 /// - There are no Unique items outside of first_unique..last_unique
-#[cfg(feature = "stack-cache-consistency-check")]
+#[cfg(feature = "expensive-consistency-checks")]
 fnverify_cache_consistency(&self){
 // Only a full cache needs to be valid. Also see the comments in find_granting_cache
 // and set_unknown_bottom.
@@ -197,7 +197,7 @@ impl<'tcx> Stack {
 tag:ProvenanceExtra,
 exposed_tags:&FxHashSet<BorTag>,
 ) -> Result<Option<usize>,()>{
-#[cfg(feature = "stack-cache-consistency-check")]
+#[cfg(feature = "expensive-consistency-checks")]
 self.verify_cache_consistency();
 
 letProvenanceExtra::Concrete(tag) = tag else{
@@ -334,7 +334,7 @@ impl<'tcx> Stack {
 // This primes the cache for the next access, which is almost always the just-added tag.
 self.cache.add(new_idx, new);
 
-#[cfg(feature = "stack-cache-consistency-check")]
+#[cfg(feature = "expensive-consistency-checks")]
 self.verify_cache_consistency();
 }
 
@@ -417,7 +417,7 @@ impl<'tcx> Stack {
 self.unique_range.end = self.unique_range.end.min(disable_start);
 }
 
-#[cfg(feature = "stack-cache-consistency-check")]
+#[cfg(feature = "expensive-consistency-checks")]
 self.verify_cache_consistency();
 
 interp_ok(())
@@ -472,7 +472,7 @@ impl<'tcx> Stack {
 self.unique_range = 0..0;
 }
 
-#[cfg(feature = "stack-cache-consistency-check")]
+#[cfg(feature = "expensive-consistency-checks")]
 self.verify_cache_consistency();
 interp_ok(())
 }

src/tools/miri/src/borrow_tracker/tree_borrows/diagnostics.rs

@@ -291,9 +291,10 @@ pub(super) struct TbError<'node> {
 pubconflicting_info:&'nodeNodeDebugInfo,
 // What kind of access caused this error (read, write, reborrow, deallocation)
 pubaccess_cause:AccessCause,
-/// Which tag the access that caused this error was made through, i.e.
+/// Which tag, if any, the access that caused this error was made through, i.e.
 /// which tag was used to read/write/deallocate.
-pubaccessed_info:&'nodeNodeDebugInfo,
+/// Not set on wildcard accesses.
+pubaccessed_info:Option<&'nodeNodeDebugInfo>,
 }
 
 implTbError<'_>{
@@ -302,10 +303,20 @@ impl TbError<'_> {
 useTransitionError::*;
 let cause = self.access_cause;
 let accessed = self.accessed_info;
+let accessed_str =
+self.accessed_info.map(|v| format!("{v}")).unwrap_or_else(|| "<wildcard>".into());
 let conflicting = self.conflicting_info;
-let accessed_is_conflicting = accessed.tag == conflicting.tag;
+// An access is considered conflicting if it happened through a
+// different tag than the one who caused UB.
+// When doing a wildcard access (where `accessed` is `None`) we
+// do not know which precise tag the accessed happened from,
+// however we can be certain that it did not come from the
+// conflicting tag.
+// This is because the wildcard data structure already removes
+// all tags through which an access would cause UB.
+let accessed_is_conflicting = accessed.map(|a| a.tag) == Some(conflicting.tag);
 let title = format!(
-"{cause} through {accessed} at {alloc_id:?}[{offset:#x}] is forbidden",
+"{cause} through {accessed_str} at {alloc_id:?}[{offset:#x}] is forbidden",
  alloc_id = self.alloc_id,
  offset = self.error_offset
 );
@@ -316,7 +327,7 @@ impl TbError<'_> {
 letmut details = Vec::new();
 if !accessed_is_conflicting {
  details.push(format!(
-"the accessed tag {accessed} is a child of the conflicting tag {conflicting}"
+"the accessed tag {accessed_str} is a child of the conflicting tag {conflicting}"
 ));
 }
 let access = cause.print_as_access(/* is_foreign */false);
@@ -330,7 +341,7 @@ impl TbError<'_> {
 let access = cause.print_as_access(/* is_foreign */true);
 let details = vec![
  format!(
-"the accessed tag {accessed} is foreign to the {conflicting_tag_name} tag {conflicting} (i.e., it is not a child)"
+"the accessed tag {accessed_str} is foreign to the {conflicting_tag_name} tag {conflicting} (i.e., it is not a child)"
 ),
  format!(
 "this {access} would cause the {conflicting_tag_name} tag {conflicting} (currently {before_disabled}) to become Disabled"
@@ -343,16 +354,18 @@ impl TbError<'_> {
 let conflicting_tag_name = "strongly protected";
 let details = vec![
  format!(
-"the allocation of the accessed tag {accessed} also contains the {conflicting_tag_name} tag {conflicting}"
+"the allocation of the accessed tag {accessed_str} also contains the {conflicting_tag_name} tag {conflicting}"
 ),
  format!("the {conflicting_tag_name} tag {conflicting} disallows deallocations"),
 ];
 (title, details, conflicting_tag_name)
 }
 };
 letmut history = HistoryData::default();
-if !accessed_is_conflicting {
- history.extend(self.accessed_info.history.forget(),"accessed",false);
+ifletSome(accessed_info) = self.accessed_info
+ && !accessed_is_conflicting
+{
+ history.extend(accessed_info.history.forget(),"accessed",false);
 }
  history.extend(
 self.conflicting_info.history.extract_relevant(self.error_offset,self.error_kind),
@@ -363,6 +376,20 @@ impl TbError<'_> {
 }
 }
 
+/// Cannot access this allocation with wildcard provenance, as there are no
+/// valid exposed references for this access kind.
+pubfnno_valid_exposed_references_error<'tcx>(
+alloc_id:AllocId,
+offset:u64,
+access_cause:AccessCause,
+) -> InterpErrorKind<'tcx>{
+let title =
+format!("{access_cause} through <wildcard> at {alloc_id:?}[{offset:#x}] is forbidden");
+let details = vec![format!("there are no exposed tags which may perform this access here")];
+let history = HistoryData::default();
+err_machine_stop!(TerminationInfo::TreeBorrowsUb{ title, details, history })
+}
+
 typeS = &'staticstr;
 /// Pretty-printing details
 ///
@@ -623,10 +650,10 @@ impl DisplayRepr {
 }else{
 // We take this node
 let rperm = tree
-.rperms
+.locations
 .iter_all()
-.map(move |(_offset,perms)| {
-let perm = perms.get(idx);
+.map(move |(_offset,loc)| {
+let perm = loc.perms.get(idx);
  perm.cloned()
 })
 .collect::<Vec<_>>();
@@ -788,7 +815,7 @@ impl<'tcx> Tree {
 show_unnamed:bool,
 ) -> InterpResult<'tcx>{
 letmut indenter = DisplayIndent::new();
-let ranges = self.rperms.iter_all().map(|(range,_perms)| range).collect::<Vec<_>>();
+let ranges = self.locations.iter_all().map(|(range,_loc)| range).collect::<Vec<_>>();
 ifletSome(repr) = DisplayRepr::from(self, show_unnamed){
  repr.print(
 &DEFAULT_FORMATTER,

src/tools/miri/src/borrow_tracker/tree_borrows/mod.rs

@@ -14,6 +14,7 @@ mod foreign_access_skipping;
 mod perms;
 mod tree;
 mod unimap;
+mod wildcard;
 
 #[cfg(test)]
 mod exhaustive;
@@ -54,16 +55,10 @@ impl<'tcx> Tree {
  interpret::Pointer::new(alloc_id, range.start),
  range.size.bytes(),
 );
-// TODO: for now we bail out on wildcard pointers. Eventually we should
-// handle them as much as we can.
-let tag = match prov {
-ProvenanceExtra::Concrete(tag) => tag,
-ProvenanceExtra::Wildcard => returninterp_ok(()),
-};
 let global = machine.borrow_tracker.as_ref().unwrap();
 let span = machine.current_user_relevant_span();
 self.perform_access(
-tag,
+prov,
 Some((range, access_kind, diagnostics::AccessCause::Explicit(access_kind))),
  global,
  alloc_id,
@@ -79,19 +74,9 @@ impl<'tcx> Tree {
 size:Size,
 machine:&MiriMachine<'tcx>,
 ) -> InterpResult<'tcx>{
-// TODO: for now we bail out on wildcard pointers. Eventually we should
-// handle them as much as we can.
-let tag = match prov {
-ProvenanceExtra::Concrete(tag) => tag,
-ProvenanceExtra::Wildcard => returninterp_ok(()),
-};
 let global = machine.borrow_tracker.as_ref().unwrap();
 let span = machine.current_user_relevant_span();
-self.dealloc(tag,alloc_range(Size::ZERO, size), global, alloc_id, span)
-}
-
-pubfnexpose_tag(&mutself,_tag:BorTag){
-// TODO
+self.dealloc(prov,alloc_range(Size::ZERO, size), global, alloc_id, span)
 }
 
 /// A tag just lost its protector.
@@ -109,7 +94,11 @@ impl<'tcx> Tree {
 ) -> InterpResult<'tcx>{
 let span = machine.current_user_relevant_span();
 // `None` makes it the magic on-protector-end operation
-self.perform_access(tag,None, global, alloc_id, span)
+self.perform_access(ProvenanceExtra::Concrete(tag),None, global, alloc_id, span)?;
+
+self.update_exposure_for_protector_release(tag);
+
+interp_ok(())
 }
 }
 
@@ -239,21 +228,22 @@ trait EvalContextPrivExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 assert_eq!(ptr_size,Size::ZERO);// we did the deref check above, size has to be 0 here
 // This pointer doesn't come with an AllocId, so there's no
 // memory to do retagging in.
+let new_prov = place.ptr().provenance;
 trace!(
-"reborrow of size 0: reference {:?} derived from {:?} (pointee {})",
- new_tag,
+"reborrow of size 0: reusing {:?} (pointee {})",
  place.ptr(),
  place.layout.ty,
 );
 log_creation(this,None)?;
 // Keep original provenance.
-returninterp_ok(place.ptr().provenance);
+returninterp_ok(new_prov);
 }
 };
+
 log_creation(this,Some((alloc_id, base_offset, parent_prov)))?;
 
 let orig_tag = match parent_prov {
-ProvenanceExtra::Wildcard => returninterp_ok(place.ptr().provenance),// TODO: handle wildcard pointers
+ProvenanceExtra::Wildcard => returninterp_ok(place.ptr().provenance),// TODO: handle retagging wildcard pointers
 ProvenanceExtra::Concrete(tag) => tag,
 };
 
@@ -356,7 +346,7 @@ trait EvalContextPrivExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 };
 
  tree_borrows.perform_access(
-orig_tag,
+parent_prov,
 Some((range_in_alloc,AccessKind::Read, diagnostics::AccessCause::Reborrow)),
  this.machine.borrow_tracker.as_ref().unwrap(),
  alloc_id,
@@ -589,7 +579,11 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 // uncovers a non-supported `extern static`.
 let alloc_extra = this.get_alloc_extra(alloc_id)?;
 trace!("Tree Borrows tag {tag:?} exposed in {alloc_id:?}");
- alloc_extra.borrow_tracker_tb().borrow_mut().expose_tag(tag);
+
+let global = this.machine.borrow_tracker.as_ref().unwrap();
+let protected_tags = &global.borrow().protected_tags;
+let protected = protected_tags.contains_key(&tag);
+ alloc_extra.borrow_tracker_tb().borrow_mut().expose_tag(tag, protected);
 }
 AllocKind::Function | AllocKind::VTable | AllocKind::TypeId | AllocKind::Dead => {
 // No tree borrows on these allocations.

src/tools/miri/src/borrow_tracker/tree_borrows/perms.rs

@@ -53,6 +53,7 @@ enum PermissionPriv {
 }
 useself::PermissionPriv::*;
 usesuper::foreign_access_skipping::IdempotentForeignAccess;
+usesuper::wildcard::WildcardAccessLevel;
 
 implPartialOrdforPermissionPriv{
 /// PermissionPriv is ordered by the reflexive transitive closure of
@@ -372,6 +373,23 @@ impl Permission {
 pubfnstrongest_idempotent_foreign_access(&self,prot:bool) -> IdempotentForeignAccess{
 self.inner.strongest_idempotent_foreign_access(prot)
 }
+
+/// Returns the strongest access allowed from a child to this node without
+/// causing UB (only considers possible transitions to this permission).
+pubfnstrongest_allowed_child_access(&self,protected:bool) -> WildcardAccessLevel{
+matchself.inner{
+// Everything except disabled can be accessed by read access.
+Disabled => WildcardAccessLevel::None,
+// Frozen references cannot be written to by a child.
+Frozen => WildcardAccessLevel::Read,
+// If the `conflicted` flag is set, then there was a foreign read
+// during the function call that is still ongoing (still `protected`),
+// this is UB (`noalias` violation).
+ReservedFrz{conflicted:true}if protected => WildcardAccessLevel::Read,
+// Everything else allows writes.
+ _ => WildcardAccessLevel::Write,
+}
+}
 }
 
 implPermTransition{
@@ -772,4 +790,32 @@ mod propagation_optimization_checks {
 );
 }
 }
+
+/// Checks that `strongest_allowed_child_access` correctly
+/// represents which transitions are possible.
+#[test]
+fnstrongest_allowed_child_access(){
+for(permission, protected)in <(Permission,bool)>::exhaustive(){
+let strongest_child_access = permission.strongest_allowed_child_access(protected);
+
+let is_read_valid = Permission::perform_access(
+AccessKind::Read,
+AccessRelatedness::LocalAccess,
+ permission,
+ protected,
+)
+.is_some();
+
+let is_write_valid = Permission::perform_access(
+AccessKind::Write,
+AccessRelatedness::LocalAccess,
+ permission,
+ protected,
+)
+.is_some();
+
+assert_eq!(is_read_valid, strongest_child_access >= WildcardAccessLevel::Read);
+assert_eq!(is_write_valid, strongest_child_access >= WildcardAccessLevel::Write);
+}
+}
 }

src/tools/miri/Cargo.toml

@@ -72,7 +72,7 @@ harness = false
 default = ["stack-cache", "native-lib"]
 genmc = ["dep:genmc-sys"]
 stack-cache = []
-stack-cache-consistency-check = ["stack-cache"]
+expensive-consistency-checks = ["stack-cache"]
 tracing = ["serde_json"]
 native-lib = ["dep:libffi", "dep:libloading", "dep:capstone", "dep:ipc-channel", "dep:nix", "dep:serde"]
 

src/tools/miri/src/bin/miri.rs

@@ -509,7 +509,6 @@ fn main() {
 Some(BorrowTrackerMethod::TreeBorrows(TreeBorrowsParams{
 precise_interior_mut:true,
 }));
- miri_config.provenance_mode = ProvenanceMode::Strict;
 }elseif arg == "-Zmiri-tree-borrows-no-precise-interior-mut"{
 match&mut miri_config.borrow_tracker{
 Some(BorrowTrackerMethod::TreeBorrows(params)) => {
@@ -703,17 +702,6 @@ fn main() {
  rustc_args.push(arg);
 }
 }
-// Tree Borrows implies strict provenance, and is not compatible with native calls.
-ifmatches!(miri_config.borrow_tracker,Some(BorrowTrackerMethod::TreeBorrows{ .. })){
-if miri_config.provenance_mode != ProvenanceMode::Strict{
-fatal_error!(
-"Tree Borrows does not support integer-to-pointer casts, and hence requires strict provenance"
-);
-}
-if !miri_config.native_lib.is_empty(){
-fatal_error!("Tree Borrows is not compatible with calling native functions");
-}
-}
 
 // Native calls and strict provenance are not compatible.
 if !miri_config.native_lib.is_empty() && miri_config.provenance_mode == ProvenanceMode::Strict{

src/tools/miri/src/borrow_tracker/mod.rs

@@ -352,6 +352,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 let borrow_tracker = this.machine.borrow_tracker.as_ref().unwrap();
 // The body of this loop needs `borrow_tracker` immutably
 // so we can't move this code inside the following `end_call`.
+
 for(alloc_id, tag)in&frame
 .extra
 .borrow_tracker
@@ -378,6 +379,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 }
 }
  borrow_tracker.borrow_mut().end_call(&frame.extra);
+
 interp_ok(())
 }
 }

src/tools/miri/src/borrow_tracker/stacked_borrows/stack.rs

@@ -153,7 +153,7 @@ impl<'tcx> Stack {
 /// Panics if any of the caching mechanisms have broken,
 /// - The StackCache indices don't refer to the parallel items,
 /// - There are no Unique items outside of first_unique..last_unique
-#[cfg(feature = "stack-cache-consistency-check")]
+#[cfg(feature = "expensive-consistency-checks")]
 fnverify_cache_consistency(&self){
 // Only a full cache needs to be valid. Also see the comments in find_granting_cache
 // and set_unknown_bottom.
@@ -197,7 +197,7 @@ impl<'tcx> Stack {
 tag:ProvenanceExtra,
 exposed_tags:&FxHashSet<BorTag>,
 ) -> Result<Option<usize>,()>{
-#[cfg(feature = "stack-cache-consistency-check")]
+#[cfg(feature = "expensive-consistency-checks")]
 self.verify_cache_consistency();
 
 letProvenanceExtra::Concrete(tag) = tag else{
@@ -334,7 +334,7 @@ impl<'tcx> Stack {
 // This primes the cache for the next access, which is almost always the just-added tag.
 self.cache.add(new_idx, new);
 
-#[cfg(feature = "stack-cache-consistency-check")]
+#[cfg(feature = "expensive-consistency-checks")]
 self.verify_cache_consistency();
 }
 
@@ -417,7 +417,7 @@ impl<'tcx> Stack {
 self.unique_range.end = self.unique_range.end.min(disable_start);
 }
 
-#[cfg(feature = "stack-cache-consistency-check")]
+#[cfg(feature = "expensive-consistency-checks")]
 self.verify_cache_consistency();
 
 interp_ok(())
@@ -472,7 +472,7 @@ impl<'tcx> Stack {
 self.unique_range = 0..0;
 }
 
-#[cfg(feature = "stack-cache-consistency-check")]
+#[cfg(feature = "expensive-consistency-checks")]
 self.verify_cache_consistency();
 interp_ok(())
 }

src/tools/miri/src/borrow_tracker/tree_borrows/diagnostics.rs

@@ -291,9 +291,10 @@ pub(super) struct TbError<'node> {
 pubconflicting_info:&'nodeNodeDebugInfo,
 // What kind of access caused this error (read, write, reborrow, deallocation)
 pubaccess_cause:AccessCause,
-/// Which tag the access that caused this error was made through, i.e.
+/// Which tag, if any, the access that caused this error was made through, i.e.
 /// which tag was used to read/write/deallocate.
-pubaccessed_info:&'nodeNodeDebugInfo,
+/// Not set on wildcard accesses.
+pubaccessed_info:Option<&'nodeNodeDebugInfo>,
 }
 
 implTbError<'_>{
@@ -302,10 +303,20 @@ impl TbError<'_> {
 useTransitionError::*;
 let cause = self.access_cause;
 let accessed = self.accessed_info;
+let accessed_str =
+self.accessed_info.map(|v| format!("{v}")).unwrap_or_else(|| "<wildcard>".into());
 let conflicting = self.conflicting_info;
-let accessed_is_conflicting = accessed.tag == conflicting.tag;
+// An access is considered conflicting if it happened through a
+// different tag than the one who caused UB.
+// When doing a wildcard access (where `accessed` is `None`) we
+// do not know which precise tag the accessed happened from,
+// however we can be certain that it did not come from the
+// conflicting tag.
+// This is because the wildcard data structure already removes
+// all tags through which an access would cause UB.
+let accessed_is_conflicting = accessed.map(|a| a.tag) == Some(conflicting.tag);
 let title = format!(
-"{cause} through {accessed} at {alloc_id:?}[{offset:#x}] is forbidden",
+"{cause} through {accessed_str} at {alloc_id:?}[{offset:#x}] is forbidden",
  alloc_id = self.alloc_id,
  offset = self.error_offset
 );
@@ -316,7 +327,7 @@ impl TbError<'_> {
 letmut details = Vec::new();
 if !accessed_is_conflicting {
  details.push(format!(
-"the accessed tag {accessed} is a child of the conflicting tag {conflicting}"
+"the accessed tag {accessed_str} is a child of the conflicting tag {conflicting}"
 ));
 }
 let access = cause.print_as_access(/* is_foreign */false);
@@ -330,7 +341,7 @@ impl TbError<'_> {
 let access = cause.print_as_access(/* is_foreign */true);
 let details = vec![
  format!(
-"the accessed tag {accessed} is foreign to the {conflicting_tag_name} tag {conflicting} (i.e., it is not a child)"
+"the accessed tag {accessed_str} is foreign to the {conflicting_tag_name} tag {conflicting} (i.e., it is not a child)"
 ),
  format!(
 "this {access} would cause the {conflicting_tag_name} tag {conflicting} (currently {before_disabled}) to become Disabled"
@@ -343,16 +354,18 @@ impl TbError<'_> {
 let conflicting_tag_name = "strongly protected";
 let details = vec![
  format!(
-"the allocation of the accessed tag {accessed} also contains the {conflicting_tag_name} tag {conflicting}"
+"the allocation of the accessed tag {accessed_str} also contains the {conflicting_tag_name} tag {conflicting}"
 ),
  format!("the {conflicting_tag_name} tag {conflicting} disallows deallocations"),
 ];
 (title, details, conflicting_tag_name)
 }
 };
 letmut history = HistoryData::default();
-if !accessed_is_conflicting {
- history.extend(self.accessed_info.history.forget(),"accessed",false);
+ifletSome(accessed_info) = self.accessed_info
+ && !accessed_is_conflicting
+{
+ history.extend(accessed_info.history.forget(),"accessed",false);
 }
  history.extend(
 self.conflicting_info.history.extract_relevant(self.error_offset,self.error_kind),
@@ -363,6 +376,20 @@ impl TbError<'_> {
 }
 }
 
+/// Cannot access this allocation with wildcard provenance, as there are no
+/// valid exposed references for this access kind.
+pubfnno_valid_exposed_references_error<'tcx>(
+alloc_id:AllocId,
+offset:u64,
+access_cause:AccessCause,
+) -> InterpErrorKind<'tcx>{
+let title =
+format!("{access_cause} through <wildcard> at {alloc_id:?}[{offset:#x}] is forbidden");
+let details = vec![format!("there are no exposed tags which may perform this access here")];
+let history = HistoryData::default();
+err_machine_stop!(TerminationInfo::TreeBorrowsUb{ title, details, history })
+}
+
 typeS = &'staticstr;
 /// Pretty-printing details
 ///
@@ -623,10 +650,10 @@ impl DisplayRepr {
 }else{
 // We take this node
 let rperm = tree
-.rperms
+.locations
 .iter_all()
-.map(move |(_offset,perms)| {
-let perm = perms.get(idx);
+.map(move |(_offset,loc)| {
+let perm = loc.perms.get(idx);
  perm.cloned()
 })
 .collect::<Vec<_>>();
@@ -788,7 +815,7 @@ impl<'tcx> Tree {
 show_unnamed:bool,
 ) -> InterpResult<'tcx>{
 letmut indenter = DisplayIndent::new();
-let ranges = self.rperms.iter_all().map(|(range,_perms)| range).collect::<Vec<_>>();
+let ranges = self.locations.iter_all().map(|(range,_loc)| range).collect::<Vec<_>>();
 ifletSome(repr) = DisplayRepr::from(self, show_unnamed){
  repr.print(
 &DEFAULT_FORMATTER,

src/tools/miri/src/borrow_tracker/tree_borrows/mod.rs

@@ -14,6 +14,7 @@ mod foreign_access_skipping;
 mod perms;
 mod tree;
 mod unimap;
+mod wildcard;
 
 #[cfg(test)]
 mod exhaustive;
@@ -54,16 +55,10 @@ impl<'tcx> Tree {
  interpret::Pointer::new(alloc_id, range.start),
  range.size.bytes(),
 );
-// TODO: for now we bail out on wildcard pointers. Eventually we should
-// handle them as much as we can.
-let tag = match prov {
-ProvenanceExtra::Concrete(tag) => tag,
-ProvenanceExtra::Wildcard => returninterp_ok(()),
-};
 let global = machine.borrow_tracker.as_ref().unwrap();
 let span = machine.current_user_relevant_span();
 self.perform_access(
-tag,
+prov,
 Some((range, access_kind, diagnostics::AccessCause::Explicit(access_kind))),
  global,
  alloc_id,
@@ -79,19 +74,9 @@ impl<'tcx> Tree {
 size:Size,
 machine:&MiriMachine<'tcx>,
 ) -> InterpResult<'tcx>{
-// TODO: for now we bail out on wildcard pointers. Eventually we should
-// handle them as much as we can.
-let tag = match prov {
-ProvenanceExtra::Concrete(tag) => tag,
-ProvenanceExtra::Wildcard => returninterp_ok(()),
-};
 let global = machine.borrow_tracker.as_ref().unwrap();
 let span = machine.current_user_relevant_span();
-self.dealloc(tag,alloc_range(Size::ZERO, size), global, alloc_id, span)
-}
-
-pubfnexpose_tag(&mutself,_tag:BorTag){
-// TODO
+self.dealloc(prov,alloc_range(Size::ZERO, size), global, alloc_id, span)
 }
 
 /// A tag just lost its protector.
@@ -109,7 +94,11 @@ impl<'tcx> Tree {
 ) -> InterpResult<'tcx>{
 let span = machine.current_user_relevant_span();
 // `None` makes it the magic on-protector-end operation
-self.perform_access(tag,None, global, alloc_id, span)
+self.perform_access(ProvenanceExtra::Concrete(tag),None, global, alloc_id, span)?;
+
+self.update_exposure_for_protector_release(tag);
+
+interp_ok(())
 }
 }
 
@@ -239,21 +228,22 @@ trait EvalContextPrivExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 assert_eq!(ptr_size,Size::ZERO);// we did the deref check above, size has to be 0 here
 // This pointer doesn't come with an AllocId, so there's no
 // memory to do retagging in.
+let new_prov = place.ptr().provenance;
 trace!(
-"reborrow of size 0: reference {:?} derived from {:?} (pointee {})",
- new_tag,
+"reborrow of size 0: reusing {:?} (pointee {})",
  place.ptr(),
  place.layout.ty,
 );
 log_creation(this,None)?;
 // Keep original provenance.
-returninterp_ok(place.ptr().provenance);
+returninterp_ok(new_prov);
 }
 };
+
 log_creation(this,Some((alloc_id, base_offset, parent_prov)))?;
 
 let orig_tag = match parent_prov {
-ProvenanceExtra::Wildcard => returninterp_ok(place.ptr().provenance),// TODO: handle wildcard pointers
+ProvenanceExtra::Wildcard => returninterp_ok(place.ptr().provenance),// TODO: handle retagging wildcard pointers
 ProvenanceExtra::Concrete(tag) => tag,
 };
 
@@ -356,7 +346,7 @@ trait EvalContextPrivExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 };
 
  tree_borrows.perform_access(
-orig_tag,
+parent_prov,
 Some((range_in_alloc,AccessKind::Read, diagnostics::AccessCause::Reborrow)),
  this.machine.borrow_tracker.as_ref().unwrap(),
  alloc_id,
@@ -589,7 +579,11 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 // uncovers a non-supported `extern static`.
 let alloc_extra = this.get_alloc_extra(alloc_id)?;
 trace!("Tree Borrows tag {tag:?} exposed in {alloc_id:?}");
- alloc_extra.borrow_tracker_tb().borrow_mut().expose_tag(tag);
+
+let global = this.machine.borrow_tracker.as_ref().unwrap();
+let protected_tags = &global.borrow().protected_tags;
+let protected = protected_tags.contains_key(&tag);
+ alloc_extra.borrow_tracker_tb().borrow_mut().expose_tag(tag, protected);
 }
 AllocKind::Function | AllocKind::VTable | AllocKind::TypeId | AllocKind::Dead => {
 // No tree borrows on these allocations.

src/tools/miri/src/borrow_tracker/tree_borrows/perms.rs

@@ -53,6 +53,7 @@ enum PermissionPriv {
 }
 useself::PermissionPriv::*;
 usesuper::foreign_access_skipping::IdempotentForeignAccess;
+usesuper::wildcard::WildcardAccessLevel;
 
 implPartialOrdforPermissionPriv{
 /// PermissionPriv is ordered by the reflexive transitive closure of
@@ -372,6 +373,23 @@ impl Permission {
 pubfnstrongest_idempotent_foreign_access(&self,prot:bool) -> IdempotentForeignAccess{
 self.inner.strongest_idempotent_foreign_access(prot)
 }
+
+/// Returns the strongest access allowed from a child to this node without
+/// causing UB (only considers possible transitions to this permission).
+pubfnstrongest_allowed_child_access(&self,protected:bool) -> WildcardAccessLevel{
+matchself.inner{
+// Everything except disabled can be accessed by read access.
+Disabled => WildcardAccessLevel::None,
+// Frozen references cannot be written to by a child.
+Frozen => WildcardAccessLevel::Read,
+// If the `conflicted` flag is set, then there was a foreign read
+// during the function call that is still ongoing (still `protected`),
+// this is UB (`noalias` violation).
+ReservedFrz{conflicted:true}if protected => WildcardAccessLevel::Read,
+// Everything else allows writes.
+ _ => WildcardAccessLevel::Write,
+}
+}
 }
 
 implPermTransition{
@@ -772,4 +790,32 @@ mod propagation_optimization_checks {
 );
 }
 }
+
+/// Checks that `strongest_allowed_child_access` correctly
+/// represents which transitions are possible.
+#[test]
+fnstrongest_allowed_child_access(){
+for(permission, protected)in <(Permission,bool)>::exhaustive(){
+let strongest_child_access = permission.strongest_allowed_child_access(protected);
+
+let is_read_valid = Permission::perform_access(
+AccessKind::Read,
+AccessRelatedness::LocalAccess,
+ permission,
+ protected,
+)
+.is_some();
+
+let is_write_valid = Permission::perform_access(
+AccessKind::Write,
+AccessRelatedness::LocalAccess,
+ permission,
+ protected,
+)
+.is_some();
+
+assert_eq!(is_read_valid, strongest_child_access >= WildcardAccessLevel::Read);
+assert_eq!(is_write_valid, strongest_child_access >= WildcardAccessLevel::Write);
+}
+}
 }

src/tools/miri/Cargo.toml

@@ -72,7 +72,7 @@ harness = false
 default = ["stack-cache", "native-lib"]
 genmc = ["dep:genmc-sys"]
 stack-cache = []
-stack-cache-consistency-check = ["stack-cache"]
+expensive-consistency-checks = ["stack-cache"]
 tracing = ["serde_json"]
 native-lib = ["dep:libffi", "dep:libloading", "dep:capstone", "dep:ipc-channel", "dep:nix", "dep:serde"]
 

src/tools/miri/src/bin/miri.rs

@@ -509,7 +509,6 @@ fn main() {
 Some(BorrowTrackerMethod::TreeBorrows(TreeBorrowsParams{
 precise_interior_mut:true,
 }));
- miri_config.provenance_mode = ProvenanceMode::Strict;
 }elseif arg == "-Zmiri-tree-borrows-no-precise-interior-mut"{
 match&mut miri_config.borrow_tracker{
 Some(BorrowTrackerMethod::TreeBorrows(params)) => {
@@ -703,17 +702,6 @@ fn main() {
  rustc_args.push(arg);
 }
 }
-// Tree Borrows implies strict provenance, and is not compatible with native calls.
-ifmatches!(miri_config.borrow_tracker,Some(BorrowTrackerMethod::TreeBorrows{ .. })){
-if miri_config.provenance_mode != ProvenanceMode::Strict{
-fatal_error!(
-"Tree Borrows does not support integer-to-pointer casts, and hence requires strict provenance"
-);
-}
-if !miri_config.native_lib.is_empty(){
-fatal_error!("Tree Borrows is not compatible with calling native functions");
-}
-}
 
 // Native calls and strict provenance are not compatible.
 if !miri_config.native_lib.is_empty() && miri_config.provenance_mode == ProvenanceMode::Strict{

src/tools/miri/src/borrow_tracker/mod.rs

@@ -352,6 +352,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 let borrow_tracker = this.machine.borrow_tracker.as_ref().unwrap();
 // The body of this loop needs `borrow_tracker` immutably
 // so we can't move this code inside the following `end_call`.
+
 for(alloc_id, tag)in&frame
 .extra
 .borrow_tracker
@@ -378,6 +379,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 }
 }
  borrow_tracker.borrow_mut().end_call(&frame.extra);
+
 interp_ok(())
 }
 }

src/tools/miri/src/borrow_tracker/stacked_borrows/stack.rs

@@ -153,7 +153,7 @@ impl<'tcx> Stack {
 /// Panics if any of the caching mechanisms have broken,
 /// - The StackCache indices don't refer to the parallel items,
 /// - There are no Unique items outside of first_unique..last_unique
-#[cfg(feature = "stack-cache-consistency-check")]
+#[cfg(feature = "expensive-consistency-checks")]
 fnverify_cache_consistency(&self){
 // Only a full cache needs to be valid. Also see the comments in find_granting_cache
 // and set_unknown_bottom.
@@ -197,7 +197,7 @@ impl<'tcx> Stack {
 tag:ProvenanceExtra,
 exposed_tags:&FxHashSet<BorTag>,
 ) -> Result<Option<usize>,()>{
-#[cfg(feature = "stack-cache-consistency-check")]
+#[cfg(feature = "expensive-consistency-checks")]
 self.verify_cache_consistency();
 
 letProvenanceExtra::Concrete(tag) = tag else{
@@ -334,7 +334,7 @@ impl<'tcx> Stack {
 // This primes the cache for the next access, which is almost always the just-added tag.
 self.cache.add(new_idx, new);
 
-#[cfg(feature = "stack-cache-consistency-check")]
+#[cfg(feature = "expensive-consistency-checks")]
 self.verify_cache_consistency();
 }
 
@@ -417,7 +417,7 @@ impl<'tcx> Stack {
 self.unique_range.end = self.unique_range.end.min(disable_start);
 }
 
-#[cfg(feature = "stack-cache-consistency-check")]
+#[cfg(feature = "expensive-consistency-checks")]
 self.verify_cache_consistency();
 
 interp_ok(())
@@ -472,7 +472,7 @@ impl<'tcx> Stack {
 self.unique_range = 0..0;
 }
 
-#[cfg(feature = "stack-cache-consistency-check")]
+#[cfg(feature = "expensive-consistency-checks")]
 self.verify_cache_consistency();
 interp_ok(())
 }

src/tools/miri/src/borrow_tracker/tree_borrows/diagnostics.rs

@@ -291,9 +291,10 @@ pub(super) struct TbError<'node> {
 pubconflicting_info:&'nodeNodeDebugInfo,
 // What kind of access caused this error (read, write, reborrow, deallocation)
 pubaccess_cause:AccessCause,
-/// Which tag the access that caused this error was made through, i.e.
+/// Which tag, if any, the access that caused this error was made through, i.e.
 /// which tag was used to read/write/deallocate.
-pubaccessed_info:&'nodeNodeDebugInfo,
+/// Not set on wildcard accesses.
+pubaccessed_info:Option<&'nodeNodeDebugInfo>,
 }
 
 implTbError<'_>{
@@ -302,10 +303,20 @@ impl TbError<'_> {
 useTransitionError::*;
 let cause = self.access_cause;
 let accessed = self.accessed_info;
+let accessed_str =
+self.accessed_info.map(|v| format!("{v}")).unwrap_or_else(|| "<wildcard>".into());
 let conflicting = self.conflicting_info;
-let accessed_is_conflicting = accessed.tag == conflicting.tag;
+// An access is considered conflicting if it happened through a
+// different tag than the one who caused UB.
+// When doing a wildcard access (where `accessed` is `None`) we
+// do not know which precise tag the accessed happened from,
+// however we can be certain that it did not come from the
+// conflicting tag.
+// This is because the wildcard data structure already removes
+// all tags through which an access would cause UB.
+let accessed_is_conflicting = accessed.map(|a| a.tag) == Some(conflicting.tag);
 let title = format!(
-"{cause} through {accessed} at {alloc_id:?}[{offset:#x}] is forbidden",
+"{cause} through {accessed_str} at {alloc_id:?}[{offset:#x}] is forbidden",
  alloc_id = self.alloc_id,
  offset = self.error_offset
 );
@@ -316,7 +327,7 @@ impl TbError<'_> {
 letmut details = Vec::new();
 if !accessed_is_conflicting {
  details.push(format!(
-"the accessed tag {accessed} is a child of the conflicting tag {conflicting}"
+"the accessed tag {accessed_str} is a child of the conflicting tag {conflicting}"
 ));
 }
 let access = cause.print_as_access(/* is_foreign */false);
@@ -330,7 +341,7 @@ impl TbError<'_> {
 let access = cause.print_as_access(/* is_foreign */true);
 let details = vec![
  format!(
-"the accessed tag {accessed} is foreign to the {conflicting_tag_name} tag {conflicting} (i.e., it is not a child)"
+"the accessed tag {accessed_str} is foreign to the {conflicting_tag_name} tag {conflicting} (i.e., it is not a child)"
 ),
  format!(
 "this {access} would cause the {conflicting_tag_name} tag {conflicting} (currently {before_disabled}) to become Disabled"
@@ -343,16 +354,18 @@ impl TbError<'_> {
 let conflicting_tag_name = "strongly protected";
 let details = vec![
  format!(
-"the allocation of the accessed tag {accessed} also contains the {conflicting_tag_name} tag {conflicting}"
+"the allocation of the accessed tag {accessed_str} also contains the {conflicting_tag_name} tag {conflicting}"
 ),
  format!("the {conflicting_tag_name} tag {conflicting} disallows deallocations"),
 ];
 (title, details, conflicting_tag_name)
 }
 };
 letmut history = HistoryData::default();
-if !accessed_is_conflicting {
- history.extend(self.accessed_info.history.forget(),"accessed",false);
+ifletSome(accessed_info) = self.accessed_info
+ && !accessed_is_conflicting
+{
+ history.extend(accessed_info.history.forget(),"accessed",false);
 }
  history.extend(
 self.conflicting_info.history.extract_relevant(self.error_offset,self.error_kind),
@@ -363,6 +376,20 @@ impl TbError<'_> {
 }
 }
 
+/// Cannot access this allocation with wildcard provenance, as there are no
+/// valid exposed references for this access kind.
+pubfnno_valid_exposed_references_error<'tcx>(
+alloc_id:AllocId,
+offset:u64,
+access_cause:AccessCause,
+) -> InterpErrorKind<'tcx>{
+let title =
+format!("{access_cause} through <wildcard> at {alloc_id:?}[{offset:#x}] is forbidden");
+let details = vec![format!("there are no exposed tags which may perform this access here")];
+let history = HistoryData::default();
+err_machine_stop!(TerminationInfo::TreeBorrowsUb{ title, details, history })
+}
+
 typeS = &'staticstr;
 /// Pretty-printing details
 ///
@@ -623,10 +650,10 @@ impl DisplayRepr {
 }else{
 // We take this node
 let rperm = tree
-.rperms
+.locations
 .iter_all()
-.map(move |(_offset,perms)| {
-let perm = perms.get(idx);
+.map(move |(_offset,loc)| {
+let perm = loc.perms.get(idx);
  perm.cloned()
 })
 .collect::<Vec<_>>();
@@ -788,7 +815,7 @@ impl<'tcx> Tree {
 show_unnamed:bool,
 ) -> InterpResult<'tcx>{
 letmut indenter = DisplayIndent::new();
-let ranges = self.rperms.iter_all().map(|(range,_perms)| range).collect::<Vec<_>>();
+let ranges = self.locations.iter_all().map(|(range,_loc)| range).collect::<Vec<_>>();
 ifletSome(repr) = DisplayRepr::from(self, show_unnamed){
  repr.print(
 &DEFAULT_FORMATTER,

src/tools/miri/src/borrow_tracker/tree_borrows/mod.rs

@@ -14,6 +14,7 @@ mod foreign_access_skipping;
 mod perms;
 mod tree;
 mod unimap;
+mod wildcard;
 
 #[cfg(test)]
 mod exhaustive;
@@ -54,16 +55,10 @@ impl<'tcx> Tree {
  interpret::Pointer::new(alloc_id, range.start),
  range.size.bytes(),
 );
-// TODO: for now we bail out on wildcard pointers. Eventually we should
-// handle them as much as we can.
-let tag = match prov {
-ProvenanceExtra::Concrete(tag) => tag,
-ProvenanceExtra::Wildcard => returninterp_ok(()),
-};
 let global = machine.borrow_tracker.as_ref().unwrap();
 let span = machine.current_user_relevant_span();
 self.perform_access(
-tag,
+prov,
 Some((range, access_kind, diagnostics::AccessCause::Explicit(access_kind))),
  global,
  alloc_id,
@@ -79,19 +74,9 @@ impl<'tcx> Tree {
 size:Size,
 machine:&MiriMachine<'tcx>,
 ) -> InterpResult<'tcx>{
-// TODO: for now we bail out on wildcard pointers. Eventually we should
-// handle them as much as we can.
-let tag = match prov {
-ProvenanceExtra::Concrete(tag) => tag,
-ProvenanceExtra::Wildcard => returninterp_ok(()),
-};
 let global = machine.borrow_tracker.as_ref().unwrap();
 let span = machine.current_user_relevant_span();
-self.dealloc(tag,alloc_range(Size::ZERO, size), global, alloc_id, span)
-}
-
-pubfnexpose_tag(&mutself,_tag:BorTag){
-// TODO
+self.dealloc(prov,alloc_range(Size::ZERO, size), global, alloc_id, span)
 }
 
 /// A tag just lost its protector.
@@ -109,7 +94,11 @@ impl<'tcx> Tree {
 ) -> InterpResult<'tcx>{
 let span = machine.current_user_relevant_span();
 // `None` makes it the magic on-protector-end operation
-self.perform_access(tag,None, global, alloc_id, span)
+self.perform_access(ProvenanceExtra::Concrete(tag),None, global, alloc_id, span)?;
+
+self.update_exposure_for_protector_release(tag);
+
+interp_ok(())
 }
 }
 
@@ -239,21 +228,22 @@ trait EvalContextPrivExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 assert_eq!(ptr_size,Size::ZERO);// we did the deref check above, size has to be 0 here
 // This pointer doesn't come with an AllocId, so there's no
 // memory to do retagging in.
+let new_prov = place.ptr().provenance;
 trace!(
-"reborrow of size 0: reference {:?} derived from {:?} (pointee {})",
- new_tag,
+"reborrow of size 0: reusing {:?} (pointee {})",
  place.ptr(),
  place.layout.ty,
 );
 log_creation(this,None)?;
 // Keep original provenance.
-returninterp_ok(place.ptr().provenance);
+returninterp_ok(new_prov);
 }
 };
+
 log_creation(this,Some((alloc_id, base_offset, parent_prov)))?;
 
 let orig_tag = match parent_prov {
-ProvenanceExtra::Wildcard => returninterp_ok(place.ptr().provenance),// TODO: handle wildcard pointers
+ProvenanceExtra::Wildcard => returninterp_ok(place.ptr().provenance),// TODO: handle retagging wildcard pointers
 ProvenanceExtra::Concrete(tag) => tag,
 };
 
@@ -356,7 +346,7 @@ trait EvalContextPrivExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 };
 
  tree_borrows.perform_access(
-orig_tag,
+parent_prov,
 Some((range_in_alloc,AccessKind::Read, diagnostics::AccessCause::Reborrow)),
  this.machine.borrow_tracker.as_ref().unwrap(),
  alloc_id,
@@ -589,7 +579,11 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 // uncovers a non-supported `extern static`.
 let alloc_extra = this.get_alloc_extra(alloc_id)?;
 trace!("Tree Borrows tag {tag:?} exposed in {alloc_id:?}");
- alloc_extra.borrow_tracker_tb().borrow_mut().expose_tag(tag);
+
+let global = this.machine.borrow_tracker.as_ref().unwrap();
+let protected_tags = &global.borrow().protected_tags;
+let protected = protected_tags.contains_key(&tag);
+ alloc_extra.borrow_tracker_tb().borrow_mut().expose_tag(tag, protected);
 }
 AllocKind::Function | AllocKind::VTable | AllocKind::TypeId | AllocKind::Dead => {
 // No tree borrows on these allocations.

src/tools/miri/src/borrow_tracker/tree_borrows/perms.rs

@@ -53,6 +53,7 @@ enum PermissionPriv {
 }
 useself::PermissionPriv::*;
 usesuper::foreign_access_skipping::IdempotentForeignAccess;
+usesuper::wildcard::WildcardAccessLevel;
 
 implPartialOrdforPermissionPriv{
 /// PermissionPriv is ordered by the reflexive transitive closure of
@@ -372,6 +373,23 @@ impl Permission {
 pubfnstrongest_idempotent_foreign_access(&self,prot:bool) -> IdempotentForeignAccess{
 self.inner.strongest_idempotent_foreign_access(prot)
 }
+
+/// Returns the strongest access allowed from a child to this node without
+/// causing UB (only considers possible transitions to this permission).
+pubfnstrongest_allowed_child_access(&self,protected:bool) -> WildcardAccessLevel{
+matchself.inner{
+// Everything except disabled can be accessed by read access.
+Disabled => WildcardAccessLevel::None,
+// Frozen references cannot be written to by a child.
+Frozen => WildcardAccessLevel::Read,
+// If the `conflicted` flag is set, then there was a foreign read
+// during the function call that is still ongoing (still `protected`),
+// this is UB (`noalias` violation).
+ReservedFrz{conflicted:true}if protected => WildcardAccessLevel::Read,
+// Everything else allows writes.
+ _ => WildcardAccessLevel::Write,
+}
+}
 }
 
 implPermTransition{
@@ -772,4 +790,32 @@ mod propagation_optimization_checks {
 );
 }
 }
+
+/// Checks that `strongest_allowed_child_access` correctly
+/// represents which transitions are possible.
+#[test]
+fnstrongest_allowed_child_access(){
+for(permission, protected)in <(Permission,bool)>::exhaustive(){
+let strongest_child_access = permission.strongest_allowed_child_access(protected);
+
+let is_read_valid = Permission::perform_access(
+AccessKind::Read,
+AccessRelatedness::LocalAccess,
+ permission,
+ protected,
+)
+.is_some();
+
+let is_write_valid = Permission::perform_access(
+AccessKind::Write,
+AccessRelatedness::LocalAccess,
+ permission,
+ protected,
+)
+.is_some();
+
+assert_eq!(is_read_valid, strongest_child_access >= WildcardAccessLevel::Read);
+assert_eq!(is_write_valid, strongest_child_access >= WildcardAccessLevel::Write);
+}
+}
 }

src/tools/miri/Cargo.toml

@@ -72,7 +72,7 @@ harness = false
 default = ["stack-cache", "native-lib"]
 genmc = ["dep:genmc-sys"]
 stack-cache = []
-stack-cache-consistency-check = ["stack-cache"]
+expensive-consistency-checks = ["stack-cache"]
 tracing = ["serde_json"]
 native-lib = ["dep:libffi", "dep:libloading", "dep:capstone", "dep:ipc-channel", "dep:nix", "dep:serde"]
 

src/tools/miri/src/bin/miri.rs

@@ -509,7 +509,6 @@ fn main() {
 Some(BorrowTrackerMethod::TreeBorrows(TreeBorrowsParams{
 precise_interior_mut:true,
 }));
- miri_config.provenance_mode = ProvenanceMode::Strict;
 }elseif arg == "-Zmiri-tree-borrows-no-precise-interior-mut"{
 match&mut miri_config.borrow_tracker{
 Some(BorrowTrackerMethod::TreeBorrows(params)) => {
@@ -703,17 +702,6 @@ fn main() {
  rustc_args.push(arg);
 }
 }
-// Tree Borrows implies strict provenance, and is not compatible with native calls.
-ifmatches!(miri_config.borrow_tracker,Some(BorrowTrackerMethod::TreeBorrows{ .. })){
-if miri_config.provenance_mode != ProvenanceMode::Strict{
-fatal_error!(
-"Tree Borrows does not support integer-to-pointer casts, and hence requires strict provenance"
-);
-}
-if !miri_config.native_lib.is_empty(){
-fatal_error!("Tree Borrows is not compatible with calling native functions");
-}
-}
 
 // Native calls and strict provenance are not compatible.
 if !miri_config.native_lib.is_empty() && miri_config.provenance_mode == ProvenanceMode::Strict{

src/tools/miri/src/borrow_tracker/mod.rs

@@ -352,6 +352,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 let borrow_tracker = this.machine.borrow_tracker.as_ref().unwrap();
 // The body of this loop needs `borrow_tracker` immutably
 // so we can't move this code inside the following `end_call`.
+
 for(alloc_id, tag)in&frame
 .extra
 .borrow_tracker
@@ -378,6 +379,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 }
 }
  borrow_tracker.borrow_mut().end_call(&frame.extra);
+
 interp_ok(())
 }
 }

src/tools/miri/src/borrow_tracker/stacked_borrows/stack.rs

@@ -153,7 +153,7 @@ impl<'tcx> Stack {
 /// Panics if any of the caching mechanisms have broken,
 /// - The StackCache indices don't refer to the parallel items,
 /// - There are no Unique items outside of first_unique..last_unique
-#[cfg(feature = "stack-cache-consistency-check")]
+#[cfg(feature = "expensive-consistency-checks")]
 fnverify_cache_consistency(&self){
 // Only a full cache needs to be valid. Also see the comments in find_granting_cache
 // and set_unknown_bottom.
@@ -197,7 +197,7 @@ impl<'tcx> Stack {
 tag:ProvenanceExtra,
 exposed_tags:&FxHashSet<BorTag>,
 ) -> Result<Option<usize>,()>{
-#[cfg(feature = "stack-cache-consistency-check")]
+#[cfg(feature = "expensive-consistency-checks")]
 self.verify_cache_consistency();
 
 letProvenanceExtra::Concrete(tag) = tag else{
@@ -334,7 +334,7 @@ impl<'tcx> Stack {
 // This primes the cache for the next access, which is almost always the just-added tag.
 self.cache.add(new_idx, new);
 
-#[cfg(feature = "stack-cache-consistency-check")]
+#[cfg(feature = "expensive-consistency-checks")]
 self.verify_cache_consistency();
 }
 
@@ -417,7 +417,7 @@ impl<'tcx> Stack {
 self.unique_range.end = self.unique_range.end.min(disable_start);
 }
 
-#[cfg(feature = "stack-cache-consistency-check")]
+#[cfg(feature = "expensive-consistency-checks")]
 self.verify_cache_consistency();
 
 interp_ok(())
@@ -472,7 +472,7 @@ impl<'tcx> Stack {
 self.unique_range = 0..0;
 }
 
-#[cfg(feature = "stack-cache-consistency-check")]
+#[cfg(feature = "expensive-consistency-checks")]
 self.verify_cache_consistency();
 interp_ok(())
 }

src/tools/miri/src/borrow_tracker/tree_borrows/diagnostics.rs

@@ -291,9 +291,10 @@ pub(super) struct TbError<'node> {
 pubconflicting_info:&'nodeNodeDebugInfo,
 // What kind of access caused this error (read, write, reborrow, deallocation)
 pubaccess_cause:AccessCause,
-/// Which tag the access that caused this error was made through, i.e.
+/// Which tag, if any, the access that caused this error was made through, i.e.
 /// which tag was used to read/write/deallocate.
-pubaccessed_info:&'nodeNodeDebugInfo,
+/// Not set on wildcard accesses.
+pubaccessed_info:Option<&'nodeNodeDebugInfo>,
 }
 
 implTbError<'_>{
@@ -302,10 +303,20 @@ impl TbError<'_> {
 useTransitionError::*;
 let cause = self.access_cause;
 let accessed = self.accessed_info;
+let accessed_str =
+self.accessed_info.map(|v| format!("{v}")).unwrap_or_else(|| "<wildcard>".into());
 let conflicting = self.conflicting_info;
-let accessed_is_conflicting = accessed.tag == conflicting.tag;
+// An access is considered conflicting if it happened through a
+// different tag than the one who caused UB.
+// When doing a wildcard access (where `accessed` is `None`) we
+// do not know which precise tag the accessed happened from,
+// however we can be certain that it did not come from the
+// conflicting tag.
+// This is because the wildcard data structure already removes
+// all tags through which an access would cause UB.
+let accessed_is_conflicting = accessed.map(|a| a.tag) == Some(conflicting.tag);
 let title = format!(
-"{cause} through {accessed} at {alloc_id:?}[{offset:#x}] is forbidden",
+"{cause} through {accessed_str} at {alloc_id:?}[{offset:#x}] is forbidden",
  alloc_id = self.alloc_id,
  offset = self.error_offset
 );
@@ -316,7 +327,7 @@ impl TbError<'_> {
 letmut details = Vec::new();
 if !accessed_is_conflicting {
  details.push(format!(
-"the accessed tag {accessed} is a child of the conflicting tag {conflicting}"
+"the accessed tag {accessed_str} is a child of the conflicting tag {conflicting}"
 ));
 }
 let access = cause.print_as_access(/* is_foreign */false);
@@ -330,7 +341,7 @@ impl TbError<'_> {
 let access = cause.print_as_access(/* is_foreign */true);
 let details = vec![
  format!(
-"the accessed tag {accessed} is foreign to the {conflicting_tag_name} tag {conflicting} (i.e., it is not a child)"
+"the accessed tag {accessed_str} is foreign to the {conflicting_tag_name} tag {conflicting} (i.e., it is not a child)"
 ),
  format!(
 "this {access} would cause the {conflicting_tag_name} tag {conflicting} (currently {before_disabled}) to become Disabled"
@@ -343,16 +354,18 @@ impl TbError<'_> {
 let conflicting_tag_name = "strongly protected";
 let details = vec![
  format!(
-"the allocation of the accessed tag {accessed} also contains the {conflicting_tag_name} tag {conflicting}"
+"the allocation of the accessed tag {accessed_str} also contains the {conflicting_tag_name} tag {conflicting}"
 ),
  format!("the {conflicting_tag_name} tag {conflicting} disallows deallocations"),
 ];
 (title, details, conflicting_tag_name)
 }
 };
 letmut history = HistoryData::default();
-if !accessed_is_conflicting {
- history.extend(self.accessed_info.history.forget(),"accessed",false);
+ifletSome(accessed_info) = self.accessed_info
+ && !accessed_is_conflicting
+{
+ history.extend(accessed_info.history.forget(),"accessed",false);
 }
  history.extend(
 self.conflicting_info.history.extract_relevant(self.error_offset,self.error_kind),
@@ -363,6 +376,20 @@ impl TbError<'_> {
 }
 }
 
+/// Cannot access this allocation with wildcard provenance, as there are no
+/// valid exposed references for this access kind.
+pubfnno_valid_exposed_references_error<'tcx>(
+alloc_id:AllocId,
+offset:u64,
+access_cause:AccessCause,
+) -> InterpErrorKind<'tcx>{
+let title =
+format!("{access_cause} through <wildcard> at {alloc_id:?}[{offset:#x}] is forbidden");
+let details = vec![format!("there are no exposed tags which may perform this access here")];
+let history = HistoryData::default();
+err_machine_stop!(TerminationInfo::TreeBorrowsUb{ title, details, history })
+}
+
 typeS = &'staticstr;
 /// Pretty-printing details
 ///
@@ -623,10 +650,10 @@ impl DisplayRepr {
 }else{
 // We take this node
 let rperm = tree
-.rperms
+.locations
 .iter_all()
-.map(move |(_offset,perms)| {
-let perm = perms.get(idx);
+.map(move |(_offset,loc)| {
+let perm = loc.perms.get(idx);
  perm.cloned()
 })
 .collect::<Vec<_>>();
@@ -788,7 +815,7 @@ impl<'tcx> Tree {
 show_unnamed:bool,
 ) -> InterpResult<'tcx>{
 letmut indenter = DisplayIndent::new();
-let ranges = self.rperms.iter_all().map(|(range,_perms)| range).collect::<Vec<_>>();
+let ranges = self.locations.iter_all().map(|(range,_loc)| range).collect::<Vec<_>>();
 ifletSome(repr) = DisplayRepr::from(self, show_unnamed){
  repr.print(
 &DEFAULT_FORMATTER,

src/tools/miri/src/borrow_tracker/tree_borrows/mod.rs

@@ -14,6 +14,7 @@ mod foreign_access_skipping;
 mod perms;
 mod tree;
 mod unimap;
+mod wildcard;
 
 #[cfg(test)]
 mod exhaustive;
@@ -54,16 +55,10 @@ impl<'tcx> Tree {
  interpret::Pointer::new(alloc_id, range.start),
  range.size.bytes(),
 );
-// TODO: for now we bail out on wildcard pointers. Eventually we should
-// handle them as much as we can.
-let tag = match prov {
-ProvenanceExtra::Concrete(tag) => tag,
-ProvenanceExtra::Wildcard => returninterp_ok(()),
-};
 let global = machine.borrow_tracker.as_ref().unwrap();
 let span = machine.current_user_relevant_span();
 self.perform_access(
-tag,
+prov,
 Some((range, access_kind, diagnostics::AccessCause::Explicit(access_kind))),
  global,
  alloc_id,
@@ -79,19 +74,9 @@ impl<'tcx> Tree {
 size:Size,
 machine:&MiriMachine<'tcx>,
 ) -> InterpResult<'tcx>{
-// TODO: for now we bail out on wildcard pointers. Eventually we should
-// handle them as much as we can.
-let tag = match prov {
-ProvenanceExtra::Concrete(tag) => tag,
-ProvenanceExtra::Wildcard => returninterp_ok(()),
-};
 let global = machine.borrow_tracker.as_ref().unwrap();
 let span = machine.current_user_relevant_span();
-self.dealloc(tag,alloc_range(Size::ZERO, size), global, alloc_id, span)
-}
-
-pubfnexpose_tag(&mutself,_tag:BorTag){
-// TODO
+self.dealloc(prov,alloc_range(Size::ZERO, size), global, alloc_id, span)
 }
 
 /// A tag just lost its protector.
@@ -109,7 +94,11 @@ impl<'tcx> Tree {
 ) -> InterpResult<'tcx>{
 let span = machine.current_user_relevant_span();
 // `None` makes it the magic on-protector-end operation
-self.perform_access(tag,None, global, alloc_id, span)
+self.perform_access(ProvenanceExtra::Concrete(tag),None, global, alloc_id, span)?;
+
+self.update_exposure_for_protector_release(tag);
+
+interp_ok(())
 }
 }
 
@@ -239,21 +228,22 @@ trait EvalContextPrivExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 assert_eq!(ptr_size,Size::ZERO);// we did the deref check above, size has to be 0 here
 // This pointer doesn't come with an AllocId, so there's no
 // memory to do retagging in.
+let new_prov = place.ptr().provenance;
 trace!(
-"reborrow of size 0: reference {:?} derived from {:?} (pointee {})",
- new_tag,
+"reborrow of size 0: reusing {:?} (pointee {})",
  place.ptr(),
  place.layout.ty,
 );
 log_creation(this,None)?;
 // Keep original provenance.
-returninterp_ok(place.ptr().provenance);
+returninterp_ok(new_prov);
 }
 };
+
 log_creation(this,Some((alloc_id, base_offset, parent_prov)))?;
 
 let orig_tag = match parent_prov {
-ProvenanceExtra::Wildcard => returninterp_ok(place.ptr().provenance),// TODO: handle wildcard pointers
+ProvenanceExtra::Wildcard => returninterp_ok(place.ptr().provenance),// TODO: handle retagging wildcard pointers
 ProvenanceExtra::Concrete(tag) => tag,
 };
 
@@ -356,7 +346,7 @@ trait EvalContextPrivExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 };
 
  tree_borrows.perform_access(
-orig_tag,
+parent_prov,
 Some((range_in_alloc,AccessKind::Read, diagnostics::AccessCause::Reborrow)),
  this.machine.borrow_tracker.as_ref().unwrap(),
  alloc_id,
@@ -589,7 +579,11 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 // uncovers a non-supported `extern static`.
 let alloc_extra = this.get_alloc_extra(alloc_id)?;
 trace!("Tree Borrows tag {tag:?} exposed in {alloc_id:?}");
- alloc_extra.borrow_tracker_tb().borrow_mut().expose_tag(tag);
+
+let global = this.machine.borrow_tracker.as_ref().unwrap();
+let protected_tags = &global.borrow().protected_tags;
+let protected = protected_tags.contains_key(&tag);
+ alloc_extra.borrow_tracker_tb().borrow_mut().expose_tag(tag, protected);
 }
 AllocKind::Function | AllocKind::VTable | AllocKind::TypeId | AllocKind::Dead => {
 // No tree borrows on these allocations.

src/tools/miri/src/borrow_tracker/tree_borrows/perms.rs

@@ -53,6 +53,7 @@ enum PermissionPriv {
 }
 useself::PermissionPriv::*;
 usesuper::foreign_access_skipping::IdempotentForeignAccess;
+usesuper::wildcard::WildcardAccessLevel;
 
 implPartialOrdforPermissionPriv{
 /// PermissionPriv is ordered by the reflexive transitive closure of
@@ -372,6 +373,23 @@ impl Permission {
 pubfnstrongest_idempotent_foreign_access(&self,prot:bool) -> IdempotentForeignAccess{
 self.inner.strongest_idempotent_foreign_access(prot)
 }
+
+/// Returns the strongest access allowed from a child to this node without
+/// causing UB (only considers possible transitions to this permission).
+pubfnstrongest_allowed_child_access(&self,protected:bool) -> WildcardAccessLevel{
+matchself.inner{
+// Everything except disabled can be accessed by read access.
+Disabled => WildcardAccessLevel::None,
+// Frozen references cannot be written to by a child.
+Frozen => WildcardAccessLevel::Read,
+// If the `conflicted` flag is set, then there was a foreign read
+// during the function call that is still ongoing (still `protected`),
+// this is UB (`noalias` violation).
+ReservedFrz{conflicted:true}if protected => WildcardAccessLevel::Read,
+// Everything else allows writes.
+ _ => WildcardAccessLevel::Write,
+}
+}
 }
 
 implPermTransition{
@@ -772,4 +790,32 @@ mod propagation_optimization_checks {
 );
 }
 }
+
+/// Checks that `strongest_allowed_child_access` correctly
+/// represents which transitions are possible.
+#[test]
+fnstrongest_allowed_child_access(){
+for(permission, protected)in <(Permission,bool)>::exhaustive(){
+let strongest_child_access = permission.strongest_allowed_child_access(protected);
+
+let is_read_valid = Permission::perform_access(
+AccessKind::Read,
+AccessRelatedness::LocalAccess,
+ permission,
+ protected,
+)
+.is_some();
+
+let is_write_valid = Permission::perform_access(
+AccessKind::Write,
+AccessRelatedness::LocalAccess,
+ permission,
+ protected,
+)
+.is_some();
+
+assert_eq!(is_read_valid, strongest_child_access >= WildcardAccessLevel::Read);
+assert_eq!(is_write_valid, strongest_child_access >= WildcardAccessLevel::Write);
+}
+}
 }

src/tools/miri/Cargo.toml

@@ -72,7 +72,7 @@ harness = false
 default = ["stack-cache", "native-lib"]
 genmc = ["dep:genmc-sys"]
 stack-cache = []
-stack-cache-consistency-check = ["stack-cache"]
+expensive-consistency-checks = ["stack-cache"]
 tracing = ["serde_json"]
 native-lib = ["dep:libffi", "dep:libloading", "dep:capstone", "dep:ipc-channel", "dep:nix", "dep:serde"]
 

src/tools/miri/src/bin/miri.rs

@@ -509,7 +509,6 @@ fn main() {
 Some(BorrowTrackerMethod::TreeBorrows(TreeBorrowsParams{
 precise_interior_mut:true,
 }));
- miri_config.provenance_mode = ProvenanceMode::Strict;
 }elseif arg == "-Zmiri-tree-borrows-no-precise-interior-mut"{
 match&mut miri_config.borrow_tracker{
 Some(BorrowTrackerMethod::TreeBorrows(params)) => {
@@ -703,17 +702,6 @@ fn main() {
  rustc_args.push(arg);
 }
 }
-// Tree Borrows implies strict provenance, and is not compatible with native calls.
-ifmatches!(miri_config.borrow_tracker,Some(BorrowTrackerMethod::TreeBorrows{ .. })){
-if miri_config.provenance_mode != ProvenanceMode::Strict{
-fatal_error!(
-"Tree Borrows does not support integer-to-pointer casts, and hence requires strict provenance"
-);
-}
-if !miri_config.native_lib.is_empty(){
-fatal_error!("Tree Borrows is not compatible with calling native functions");
-}
-}
 
 // Native calls and strict provenance are not compatible.
 if !miri_config.native_lib.is_empty() && miri_config.provenance_mode == ProvenanceMode::Strict{

src/tools/miri/src/borrow_tracker/mod.rs

@@ -352,6 +352,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 let borrow_tracker = this.machine.borrow_tracker.as_ref().unwrap();
 // The body of this loop needs `borrow_tracker` immutably
 // so we can't move this code inside the following `end_call`.
+
 for(alloc_id, tag)in&frame
 .extra
 .borrow_tracker
@@ -378,6 +379,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 }
 }
  borrow_tracker.borrow_mut().end_call(&frame.extra);
+
 interp_ok(())
 }
 }

src/tools/miri/src/borrow_tracker/stacked_borrows/stack.rs

@@ -153,7 +153,7 @@ impl<'tcx> Stack {
 /// Panics if any of the caching mechanisms have broken,
 /// - The StackCache indices don't refer to the parallel items,
 /// - There are no Unique items outside of first_unique..last_unique
-#[cfg(feature = "stack-cache-consistency-check")]
+#[cfg(feature = "expensive-consistency-checks")]
 fnverify_cache_consistency(&self){
 // Only a full cache needs to be valid. Also see the comments in find_granting_cache
 // and set_unknown_bottom.
@@ -197,7 +197,7 @@ impl<'tcx> Stack {
 tag:ProvenanceExtra,
 exposed_tags:&FxHashSet<BorTag>,
 ) -> Result<Option<usize>,()>{
-#[cfg(feature = "stack-cache-consistency-check")]
+#[cfg(feature = "expensive-consistency-checks")]
 self.verify_cache_consistency();
 
 letProvenanceExtra::Concrete(tag) = tag else{
@@ -334,7 +334,7 @@ impl<'tcx> Stack {
 // This primes the cache for the next access, which is almost always the just-added tag.
 self.cache.add(new_idx, new);
 
-#[cfg(feature = "stack-cache-consistency-check")]
+#[cfg(feature = "expensive-consistency-checks")]
 self.verify_cache_consistency();
 }
 
@@ -417,7 +417,7 @@ impl<'tcx> Stack {
 self.unique_range.end = self.unique_range.end.min(disable_start);
 }
 
-#[cfg(feature = "stack-cache-consistency-check")]
+#[cfg(feature = "expensive-consistency-checks")]
 self.verify_cache_consistency();
 
 interp_ok(())
@@ -472,7 +472,7 @@ impl<'tcx> Stack {
 self.unique_range = 0..0;
 }
 
-#[cfg(feature = "stack-cache-consistency-check")]
+#[cfg(feature = "expensive-consistency-checks")]
 self.verify_cache_consistency();
 interp_ok(())
 }

src/tools/miri/src/borrow_tracker/tree_borrows/diagnostics.rs

@@ -291,9 +291,10 @@ pub(super) struct TbError<'node> {
 pubconflicting_info:&'nodeNodeDebugInfo,
 // What kind of access caused this error (read, write, reborrow, deallocation)
 pubaccess_cause:AccessCause,
-/// Which tag the access that caused this error was made through, i.e.
+/// Which tag, if any, the access that caused this error was made through, i.e.
 /// which tag was used to read/write/deallocate.
-pubaccessed_info:&'nodeNodeDebugInfo,
+/// Not set on wildcard accesses.
+pubaccessed_info:Option<&'nodeNodeDebugInfo>,
 }
 
 implTbError<'_>{
@@ -302,10 +303,20 @@ impl TbError<'_> {
 useTransitionError::*;
 let cause = self.access_cause;
 let accessed = self.accessed_info;
+let accessed_str =
+self.accessed_info.map(|v| format!("{v}")).unwrap_or_else(|| "<wildcard>".into());
 let conflicting = self.conflicting_info;
-let accessed_is_conflicting = accessed.tag == conflicting.tag;
+// An access is considered conflicting if it happened through a
+// different tag than the one who caused UB.
+// When doing a wildcard access (where `accessed` is `None`) we
+// do not know which precise tag the accessed happened from,
+// however we can be certain that it did not come from the
+// conflicting tag.
+// This is because the wildcard data structure already removes
+// all tags through which an access would cause UB.
+let accessed_is_conflicting = accessed.map(|a| a.tag) == Some(conflicting.tag);
 let title = format!(
-"{cause} through {accessed} at {alloc_id:?}[{offset:#x}] is forbidden",
+"{cause} through {accessed_str} at {alloc_id:?}[{offset:#x}] is forbidden",
  alloc_id = self.alloc_id,
  offset = self.error_offset
 );
@@ -316,7 +327,7 @@ impl TbError<'_> {
 letmut details = Vec::new();
 if !accessed_is_conflicting {
  details.push(format!(
-"the accessed tag {accessed} is a child of the conflicting tag {conflicting}"
+"the accessed tag {accessed_str} is a child of the conflicting tag {conflicting}"
 ));
 }
 let access = cause.print_as_access(/* is_foreign */false);
@@ -330,7 +341,7 @@ impl TbError<'_> {
 let access = cause.print_as_access(/* is_foreign */true);
 let details = vec![
  format!(
-"the accessed tag {accessed} is foreign to the {conflicting_tag_name} tag {conflicting} (i.e., it is not a child)"
+"the accessed tag {accessed_str} is foreign to the {conflicting_tag_name} tag {conflicting} (i.e., it is not a child)"
 ),
  format!(
 "this {access} would cause the {conflicting_tag_name} tag {conflicting} (currently {before_disabled}) to become Disabled"
@@ -343,16 +354,18 @@ impl TbError<'_> {
 let conflicting_tag_name = "strongly protected";
 let details = vec![
  format!(
-"the allocation of the accessed tag {accessed} also contains the {conflicting_tag_name} tag {conflicting}"
+"the allocation of the accessed tag {accessed_str} also contains the {conflicting_tag_name} tag {conflicting}"
 ),
  format!("the {conflicting_tag_name} tag {conflicting} disallows deallocations"),
 ];
 (title, details, conflicting_tag_name)
 }
 };
 letmut history = HistoryData::default();
-if !accessed_is_conflicting {
- history.extend(self.accessed_info.history.forget(),"accessed",false);
+ifletSome(accessed_info) = self.accessed_info
+ && !accessed_is_conflicting
+{
+ history.extend(accessed_info.history.forget(),"accessed",false);
 }
  history.extend(
 self.conflicting_info.history.extract_relevant(self.error_offset,self.error_kind),
@@ -363,6 +376,20 @@ impl TbError<'_> {
 }
 }
 
+/// Cannot access this allocation with wildcard provenance, as there are no
+/// valid exposed references for this access kind.
+pubfnno_valid_exposed_references_error<'tcx>(
+alloc_id:AllocId,
+offset:u64,
+access_cause:AccessCause,
+) -> InterpErrorKind<'tcx>{
+let title =
+format!("{access_cause} through <wildcard> at {alloc_id:?}[{offset:#x}] is forbidden");
+let details = vec![format!("there are no exposed tags which may perform this access here")];
+let history = HistoryData::default();
+err_machine_stop!(TerminationInfo::TreeBorrowsUb{ title, details, history })
+}
+
 typeS = &'staticstr;
 /// Pretty-printing details
 ///
@@ -623,10 +650,10 @@ impl DisplayRepr {
 }else{
 // We take this node
 let rperm = tree
-.rperms
+.locations
 .iter_all()
-.map(move |(_offset,perms)| {
-let perm = perms.get(idx);
+.map(move |(_offset,loc)| {
+let perm = loc.perms.get(idx);
  perm.cloned()
 })
 .collect::<Vec<_>>();
@@ -788,7 +815,7 @@ impl<'tcx> Tree {
 show_unnamed:bool,
 ) -> InterpResult<'tcx>{
 letmut indenter = DisplayIndent::new();
-let ranges = self.rperms.iter_all().map(|(range,_perms)| range).collect::<Vec<_>>();
+let ranges = self.locations.iter_all().map(|(range,_loc)| range).collect::<Vec<_>>();
 ifletSome(repr) = DisplayRepr::from(self, show_unnamed){
  repr.print(
 &DEFAULT_FORMATTER,

src/tools/miri/src/borrow_tracker/tree_borrows/mod.rs

@@ -14,6 +14,7 @@ mod foreign_access_skipping;
 mod perms;
 mod tree;
 mod unimap;
+mod wildcard;
 
 #[cfg(test)]
 mod exhaustive;
@@ -54,16 +55,10 @@ impl<'tcx> Tree {
  interpret::Pointer::new(alloc_id, range.start),
  range.size.bytes(),
 );
-// TODO: for now we bail out on wildcard pointers. Eventually we should
-// handle them as much as we can.
-let tag = match prov {
-ProvenanceExtra::Concrete(tag) => tag,
-ProvenanceExtra::Wildcard => returninterp_ok(()),
-};
 let global = machine.borrow_tracker.as_ref().unwrap();
 let span = machine.current_user_relevant_span();
 self.perform_access(
-tag,
+prov,
 Some((range, access_kind, diagnostics::AccessCause::Explicit(access_kind))),
  global,
  alloc_id,
@@ -79,19 +74,9 @@ impl<'tcx> Tree {
 size:Size,
 machine:&MiriMachine<'tcx>,
 ) -> InterpResult<'tcx>{
-// TODO: for now we bail out on wildcard pointers. Eventually we should
-// handle them as much as we can.
-let tag = match prov {
-ProvenanceExtra::Concrete(tag) => tag,
-ProvenanceExtra::Wildcard => returninterp_ok(()),
-};
 let global = machine.borrow_tracker.as_ref().unwrap();
 let span = machine.current_user_relevant_span();
-self.dealloc(tag,alloc_range(Size::ZERO, size), global, alloc_id, span)
-}
-
-pubfnexpose_tag(&mutself,_tag:BorTag){
-// TODO
+self.dealloc(prov,alloc_range(Size::ZERO, size), global, alloc_id, span)
 }
 
 /// A tag just lost its protector.
@@ -109,7 +94,11 @@ impl<'tcx> Tree {
 ) -> InterpResult<'tcx>{
 let span = machine.current_user_relevant_span();
 // `None` makes it the magic on-protector-end operation
-self.perform_access(tag,None, global, alloc_id, span)
+self.perform_access(ProvenanceExtra::Concrete(tag),None, global, alloc_id, span)?;
+
+self.update_exposure_for_protector_release(tag);
+
+interp_ok(())
 }
 }
 
@@ -239,21 +228,22 @@ trait EvalContextPrivExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 assert_eq!(ptr_size,Size::ZERO);// we did the deref check above, size has to be 0 here
 // This pointer doesn't come with an AllocId, so there's no
 // memory to do retagging in.
+let new_prov = place.ptr().provenance;
 trace!(
-"reborrow of size 0: reference {:?} derived from {:?} (pointee {})",
- new_tag,
+"reborrow of size 0: reusing {:?} (pointee {})",
  place.ptr(),
  place.layout.ty,
 );
 log_creation(this,None)?;
 // Keep original provenance.
-returninterp_ok(place.ptr().provenance);
+returninterp_ok(new_prov);
 }
 };
+
 log_creation(this,Some((alloc_id, base_offset, parent_prov)))?;
 
 let orig_tag = match parent_prov {
-ProvenanceExtra::Wildcard => returninterp_ok(place.ptr().provenance),// TODO: handle wildcard pointers
+ProvenanceExtra::Wildcard => returninterp_ok(place.ptr().provenance),// TODO: handle retagging wildcard pointers
 ProvenanceExtra::Concrete(tag) => tag,
 };
 
@@ -356,7 +346,7 @@ trait EvalContextPrivExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 };
 
  tree_borrows.perform_access(
-orig_tag,
+parent_prov,
 Some((range_in_alloc,AccessKind::Read, diagnostics::AccessCause::Reborrow)),
  this.machine.borrow_tracker.as_ref().unwrap(),
  alloc_id,
@@ -589,7 +579,11 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 // uncovers a non-supported `extern static`.
 let alloc_extra = this.get_alloc_extra(alloc_id)?;
 trace!("Tree Borrows tag {tag:?} exposed in {alloc_id:?}");
- alloc_extra.borrow_tracker_tb().borrow_mut().expose_tag(tag);
+
+let global = this.machine.borrow_tracker.as_ref().unwrap();
+let protected_tags = &global.borrow().protected_tags;
+let protected = protected_tags.contains_key(&tag);
+ alloc_extra.borrow_tracker_tb().borrow_mut().expose_tag(tag, protected);
 }
 AllocKind::Function | AllocKind::VTable | AllocKind::TypeId | AllocKind::Dead => {
 // No tree borrows on these allocations.

src/tools/miri/src/borrow_tracker/tree_borrows/perms.rs

@@ -53,6 +53,7 @@ enum PermissionPriv {
 }
 useself::PermissionPriv::*;
 usesuper::foreign_access_skipping::IdempotentForeignAccess;
+usesuper::wildcard::WildcardAccessLevel;
 
 implPartialOrdforPermissionPriv{
 /// PermissionPriv is ordered by the reflexive transitive closure of
@@ -372,6 +373,23 @@ impl Permission {
 pubfnstrongest_idempotent_foreign_access(&self,prot:bool) -> IdempotentForeignAccess{
 self.inner.strongest_idempotent_foreign_access(prot)
 }
+
+/// Returns the strongest access allowed from a child to this node without
+/// causing UB (only considers possible transitions to this permission).
+pubfnstrongest_allowed_child_access(&self,protected:bool) -> WildcardAccessLevel{
+matchself.inner{
+// Everything except disabled can be accessed by read access.
+Disabled => WildcardAccessLevel::None,
+// Frozen references cannot be written to by a child.
+Frozen => WildcardAccessLevel::Read,
+// If the `conflicted` flag is set, then there was a foreign read
+// during the function call that is still ongoing (still `protected`),
+// this is UB (`noalias` violation).
+ReservedFrz{conflicted:true}if protected => WildcardAccessLevel::Read,
+// Everything else allows writes.
+ _ => WildcardAccessLevel::Write,
+}
+}
 }
 
 implPermTransition{
@@ -772,4 +790,32 @@ mod propagation_optimization_checks {
 );
 }
 }
+
+/// Checks that `strongest_allowed_child_access` correctly
+/// represents which transitions are possible.
+#[test]
+fnstrongest_allowed_child_access(){
+for(permission, protected)in <(Permission,bool)>::exhaustive(){
+let strongest_child_access = permission.strongest_allowed_child_access(protected);
+
+let is_read_valid = Permission::perform_access(
+AccessKind::Read,
+AccessRelatedness::LocalAccess,
+ permission,
+ protected,
+)
+.is_some();
+
+let is_write_valid = Permission::perform_access(
+AccessKind::Write,
+AccessRelatedness::LocalAccess,
+ permission,
+ protected,
+)
+.is_some();
+
+assert_eq!(is_read_valid, strongest_child_access >= WildcardAccessLevel::Read);
+assert_eq!(is_write_valid, strongest_child_access >= WildcardAccessLevel::Write);
+}
+}
 }

src/tools/miri/Cargo.toml

@@ -72,7 +72,7 @@ harness = false
 default = ["stack-cache", "native-lib"]
 genmc = ["dep:genmc-sys"]
 stack-cache = []
-stack-cache-consistency-check = ["stack-cache"]
+expensive-consistency-checks = ["stack-cache"]
 tracing = ["serde_json"]
 native-lib = ["dep:libffi", "dep:libloading", "dep:capstone", "dep:ipc-channel", "dep:nix", "dep:serde"]
 

src/tools/miri/src/bin/miri.rs

@@ -509,7 +509,6 @@ fn main() {
 Some(BorrowTrackerMethod::TreeBorrows(TreeBorrowsParams{
 precise_interior_mut:true,
 }));
- miri_config.provenance_mode = ProvenanceMode::Strict;
 }elseif arg == "-Zmiri-tree-borrows-no-precise-interior-mut"{
 match&mut miri_config.borrow_tracker{
 Some(BorrowTrackerMethod::TreeBorrows(params)) => {
@@ -703,17 +702,6 @@ fn main() {
  rustc_args.push(arg);
 }
 }
-// Tree Borrows implies strict provenance, and is not compatible with native calls.
-ifmatches!(miri_config.borrow_tracker,Some(BorrowTrackerMethod::TreeBorrows{ .. })){
-if miri_config.provenance_mode != ProvenanceMode::Strict{
-fatal_error!(
-"Tree Borrows does not support integer-to-pointer casts, and hence requires strict provenance"
-);
-}
-if !miri_config.native_lib.is_empty(){
-fatal_error!("Tree Borrows is not compatible with calling native functions");
-}
-}
 
 // Native calls and strict provenance are not compatible.
 if !miri_config.native_lib.is_empty() && miri_config.provenance_mode == ProvenanceMode::Strict{

src/tools/miri/src/borrow_tracker/mod.rs

@@ -352,6 +352,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 let borrow_tracker = this.machine.borrow_tracker.as_ref().unwrap();
 // The body of this loop needs `borrow_tracker` immutably
 // so we can't move this code inside the following `end_call`.
+
 for(alloc_id, tag)in&frame
 .extra
 .borrow_tracker
@@ -378,6 +379,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 }
 }
  borrow_tracker.borrow_mut().end_call(&frame.extra);
+
 interp_ok(())
 }
 }

src/tools/miri/src/borrow_tracker/stacked_borrows/stack.rs

@@ -153,7 +153,7 @@ impl<'tcx> Stack {
 /// Panics if any of the caching mechanisms have broken,
 /// - The StackCache indices don't refer to the parallel items,
 /// - There are no Unique items outside of first_unique..last_unique
-#[cfg(feature = "stack-cache-consistency-check")]
+#[cfg(feature = "expensive-consistency-checks")]
 fnverify_cache_consistency(&self){
 // Only a full cache needs to be valid. Also see the comments in find_granting_cache
 // and set_unknown_bottom.
@@ -197,7 +197,7 @@ impl<'tcx> Stack {
 tag:ProvenanceExtra,
 exposed_tags:&FxHashSet<BorTag>,
 ) -> Result<Option<usize>,()>{
-#[cfg(feature = "stack-cache-consistency-check")]
+#[cfg(feature = "expensive-consistency-checks")]
 self.verify_cache_consistency();
 
 letProvenanceExtra::Concrete(tag) = tag else{
@@ -334,7 +334,7 @@ impl<'tcx> Stack {
 // This primes the cache for the next access, which is almost always the just-added tag.
 self.cache.add(new_idx, new);
 
-#[cfg(feature = "stack-cache-consistency-check")]
+#[cfg(feature = "expensive-consistency-checks")]
 self.verify_cache_consistency();
 }
 
@@ -417,7 +417,7 @@ impl<'tcx> Stack {
 self.unique_range.end = self.unique_range.end.min(disable_start);
 }
 
-#[cfg(feature = "stack-cache-consistency-check")]
+#[cfg(feature = "expensive-consistency-checks")]
 self.verify_cache_consistency();
 
 interp_ok(())
@@ -472,7 +472,7 @@ impl<'tcx> Stack {
 self.unique_range = 0..0;
 }
 
-#[cfg(feature = "stack-cache-consistency-check")]
+#[cfg(feature = "expensive-consistency-checks")]
 self.verify_cache_consistency();
 interp_ok(())
 }

src/tools/miri/src/borrow_tracker/tree_borrows/diagnostics.rs

@@ -291,9 +291,10 @@ pub(super) struct TbError<'node> {
 pubconflicting_info:&'nodeNodeDebugInfo,
 // What kind of access caused this error (read, write, reborrow, deallocation)
 pubaccess_cause:AccessCause,
-/// Which tag the access that caused this error was made through, i.e.
+/// Which tag, if any, the access that caused this error was made through, i.e.
 /// which tag was used to read/write/deallocate.
-pubaccessed_info:&'nodeNodeDebugInfo,
+/// Not set on wildcard accesses.
+pubaccessed_info:Option<&'nodeNodeDebugInfo>,
 }
 
 implTbError<'_>{
@@ -302,10 +303,20 @@ impl TbError<'_> {
 useTransitionError::*;
 let cause = self.access_cause;
 let accessed = self.accessed_info;
+let accessed_str =
+self.accessed_info.map(|v| format!("{v}")).unwrap_or_else(|| "<wildcard>".into());
 let conflicting = self.conflicting_info;
-let accessed_is_conflicting = accessed.tag == conflicting.tag;
+// An access is considered conflicting if it happened through a
+// different tag than the one who caused UB.
+// When doing a wildcard access (where `accessed` is `None`) we
+// do not know which precise tag the accessed happened from,
+// however we can be certain that it did not come from the
+// conflicting tag.
+// This is because the wildcard data structure already removes
+// all tags through which an access would cause UB.
+let accessed_is_conflicting = accessed.map(|a| a.tag) == Some(conflicting.tag);
 let title = format!(
-"{cause} through {accessed} at {alloc_id:?}[{offset:#x}] is forbidden",
+"{cause} through {accessed_str} at {alloc_id:?}[{offset:#x}] is forbidden",
  alloc_id = self.alloc_id,
  offset = self.error_offset
 );
@@ -316,7 +327,7 @@ impl TbError<'_> {
 letmut details = Vec::new();
 if !accessed_is_conflicting {
  details.push(format!(
-"the accessed tag {accessed} is a child of the conflicting tag {conflicting}"
+"the accessed tag {accessed_str} is a child of the conflicting tag {conflicting}"
 ));
 }
 let access = cause.print_as_access(/* is_foreign */false);
@@ -330,7 +341,7 @@ impl TbError<'_> {
 let access = cause.print_as_access(/* is_foreign */true);
 let details = vec![
  format!(
-"the accessed tag {accessed} is foreign to the {conflicting_tag_name} tag {conflicting} (i.e., it is not a child)"
+"the accessed tag {accessed_str} is foreign to the {conflicting_tag_name} tag {conflicting} (i.e., it is not a child)"
 ),
  format!(
 "this {access} would cause the {conflicting_tag_name} tag {conflicting} (currently {before_disabled}) to become Disabled"
@@ -343,16 +354,18 @@ impl TbError<'_> {
 let conflicting_tag_name = "strongly protected";
 let details = vec![
  format!(
-"the allocation of the accessed tag {accessed} also contains the {conflicting_tag_name} tag {conflicting}"
+"the allocation of the accessed tag {accessed_str} also contains the {conflicting_tag_name} tag {conflicting}"
 ),
  format!("the {conflicting_tag_name} tag {conflicting} disallows deallocations"),
 ];
 (title, details, conflicting_tag_name)
 }
 };
 letmut history = HistoryData::default();
-if !accessed_is_conflicting {
- history.extend(self.accessed_info.history.forget(),"accessed",false);
+ifletSome(accessed_info) = self.accessed_info
+ && !accessed_is_conflicting
+{
+ history.extend(accessed_info.history.forget(),"accessed",false);
 }
  history.extend(
 self.conflicting_info.history.extract_relevant(self.error_offset,self.error_kind),
@@ -363,6 +376,20 @@ impl TbError<'_> {
 }
 }
 
+/// Cannot access this allocation with wildcard provenance, as there are no
+/// valid exposed references for this access kind.
+pubfnno_valid_exposed_references_error<'tcx>(
+alloc_id:AllocId,
+offset:u64,
+access_cause:AccessCause,
+) -> InterpErrorKind<'tcx>{
+let title =
+format!("{access_cause} through <wildcard> at {alloc_id:?}[{offset:#x}] is forbidden");
+let details = vec![format!("there are no exposed tags which may perform this access here")];
+let history = HistoryData::default();
+err_machine_stop!(TerminationInfo::TreeBorrowsUb{ title, details, history })
+}
+
 typeS = &'staticstr;
 /// Pretty-printing details
 ///
@@ -623,10 +650,10 @@ impl DisplayRepr {
 }else{
 // We take this node
 let rperm = tree
-.rperms
+.locations
 .iter_all()
-.map(move |(_offset,perms)| {
-let perm = perms.get(idx);
+.map(move |(_offset,loc)| {
+let perm = loc.perms.get(idx);
  perm.cloned()
 })
 .collect::<Vec<_>>();
@@ -788,7 +815,7 @@ impl<'tcx> Tree {
 show_unnamed:bool,
 ) -> InterpResult<'tcx>{
 letmut indenter = DisplayIndent::new();
-let ranges = self.rperms.iter_all().map(|(range,_perms)| range).collect::<Vec<_>>();
+let ranges = self.locations.iter_all().map(|(range,_loc)| range).collect::<Vec<_>>();
 ifletSome(repr) = DisplayRepr::from(self, show_unnamed){
  repr.print(
 &DEFAULT_FORMATTER,

src/tools/miri/src/borrow_tracker/tree_borrows/mod.rs

@@ -14,6 +14,7 @@ mod foreign_access_skipping;
 mod perms;
 mod tree;
 mod unimap;
+mod wildcard;
 
 #[cfg(test)]
 mod exhaustive;
@@ -54,16 +55,10 @@ impl<'tcx> Tree {
  interpret::Pointer::new(alloc_id, range.start),
  range.size.bytes(),
 );
-// TODO: for now we bail out on wildcard pointers. Eventually we should
-// handle them as much as we can.
-let tag = match prov {
-ProvenanceExtra::Concrete(tag) => tag,
-ProvenanceExtra::Wildcard => returninterp_ok(()),
-};
 let global = machine.borrow_tracker.as_ref().unwrap();
 let span = machine.current_user_relevant_span();
 self.perform_access(
-tag,
+prov,
 Some((range, access_kind, diagnostics::AccessCause::Explicit(access_kind))),
  global,
  alloc_id,
@@ -79,19 +74,9 @@ impl<'tcx> Tree {
 size:Size,
 machine:&MiriMachine<'tcx>,
 ) -> InterpResult<'tcx>{
-// TODO: for now we bail out on wildcard pointers. Eventually we should
-// handle them as much as we can.
-let tag = match prov {
-ProvenanceExtra::Concrete(tag) => tag,
-ProvenanceExtra::Wildcard => returninterp_ok(()),
-};
 let global = machine.borrow_tracker.as_ref().unwrap();
 let span = machine.current_user_relevant_span();
-self.dealloc(tag,alloc_range(Size::ZERO, size), global, alloc_id, span)
-}
-
-pubfnexpose_tag(&mutself,_tag:BorTag){
-// TODO
+self.dealloc(prov,alloc_range(Size::ZERO, size), global, alloc_id, span)
 }
 
 /// A tag just lost its protector.
@@ -109,7 +94,11 @@ impl<'tcx> Tree {
 ) -> InterpResult<'tcx>{
 let span = machine.current_user_relevant_span();
 // `None` makes it the magic on-protector-end operation
-self.perform_access(tag,None, global, alloc_id, span)
+self.perform_access(ProvenanceExtra::Concrete(tag),None, global, alloc_id, span)?;
+
+self.update_exposure_for_protector_release(tag);
+
+interp_ok(())
 }
 }
 
@@ -239,21 +228,22 @@ trait EvalContextPrivExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 assert_eq!(ptr_size,Size::ZERO);// we did the deref check above, size has to be 0 here
 // This pointer doesn't come with an AllocId, so there's no
 // memory to do retagging in.
+let new_prov = place.ptr().provenance;
 trace!(
-"reborrow of size 0: reference {:?} derived from {:?} (pointee {})",
- new_tag,
+"reborrow of size 0: reusing {:?} (pointee {})",
  place.ptr(),
  place.layout.ty,
 );
 log_creation(this,None)?;
 // Keep original provenance.
-returninterp_ok(place.ptr().provenance);
+returninterp_ok(new_prov);
 }
 };
+
 log_creation(this,Some((alloc_id, base_offset, parent_prov)))?;
 
 let orig_tag = match parent_prov {
-ProvenanceExtra::Wildcard => returninterp_ok(place.ptr().provenance),// TODO: handle wildcard pointers
+ProvenanceExtra::Wildcard => returninterp_ok(place.ptr().provenance),// TODO: handle retagging wildcard pointers
 ProvenanceExtra::Concrete(tag) => tag,
 };
 
@@ -356,7 +346,7 @@ trait EvalContextPrivExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 };
 
  tree_borrows.perform_access(
-orig_tag,
+parent_prov,
 Some((range_in_alloc,AccessKind::Read, diagnostics::AccessCause::Reborrow)),
  this.machine.borrow_tracker.as_ref().unwrap(),
  alloc_id,
@@ -589,7 +579,11 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 // uncovers a non-supported `extern static`.
 let alloc_extra = this.get_alloc_extra(alloc_id)?;
 trace!("Tree Borrows tag {tag:?} exposed in {alloc_id:?}");
- alloc_extra.borrow_tracker_tb().borrow_mut().expose_tag(tag);
+
+let global = this.machine.borrow_tracker.as_ref().unwrap();
+let protected_tags = &global.borrow().protected_tags;
+let protected = protected_tags.contains_key(&tag);
+ alloc_extra.borrow_tracker_tb().borrow_mut().expose_tag(tag, protected);
 }
 AllocKind::Function | AllocKind::VTable | AllocKind::TypeId | AllocKind::Dead => {
 // No tree borrows on these allocations.

src/tools/miri/src/borrow_tracker/tree_borrows/perms.rs

@@ -53,6 +53,7 @@ enum PermissionPriv {
 }
 useself::PermissionPriv::*;
 usesuper::foreign_access_skipping::IdempotentForeignAccess;
+usesuper::wildcard::WildcardAccessLevel;
 
 implPartialOrdforPermissionPriv{
 /// PermissionPriv is ordered by the reflexive transitive closure of
@@ -372,6 +373,23 @@ impl Permission {
 pubfnstrongest_idempotent_foreign_access(&self,prot:bool) -> IdempotentForeignAccess{
 self.inner.strongest_idempotent_foreign_access(prot)
 }
+
+/// Returns the strongest access allowed from a child to this node without
+/// causing UB (only considers possible transitions to this permission).
+pubfnstrongest_allowed_child_access(&self,protected:bool) -> WildcardAccessLevel{
+matchself.inner{
+// Everything except disabled can be accessed by read access.
+Disabled => WildcardAccessLevel::None,
+// Frozen references cannot be written to by a child.
+Frozen => WildcardAccessLevel::Read,
+// If the `conflicted` flag is set, then there was a foreign read
+// during the function call that is still ongoing (still `protected`),
+// this is UB (`noalias` violation).
+ReservedFrz{conflicted:true}if protected => WildcardAccessLevel::Read,
+// Everything else allows writes.
+ _ => WildcardAccessLevel::Write,
+}
+}
 }
 
 implPermTransition{
@@ -772,4 +790,32 @@ mod propagation_optimization_checks {
 );
 }
 }
+
+/// Checks that `strongest_allowed_child_access` correctly
+/// represents which transitions are possible.
+#[test]
+fnstrongest_allowed_child_access(){
+for(permission, protected)in <(Permission,bool)>::exhaustive(){
+let strongest_child_access = permission.strongest_allowed_child_access(protected);
+
+let is_read_valid = Permission::perform_access(
+AccessKind::Read,
+AccessRelatedness::LocalAccess,
+ permission,
+ protected,
+)
+.is_some();
+
+let is_write_valid = Permission::perform_access(
+AccessKind::Write,
+AccessRelatedness::LocalAccess,
+ permission,
+ protected,
+)
+.is_some();
+
+assert_eq!(is_read_valid, strongest_child_access >= WildcardAccessLevel::Read);
+assert_eq!(is_write_valid, strongest_child_access >= WildcardAccessLevel::Write);
+}
+}
 }

src/tools/miri/Cargo.toml

@@ -72,7 +72,7 @@ harness = false
 default = ["stack-cache", "native-lib"]
 genmc = ["dep:genmc-sys"]
 stack-cache = []
-stack-cache-consistency-check = ["stack-cache"]
+expensive-consistency-checks = ["stack-cache"]
 tracing = ["serde_json"]
 native-lib = ["dep:libffi", "dep:libloading", "dep:capstone", "dep:ipc-channel", "dep:nix", "dep:serde"]
 

src/tools/miri/src/bin/miri.rs

@@ -509,7 +509,6 @@ fn main() {
 Some(BorrowTrackerMethod::TreeBorrows(TreeBorrowsParams{
 precise_interior_mut:true,
 }));
- miri_config.provenance_mode = ProvenanceMode::Strict;
 }elseif arg == "-Zmiri-tree-borrows-no-precise-interior-mut"{
 match&mut miri_config.borrow_tracker{
 Some(BorrowTrackerMethod::TreeBorrows(params)) => {
@@ -703,17 +702,6 @@ fn main() {
  rustc_args.push(arg);
 }
 }
-// Tree Borrows implies strict provenance, and is not compatible with native calls.
-ifmatches!(miri_config.borrow_tracker,Some(BorrowTrackerMethod::TreeBorrows{ .. })){
-if miri_config.provenance_mode != ProvenanceMode::Strict{
-fatal_error!(
-"Tree Borrows does not support integer-to-pointer casts, and hence requires strict provenance"
-);
-}
-if !miri_config.native_lib.is_empty(){
-fatal_error!("Tree Borrows is not compatible with calling native functions");
-}
-}
 
 // Native calls and strict provenance are not compatible.
 if !miri_config.native_lib.is_empty() && miri_config.provenance_mode == ProvenanceMode::Strict{

src/tools/miri/src/borrow_tracker/mod.rs

@@ -352,6 +352,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 let borrow_tracker = this.machine.borrow_tracker.as_ref().unwrap();
 // The body of this loop needs `borrow_tracker` immutably
 // so we can't move this code inside the following `end_call`.
+
 for(alloc_id, tag)in&frame
 .extra
 .borrow_tracker
@@ -378,6 +379,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 }
 }
  borrow_tracker.borrow_mut().end_call(&frame.extra);
+
 interp_ok(())
 }
 }

src/tools/miri/src/borrow_tracker/stacked_borrows/stack.rs

@@ -153,7 +153,7 @@ impl<'tcx> Stack {
 /// Panics if any of the caching mechanisms have broken,
 /// - The StackCache indices don't refer to the parallel items,
 /// - There are no Unique items outside of first_unique..last_unique
-#[cfg(feature = "stack-cache-consistency-check")]
+#[cfg(feature = "expensive-consistency-checks")]
 fnverify_cache_consistency(&self){
 // Only a full cache needs to be valid. Also see the comments in find_granting_cache
 // and set_unknown_bottom.
@@ -197,7 +197,7 @@ impl<'tcx> Stack {
 tag:ProvenanceExtra,
 exposed_tags:&FxHashSet<BorTag>,
 ) -> Result<Option<usize>,()>{
-#[cfg(feature = "stack-cache-consistency-check")]
+#[cfg(feature = "expensive-consistency-checks")]
 self.verify_cache_consistency();
 
 letProvenanceExtra::Concrete(tag) = tag else{
@@ -334,7 +334,7 @@ impl<'tcx> Stack {
 // This primes the cache for the next access, which is almost always the just-added tag.
 self.cache.add(new_idx, new);
 
-#[cfg(feature = "stack-cache-consistency-check")]
+#[cfg(feature = "expensive-consistency-checks")]
 self.verify_cache_consistency();
 }
 
@@ -417,7 +417,7 @@ impl<'tcx> Stack {
 self.unique_range.end = self.unique_range.end.min(disable_start);
 }
 
-#[cfg(feature = "stack-cache-consistency-check")]
+#[cfg(feature = "expensive-consistency-checks")]
 self.verify_cache_consistency();
 
 interp_ok(())
@@ -472,7 +472,7 @@ impl<'tcx> Stack {
 self.unique_range = 0..0;
 }
 
-#[cfg(feature = "stack-cache-consistency-check")]
+#[cfg(feature = "expensive-consistency-checks")]
 self.verify_cache_consistency();
 interp_ok(())
 }

src/tools/miri/src/borrow_tracker/tree_borrows/diagnostics.rs

@@ -291,9 +291,10 @@ pub(super) struct TbError<'node> {
 pubconflicting_info:&'nodeNodeDebugInfo,
 // What kind of access caused this error (read, write, reborrow, deallocation)
 pubaccess_cause:AccessCause,
-/// Which tag the access that caused this error was made through, i.e.
+/// Which tag, if any, the access that caused this error was made through, i.e.
 /// which tag was used to read/write/deallocate.
-pubaccessed_info:&'nodeNodeDebugInfo,
+/// Not set on wildcard accesses.
+pubaccessed_info:Option<&'nodeNodeDebugInfo>,
 }
 
 implTbError<'_>{
@@ -302,10 +303,20 @@ impl TbError<'_> {
 useTransitionError::*;
 let cause = self.access_cause;
 let accessed = self.accessed_info;
+let accessed_str =
+self.accessed_info.map(|v| format!("{v}")).unwrap_or_else(|| "<wildcard>".into());
 let conflicting = self.conflicting_info;
-let accessed_is_conflicting = accessed.tag == conflicting.tag;
+// An access is considered conflicting if it happened through a
+// different tag than the one who caused UB.
+// When doing a wildcard access (where `accessed` is `None`) we
+// do not know which precise tag the accessed happened from,
+// however we can be certain that it did not come from the
+// conflicting tag.
+// This is because the wildcard data structure already removes
+// all tags through which an access would cause UB.
+let accessed_is_conflicting = accessed.map(|a| a.tag) == Some(conflicting.tag);
 let title = format!(
-"{cause} through {accessed} at {alloc_id:?}[{offset:#x}] is forbidden",
+"{cause} through {accessed_str} at {alloc_id:?}[{offset:#x}] is forbidden",
  alloc_id = self.alloc_id,
  offset = self.error_offset
 );
@@ -316,7 +327,7 @@ impl TbError<'_> {
 letmut details = Vec::new();
 if !accessed_is_conflicting {
  details.push(format!(
-"the accessed tag {accessed} is a child of the conflicting tag {conflicting}"
+"the accessed tag {accessed_str} is a child of the conflicting tag {conflicting}"
 ));
 }
 let access = cause.print_as_access(/* is_foreign */false);
@@ -330,7 +341,7 @@ impl TbError<'_> {
 let access = cause.print_as_access(/* is_foreign */true);
 let details = vec![
  format!(
-"the accessed tag {accessed} is foreign to the {conflicting_tag_name} tag {conflicting} (i.e., it is not a child)"
+"the accessed tag {accessed_str} is foreign to the {conflicting_tag_name} tag {conflicting} (i.e., it is not a child)"
 ),
  format!(
 "this {access} would cause the {conflicting_tag_name} tag {conflicting} (currently {before_disabled}) to become Disabled"
@@ -343,16 +354,18 @@ impl TbError<'_> {
 let conflicting_tag_name = "strongly protected";
 let details = vec![
  format!(
-"the allocation of the accessed tag {accessed} also contains the {conflicting_tag_name} tag {conflicting}"
+"the allocation of the accessed tag {accessed_str} also contains the {conflicting_tag_name} tag {conflicting}"
 ),
  format!("the {conflicting_tag_name} tag {conflicting} disallows deallocations"),
 ];
 (title, details, conflicting_tag_name)
 }
 };
 letmut history = HistoryData::default();
-if !accessed_is_conflicting {
- history.extend(self.accessed_info.history.forget(),"accessed",false);
+ifletSome(accessed_info) = self.accessed_info
+ && !accessed_is_conflicting
+{
+ history.extend(accessed_info.history.forget(),"accessed",false);
 }
  history.extend(
 self.conflicting_info.history.extract_relevant(self.error_offset,self.error_kind),
@@ -363,6 +376,20 @@ impl TbError<'_> {
 }
 }
 
+/// Cannot access this allocation with wildcard provenance, as there are no
+/// valid exposed references for this access kind.
+pubfnno_valid_exposed_references_error<'tcx>(
+alloc_id:AllocId,
+offset:u64,
+access_cause:AccessCause,
+) -> InterpErrorKind<'tcx>{
+let title =
+format!("{access_cause} through <wildcard> at {alloc_id:?}[{offset:#x}] is forbidden");
+let details = vec![format!("there are no exposed tags which may perform this access here")];
+let history = HistoryData::default();
+err_machine_stop!(TerminationInfo::TreeBorrowsUb{ title, details, history })
+}
+
 typeS = &'staticstr;
 /// Pretty-printing details
 ///
@@ -623,10 +650,10 @@ impl DisplayRepr {
 }else{
 // We take this node
 let rperm = tree
-.rperms
+.locations
 .iter_all()
-.map(move |(_offset,perms)| {
-let perm = perms.get(idx);
+.map(move |(_offset,loc)| {
+let perm = loc.perms.get(idx);
  perm.cloned()
 })
 .collect::<Vec<_>>();
@@ -788,7 +815,7 @@ impl<'tcx> Tree {
 show_unnamed:bool,
 ) -> InterpResult<'tcx>{
 letmut indenter = DisplayIndent::new();
-let ranges = self.rperms.iter_all().map(|(range,_perms)| range).collect::<Vec<_>>();
+let ranges = self.locations.iter_all().map(|(range,_loc)| range).collect::<Vec<_>>();
 ifletSome(repr) = DisplayRepr::from(self, show_unnamed){
  repr.print(
 &DEFAULT_FORMATTER,

src/tools/miri/src/borrow_tracker/tree_borrows/mod.rs

@@ -14,6 +14,7 @@ mod foreign_access_skipping;
 mod perms;
 mod tree;
 mod unimap;
+mod wildcard;
 
 #[cfg(test)]
 mod exhaustive;
@@ -54,16 +55,10 @@ impl<'tcx> Tree {
  interpret::Pointer::new(alloc_id, range.start),
  range.size.bytes(),
 );
-// TODO: for now we bail out on wildcard pointers. Eventually we should
-// handle them as much as we can.
-let tag = match prov {
-ProvenanceExtra::Concrete(tag) => tag,
-ProvenanceExtra::Wildcard => returninterp_ok(()),
-};
 let global = machine.borrow_tracker.as_ref().unwrap();
 let span = machine.current_user_relevant_span();
 self.perform_access(
-tag,
+prov,
 Some((range, access_kind, diagnostics::AccessCause::Explicit(access_kind))),
  global,
  alloc_id,
@@ -79,19 +74,9 @@ impl<'tcx> Tree {
 size:Size,
 machine:&MiriMachine<'tcx>,
 ) -> InterpResult<'tcx>{
-// TODO: for now we bail out on wildcard pointers. Eventually we should
-// handle them as much as we can.
-let tag = match prov {
-ProvenanceExtra::Concrete(tag) => tag,
-ProvenanceExtra::Wildcard => returninterp_ok(()),
-};
 let global = machine.borrow_tracker.as_ref().unwrap();
 let span = machine.current_user_relevant_span();
-self.dealloc(tag,alloc_range(Size::ZERO, size), global, alloc_id, span)
-}
-
-pubfnexpose_tag(&mutself,_tag:BorTag){
-// TODO
+self.dealloc(prov,alloc_range(Size::ZERO, size), global, alloc_id, span)
 }
 
 /// A tag just lost its protector.
@@ -109,7 +94,11 @@ impl<'tcx> Tree {
 ) -> InterpResult<'tcx>{
 let span = machine.current_user_relevant_span();
 // `None` makes it the magic on-protector-end operation
-self.perform_access(tag,None, global, alloc_id, span)
+self.perform_access(ProvenanceExtra::Concrete(tag),None, global, alloc_id, span)?;
+
+self.update_exposure_for_protector_release(tag);
+
+interp_ok(())
 }
 }
 
@@ -239,21 +228,22 @@ trait EvalContextPrivExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 assert_eq!(ptr_size,Size::ZERO);// we did the deref check above, size has to be 0 here
 // This pointer doesn't come with an AllocId, so there's no
 // memory to do retagging in.
+let new_prov = place.ptr().provenance;
 trace!(
-"reborrow of size 0: reference {:?} derived from {:?} (pointee {})",
- new_tag,
+"reborrow of size 0: reusing {:?} (pointee {})",
  place.ptr(),
  place.layout.ty,
 );
 log_creation(this,None)?;
 // Keep original provenance.
-returninterp_ok(place.ptr().provenance);
+returninterp_ok(new_prov);
 }
 };
+
 log_creation(this,Some((alloc_id, base_offset, parent_prov)))?;
 
 let orig_tag = match parent_prov {
-ProvenanceExtra::Wildcard => returninterp_ok(place.ptr().provenance),// TODO: handle wildcard pointers
+ProvenanceExtra::Wildcard => returninterp_ok(place.ptr().provenance),// TODO: handle retagging wildcard pointers
 ProvenanceExtra::Concrete(tag) => tag,
 };
 
@@ -356,7 +346,7 @@ trait EvalContextPrivExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 };
 
  tree_borrows.perform_access(
-orig_tag,
+parent_prov,
 Some((range_in_alloc,AccessKind::Read, diagnostics::AccessCause::Reborrow)),
  this.machine.borrow_tracker.as_ref().unwrap(),
  alloc_id,
@@ -589,7 +579,11 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 // uncovers a non-supported `extern static`.
 let alloc_extra = this.get_alloc_extra(alloc_id)?;
 trace!("Tree Borrows tag {tag:?} exposed in {alloc_id:?}");
- alloc_extra.borrow_tracker_tb().borrow_mut().expose_tag(tag);
+
+let global = this.machine.borrow_tracker.as_ref().unwrap();
+let protected_tags = &global.borrow().protected_tags;
+let protected = protected_tags.contains_key(&tag);
+ alloc_extra.borrow_tracker_tb().borrow_mut().expose_tag(tag, protected);
 }
 AllocKind::Function | AllocKind::VTable | AllocKind::TypeId | AllocKind::Dead => {
 // No tree borrows on these allocations.

src/tools/miri/src/borrow_tracker/tree_borrows/perms.rs

@@ -53,6 +53,7 @@ enum PermissionPriv {
 }
 useself::PermissionPriv::*;
 usesuper::foreign_access_skipping::IdempotentForeignAccess;
+usesuper::wildcard::WildcardAccessLevel;
 
 implPartialOrdforPermissionPriv{
 /// PermissionPriv is ordered by the reflexive transitive closure of
@@ -372,6 +373,23 @@ impl Permission {
 pubfnstrongest_idempotent_foreign_access(&self,prot:bool) -> IdempotentForeignAccess{
 self.inner.strongest_idempotent_foreign_access(prot)
 }
+
+/// Returns the strongest access allowed from a child to this node without
+/// causing UB (only considers possible transitions to this permission).
+pubfnstrongest_allowed_child_access(&self,protected:bool) -> WildcardAccessLevel{
+matchself.inner{
+// Everything except disabled can be accessed by read access.
+Disabled => WildcardAccessLevel::None,
+// Frozen references cannot be written to by a child.
+Frozen => WildcardAccessLevel::Read,
+// If the `conflicted` flag is set, then there was a foreign read
+// during the function call that is still ongoing (still `protected`),
+// this is UB (`noalias` violation).
+ReservedFrz{conflicted:true}if protected => WildcardAccessLevel::Read,
+// Everything else allows writes.
+ _ => WildcardAccessLevel::Write,
+}
+}
 }
 
 implPermTransition{
@@ -772,4 +790,32 @@ mod propagation_optimization_checks {
 );
 }
 }
+
+/// Checks that `strongest_allowed_child_access` correctly
+/// represents which transitions are possible.
+#[test]
+fnstrongest_allowed_child_access(){
+for(permission, protected)in <(Permission,bool)>::exhaustive(){
+let strongest_child_access = permission.strongest_allowed_child_access(protected);
+
+let is_read_valid = Permission::perform_access(
+AccessKind::Read,
+AccessRelatedness::LocalAccess,
+ permission,
+ protected,
+)
+.is_some();
+
+let is_write_valid = Permission::perform_access(
+AccessKind::Write,
+AccessRelatedness::LocalAccess,
+ permission,
+ protected,
+)
+.is_some();
+
+assert_eq!(is_read_valid, strongest_child_access >= WildcardAccessLevel::Read);
+assert_eq!(is_write_valid, strongest_child_access >= WildcardAccessLevel::Write);
+}
+}
 }

src/tools/miri/Cargo.toml

@@ -72,7 +72,7 @@ harness = false
 default = ["stack-cache", "native-lib"]
 genmc = ["dep:genmc-sys"]
 stack-cache = []
-stack-cache-consistency-check = ["stack-cache"]
+expensive-consistency-checks = ["stack-cache"]
 tracing = ["serde_json"]
 native-lib = ["dep:libffi", "dep:libloading", "dep:capstone", "dep:ipc-channel", "dep:nix", "dep:serde"]
 

src/tools/miri/src/bin/miri.rs

@@ -509,7 +509,6 @@ fn main() {
 Some(BorrowTrackerMethod::TreeBorrows(TreeBorrowsParams{
 precise_interior_mut:true,
 }));
- miri_config.provenance_mode = ProvenanceMode::Strict;
 }elseif arg == "-Zmiri-tree-borrows-no-precise-interior-mut"{
 match&mut miri_config.borrow_tracker{
 Some(BorrowTrackerMethod::TreeBorrows(params)) => {
@@ -703,17 +702,6 @@ fn main() {
  rustc_args.push(arg);
 }
 }
-// Tree Borrows implies strict provenance, and is not compatible with native calls.
-ifmatches!(miri_config.borrow_tracker,Some(BorrowTrackerMethod::TreeBorrows{ .. })){
-if miri_config.provenance_mode != ProvenanceMode::Strict{
-fatal_error!(
-"Tree Borrows does not support integer-to-pointer casts, and hence requires strict provenance"
-);
-}
-if !miri_config.native_lib.is_empty(){
-fatal_error!("Tree Borrows is not compatible with calling native functions");
-}
-}
 
 // Native calls and strict provenance are not compatible.
 if !miri_config.native_lib.is_empty() && miri_config.provenance_mode == ProvenanceMode::Strict{

src/tools/miri/src/borrow_tracker/mod.rs

@@ -352,6 +352,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 let borrow_tracker = this.machine.borrow_tracker.as_ref().unwrap();
 // The body of this loop needs `borrow_tracker` immutably
 // so we can't move this code inside the following `end_call`.
+
 for(alloc_id, tag)in&frame
 .extra
 .borrow_tracker
@@ -378,6 +379,7 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 }
 }
  borrow_tracker.borrow_mut().end_call(&frame.extra);
+
 interp_ok(())
 }
 }

src/tools/miri/src/borrow_tracker/stacked_borrows/stack.rs

@@ -153,7 +153,7 @@ impl<'tcx> Stack {
 /// Panics if any of the caching mechanisms have broken,
 /// - The StackCache indices don't refer to the parallel items,
 /// - There are no Unique items outside of first_unique..last_unique
-#[cfg(feature = "stack-cache-consistency-check")]
+#[cfg(feature = "expensive-consistency-checks")]
 fnverify_cache_consistency(&self){
 // Only a full cache needs to be valid. Also see the comments in find_granting_cache
 // and set_unknown_bottom.
@@ -197,7 +197,7 @@ impl<'tcx> Stack {
 tag:ProvenanceExtra,
 exposed_tags:&FxHashSet<BorTag>,
 ) -> Result<Option<usize>,()>{
-#[cfg(feature = "stack-cache-consistency-check")]
+#[cfg(feature = "expensive-consistency-checks")]
 self.verify_cache_consistency();
 
 letProvenanceExtra::Concrete(tag) = tag else{
@@ -334,7 +334,7 @@ impl<'tcx> Stack {
 // This primes the cache for the next access, which is almost always the just-added tag.
 self.cache.add(new_idx, new);
 
-#[cfg(feature = "stack-cache-consistency-check")]
+#[cfg(feature = "expensive-consistency-checks")]
 self.verify_cache_consistency();
 }
 
@@ -417,7 +417,7 @@ impl<'tcx> Stack {
 self.unique_range.end = self.unique_range.end.min(disable_start);
 }
 
-#[cfg(feature = "stack-cache-consistency-check")]
+#[cfg(feature = "expensive-consistency-checks")]
 self.verify_cache_consistency();
 
 interp_ok(())
@@ -472,7 +472,7 @@ impl<'tcx> Stack {
 self.unique_range = 0..0;
 }
 
-#[cfg(feature = "stack-cache-consistency-check")]
+#[cfg(feature = "expensive-consistency-checks")]
 self.verify_cache_consistency();
 interp_ok(())
 }

src/tools/miri/src/borrow_tracker/tree_borrows/diagnostics.rs

@@ -291,9 +291,10 @@ pub(super) struct TbError<'node> {
 pubconflicting_info:&'nodeNodeDebugInfo,
 // What kind of access caused this error (read, write, reborrow, deallocation)
 pubaccess_cause:AccessCause,
-/// Which tag the access that caused this error was made through, i.e.
+/// Which tag, if any, the access that caused this error was made through, i.e.
 /// which tag was used to read/write/deallocate.
-pubaccessed_info:&'nodeNodeDebugInfo,
+/// Not set on wildcard accesses.
+pubaccessed_info:Option<&'nodeNodeDebugInfo>,
 }
 
 implTbError<'_>{
@@ -302,10 +303,20 @@ impl TbError<'_> {
 useTransitionError::*;
 let cause = self.access_cause;
 let accessed = self.accessed_info;
+let accessed_str =
+self.accessed_info.map(|v| format!("{v}")).unwrap_or_else(|| "<wildcard>".into());
 let conflicting = self.conflicting_info;
-let accessed_is_conflicting = accessed.tag == conflicting.tag;
+// An access is considered conflicting if it happened through a
+// different tag than the one who caused UB.
+// When doing a wildcard access (where `accessed` is `None`) we
+// do not know which precise tag the accessed happened from,
+// however we can be certain that it did not come from the
+// conflicting tag.
+// This is because the wildcard data structure already removes
+// all tags through which an access would cause UB.
+let accessed_is_conflicting = accessed.map(|a| a.tag) == Some(conflicting.tag);
 let title = format!(
-"{cause} through {accessed} at {alloc_id:?}[{offset:#x}] is forbidden",
+"{cause} through {accessed_str} at {alloc_id:?}[{offset:#x}] is forbidden",
  alloc_id = self.alloc_id,
  offset = self.error_offset
 );
@@ -316,7 +327,7 @@ impl TbError<'_> {
 letmut details = Vec::new();
 if !accessed_is_conflicting {
  details.push(format!(
-"the accessed tag {accessed} is a child of the conflicting tag {conflicting}"
+"the accessed tag {accessed_str} is a child of the conflicting tag {conflicting}"
 ));
 }
 let access = cause.print_as_access(/* is_foreign */false);
@@ -330,7 +341,7 @@ impl TbError<'_> {
 let access = cause.print_as_access(/* is_foreign */true);
 let details = vec![
  format!(
-"the accessed tag {accessed} is foreign to the {conflicting_tag_name} tag {conflicting} (i.e., it is not a child)"
+"the accessed tag {accessed_str} is foreign to the {conflicting_tag_name} tag {conflicting} (i.e., it is not a child)"
 ),
  format!(
 "this {access} would cause the {conflicting_tag_name} tag {conflicting} (currently {before_disabled}) to become Disabled"
@@ -343,16 +354,18 @@ impl TbError<'_> {
 let conflicting_tag_name = "strongly protected";
 let details = vec![
  format!(
-"the allocation of the accessed tag {accessed} also contains the {conflicting_tag_name} tag {conflicting}"
+"the allocation of the accessed tag {accessed_str} also contains the {conflicting_tag_name} tag {conflicting}"
 ),
  format!("the {conflicting_tag_name} tag {conflicting} disallows deallocations"),
 ];
 (title, details, conflicting_tag_name)
 }
 };
 letmut history = HistoryData::default();
-if !accessed_is_conflicting {
- history.extend(self.accessed_info.history.forget(),"accessed",false);
+ifletSome(accessed_info) = self.accessed_info
+ && !accessed_is_conflicting
+{
+ history.extend(accessed_info.history.forget(),"accessed",false);
 }
  history.extend(
 self.conflicting_info.history.extract_relevant(self.error_offset,self.error_kind),
@@ -363,6 +376,20 @@ impl TbError<'_> {
 }
 }
 
+/// Cannot access this allocation with wildcard provenance, as there are no
+/// valid exposed references for this access kind.
+pubfnno_valid_exposed_references_error<'tcx>(
+alloc_id:AllocId,
+offset:u64,
+access_cause:AccessCause,
+) -> InterpErrorKind<'tcx>{
+let title =
+format!("{access_cause} through <wildcard> at {alloc_id:?}[{offset:#x}] is forbidden");
+let details = vec![format!("there are no exposed tags which may perform this access here")];
+let history = HistoryData::default();
+err_machine_stop!(TerminationInfo::TreeBorrowsUb{ title, details, history })
+}
+
 typeS = &'staticstr;
 /// Pretty-printing details
 ///
@@ -623,10 +650,10 @@ impl DisplayRepr {
 }else{
 // We take this node
 let rperm = tree
-.rperms
+.locations
 .iter_all()
-.map(move |(_offset,perms)| {
-let perm = perms.get(idx);
+.map(move |(_offset,loc)| {
+let perm = loc.perms.get(idx);
  perm.cloned()
 })
 .collect::<Vec<_>>();
@@ -788,7 +815,7 @@ impl<'tcx> Tree {
 show_unnamed:bool,
 ) -> InterpResult<'tcx>{
 letmut indenter = DisplayIndent::new();
-let ranges = self.rperms.iter_all().map(|(range,_perms)| range).collect::<Vec<_>>();
+let ranges = self.locations.iter_all().map(|(range,_loc)| range).collect::<Vec<_>>();
 ifletSome(repr) = DisplayRepr::from(self, show_unnamed){
  repr.print(
 &DEFAULT_FORMATTER,

src/tools/miri/src/borrow_tracker/tree_borrows/mod.rs

@@ -14,6 +14,7 @@ mod foreign_access_skipping;
 mod perms;
 mod tree;
 mod unimap;
+mod wildcard;
 
 #[cfg(test)]
 mod exhaustive;
@@ -54,16 +55,10 @@ impl<'tcx> Tree {
  interpret::Pointer::new(alloc_id, range.start),
  range.size.bytes(),
 );
-// TODO: for now we bail out on wildcard pointers. Eventually we should
-// handle them as much as we can.
-let tag = match prov {
-ProvenanceExtra::Concrete(tag) => tag,
-ProvenanceExtra::Wildcard => returninterp_ok(()),
-};
 let global = machine.borrow_tracker.as_ref().unwrap();
 let span = machine.current_user_relevant_span();
 self.perform_access(
-tag,
+prov,
 Some((range, access_kind, diagnostics::AccessCause::Explicit(access_kind))),
  global,
  alloc_id,
@@ -79,19 +74,9 @@ impl<'tcx> Tree {
 size:Size,
 machine:&MiriMachine<'tcx>,
 ) -> InterpResult<'tcx>{
-// TODO: for now we bail out on wildcard pointers. Eventually we should
-// handle them as much as we can.
-let tag = match prov {
-ProvenanceExtra::Concrete(tag) => tag,
-ProvenanceExtra::Wildcard => returninterp_ok(()),
-};
 let global = machine.borrow_tracker.as_ref().unwrap();
 let span = machine.current_user_relevant_span();
-self.dealloc(tag,alloc_range(Size::ZERO, size), global, alloc_id, span)
-}
-
-pubfnexpose_tag(&mutself,_tag:BorTag){
-// TODO
+self.dealloc(prov,alloc_range(Size::ZERO, size), global, alloc_id, span)
 }
 
 /// A tag just lost its protector.
@@ -109,7 +94,11 @@ impl<'tcx> Tree {
 ) -> InterpResult<'tcx>{
 let span = machine.current_user_relevant_span();
 // `None` makes it the magic on-protector-end operation
-self.perform_access(tag,None, global, alloc_id, span)
+self.perform_access(ProvenanceExtra::Concrete(tag),None, global, alloc_id, span)?;
+
+self.update_exposure_for_protector_release(tag);
+
+interp_ok(())
 }
 }
 
@@ -239,21 +228,22 @@ trait EvalContextPrivExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 assert_eq!(ptr_size,Size::ZERO);// we did the deref check above, size has to be 0 here
 // This pointer doesn't come with an AllocId, so there's no
 // memory to do retagging in.
+let new_prov = place.ptr().provenance;
 trace!(
-"reborrow of size 0: reference {:?} derived from {:?} (pointee {})",
- new_tag,
+"reborrow of size 0: reusing {:?} (pointee {})",
  place.ptr(),
  place.layout.ty,
 );
 log_creation(this,None)?;
 // Keep original provenance.
-returninterp_ok(place.ptr().provenance);
+returninterp_ok(new_prov);
 }
 };
+
 log_creation(this,Some((alloc_id, base_offset, parent_prov)))?;
 
 let orig_tag = match parent_prov {
-ProvenanceExtra::Wildcard => returninterp_ok(place.ptr().provenance),// TODO: handle wildcard pointers
+ProvenanceExtra::Wildcard => returninterp_ok(place.ptr().provenance),// TODO: handle retagging wildcard pointers
 ProvenanceExtra::Concrete(tag) => tag,
 };
 
@@ -356,7 +346,7 @@ trait EvalContextPrivExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 };
 
  tree_borrows.perform_access(
-orig_tag,
+parent_prov,
 Some((range_in_alloc,AccessKind::Read, diagnostics::AccessCause::Reborrow)),
  this.machine.borrow_tracker.as_ref().unwrap(),
  alloc_id,
@@ -589,7 +579,11 @@ pub trait EvalContextExt<'tcx>: crate::MiriInterpCxExt<'tcx> {
 // uncovers a non-supported `extern static`.
 let alloc_extra = this.get_alloc_extra(alloc_id)?;
 trace!("Tree Borrows tag {tag:?} exposed in {alloc_id:?}");
- alloc_extra.borrow_tracker_tb().borrow_mut().expose_tag(tag);
+
+let global = this.machine.borrow_tracker.as_ref().unwrap();
+let protected_tags = &global.borrow().protected_tags;
+let protected = protected_tags.contains_key(&tag);
+ alloc_extra.borrow_tracker_tb().borrow_mut().expose_tag(tag, protected);
 }
 AllocKind::Function | AllocKind::VTable | AllocKind::TypeId | AllocKind::Dead => {
 // No tree borrows on these allocations.

src/tools/miri/src/borrow_tracker/tree_borrows/perms.rs

@@ -53,6 +53,7 @@ enum PermissionPriv {
 }
 useself::PermissionPriv::*;
 usesuper::foreign_access_skipping::IdempotentForeignAccess;
+usesuper::wildcard::WildcardAccessLevel;
 
 implPartialOrdforPermissionPriv{
 /// PermissionPriv is ordered by the reflexive transitive closure of
@@ -372,6 +373,23 @@ impl Permission {
 pubfnstrongest_idempotent_foreign_access(&self,prot:bool) -> IdempotentForeignAccess{
 self.inner.strongest_idempotent_foreign_access(prot)
 }
+
+/// Returns the strongest access allowed from a child to this node without
+/// causing UB (only considers possible transitions to this permission).
+pubfnstrongest_allowed_child_access(&self,protected:bool) -> WildcardAccessLevel{
+matchself.inner{
+// Everything except disabled can be accessed by read access.
+Disabled => WildcardAccessLevel::None,
+// Frozen references cannot be written to by a child.
+Frozen => WildcardAccessLevel::Read,
+// If the `conflicted` flag is set, then there was a foreign read
+// during the function call that is still ongoing (still `protected`),
+// this is UB (`noalias` violation).
+ReservedFrz{conflicted:true}if protected => WildcardAccessLevel::Read,
+// Everything else allows writes.
+ _ => WildcardAccessLevel::Write,
+}
+}
 }
 
 implPermTransition{
@@ -772,4 +790,32 @@ mod propagation_optimization_checks {
 );
 }
 }
+
+/// Checks that `strongest_allowed_child_access` correctly
+/// represents which transitions are possible.
+#[test]
+fnstrongest_allowed_child_access(){
+for(permission, protected)in <(Permission,bool)>::exhaustive(){
+let strongest_child_access = permission.strongest_allowed_child_access(protected);
+
+let is_read_valid = Permission::perform_access(
+AccessKind::Read,
+AccessRelatedness::LocalAccess,
+ permission,
+ protected,
+)
+.is_some();
+
+let is_write_valid = Permission::perform_access(
+AccessKind::Write,
+AccessRelatedness::LocalAccess,
+ permission,
+ protected,
+)
+.is_some();
+
+assert_eq!(is_read_valid, strongest_child_access >= WildcardAccessLevel::Read);
+assert_eq!(is_write_valid, strongest_child_access >= WildcardAccessLevel::Write);
+}
+}
 }