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Restrict exception fixups to synchronous faults - #1191

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Restrict exception fixups to synchronous faults#1191
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@sangho2Sangho Lee (sangho2) commented Aug 18, 2026

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This PR prevents the exception fixup path from misclassifying asynchronous faults as memory faults. Currently, an asynchronous signal delivered during exception fixup execution is handled as a memory fault, causing memcpy_fallible to abort and the signal to be lost.

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Sangho Lee (sangho2) marked this pull request as ready for review August 18, 2026 17:31
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🤖 SemverChecks 🤖 No breaking API changes detected

Note: this does not mean API is unchanged, or even that there are no breaking changes; simply, none of the detections triggered.

@sangho2Sangho Lee (sangho2) mentioned this pull request Aug 18, 2026
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Claude Opus 5: Found one high-severity issue at litebox_platform_linux_userland/src/lib.rs:2117-2133 .

Opus reports that asynchronous SIGSEGV delivered while in_guest == 1 bypasses the new si_code > 0 guard in next_signal_handler . The handler may therefore construct a guest exception from stale REG_TRAPNO , REG_ERR , and REG_CR2 values, injecting a bogus fault into the guest. The proposed fix is to test synchronicity in exception_signal_handler before calling signal_handler_exit_guest , and route asynchronous signals through the pending/next-handler path. The same concern may apply to SIGBUS , SIGFPE , SIGILL , and SIGTRAP .

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Sangho Lee (sangho2) commented Aug 21, 2026•
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Sangho Lee (Sangho Lee (@sangho2)) is this a valid concern?

Claude Opus 5: Found one high-severity issue at litebox_platform_linux_userland/src/lib.rs:2117-2133 .

Opus reports that asynchronous SIGSEGV delivered while in_guest == 1 bypasses the new si_code > 0 guard in next_signal_handler . The handler may therefore construct a guest exception from stale REG_TRAPNO , REG_ERR , and REG_CR2 values, injecting a bogus fault into the guest. The proposed fix is to test synchronicity in exception_signal_handler before calling signal_handler_exit_guest , and route asynchronous signals through the pending/next-handler path. The same concern may apply to SIGBUS , SIGFPE , SIGILL , and SIGTRAP .

It seems that what Opus found is an interesting bug, but orthogonal to the issue that this PR covers. This PR aims to ensure that memcpy_fallible is not cancelled due to async SIGSEGV. In this case, in_guest must be 0.

Further analysis on async SIGSEGV while in_guest == 1 reveals that LiteBox would deliver it to the guest as a kernel-triggered SIGSEGV at the stale CR2 which cannot be masked (DoS).

#1193

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Restrict exception fixups to synchronous faults by sangho2 · Pull Request #1191 · microsoft/litebox · GitHub
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Restrict exception fixups to synchronous faults - #1191
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sanghle/fix_async_segv
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Restrict exception fixups to synchronous faults#1191
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This PR prevents the exception fixup path from misclassifying asynchronous faults as memory faults. Currently, an asynchronous signal delivered during exception fixup execution is handled as a memory fault, causing memcpy_fallible to abort and the signal to be lost.
@sangho2
Sangho Lee (sangho2)
marked this pull request as ready for review
August 18, 2026 17:31
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🤖 SemverChecks 🤖 No breaking API changes detected
Note: this does not mean API is unchanged, or even that there are no breaking changes; simply, none of the detections triggered.
@sangho2Sangho Lee (sangho2)
mentioned this pull request
Aug 18, 2026

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Sangho Lee (@sangho2) is this a valid concern?
Claude Opus 5: Found one high-severity issue at litebox_platform_linux_userland/src/lib.rs:2117-2133 .
Opus reports that asynchronous SIGSEGV delivered while in_guest == 1 bypasses the new si_code > 0 guard in next_signal_handler . The handler may therefore construct a guest exception from stale REG_TRAPNO , REG_ERR , and REG_CR2 values, injecting a bogus fault into the guest. The proposed fix is to test synchronicity in exception_signal_handler before calling signal_handler_exit_guest , and route asynchronous signals through the pending/next-handler path. The same concern may apply to SIGBUS , SIGFPE , SIGILL , and SIGTRAP .
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Sangho Lee (Sangho Lee (@sangho2)) is this a valid concern?
Claude Opus 5: Found one high-severity issue at litebox_platform_linux_userland/src/lib.rs:2117-2133 .
Opus reports that asynchronous SIGSEGV delivered while in_guest == 1 bypasses the new si_code > 0 guard in next_signal_handler . The handler may therefore construct a guest exception from stale REG_TRAPNO , REG_ERR , and REG_CR2 values, injecting a bogus fault into the guest. The proposed fix is to test synchronicity in exception_signal_handler before calling signal_handler_exit_guest , and route asynchronous signals through the pending/next-handler path. The same concern may apply to SIGBUS , SIGFPE , SIGILL , and SIGTRAP .
It seems that what Opus found is an interesting bug, but orthogonal to the issue that this PR covers. This PR aims to ensure that memcpy_fallible is not cancelled due to async SIGSEGV. In this case, in_guest must be 0.
Further analysis on async SIGSEGV while in_guest == 1 reveals that LiteBox would deliver it to the guest as a kernel-triggered SIGSEGV at the stale CR2 which cannot be masked (DoS).
#1193
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, 'i');
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try {
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var __re = new RegExp('^' + ".*" + '
Restrict exception fixups to synchronous faults by sangho2 · Pull Request #1191 · microsoft/litebox · GitHub
Skip to content
Restrict exception fixups to synchronous faults - #1191
Open
Sangho Lee (sangho2) wants to merge 2 commits into
mainfrom 
sanghle/fix_async_segv
Open
Restrict exception fixups to synchronous faults#1191
Sangho Lee (sangho2) wants to merge 2 commits into
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sanghle/fix_async_segv
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@sangho2Sangho Lee (sangho2)
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This PR prevents the exception fixup path from misclassifying asynchronous faults as memory faults. Currently, an asynchronous signal delivered during exception fixup execution is handled as a memory fault, causing memcpy_fallible to abort and the signal to be lost.
@sangho2
Sangho Lee (sangho2)
marked this pull request as ready for review
August 18, 2026 17:31
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🤖 SemverChecks 🤖 No breaking API changes detected
Note: this does not mean API is unchanged, or even that there are no breaking changes; simply, none of the detections triggered.
@sangho2Sangho Lee (sangho2)
mentioned this pull request
Aug 18, 2026

Open

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Weidong Cui (wdcui)
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Sangho Lee (@sangho2) is this a valid concern?
Claude Opus 5: Found one high-severity issue at litebox_platform_linux_userland/src/lib.rs:2117-2133 .
Opus reports that asynchronous SIGSEGV delivered while in_guest == 1 bypasses the new si_code > 0 guard in next_signal_handler . The handler may therefore construct a guest exception from stale REG_TRAPNO , REG_ERR , and REG_CR2 values, injecting a bogus fault into the guest. The proposed fix is to test synchronicity in exception_signal_handler before calling signal_handler_exit_guest , and route asynchronous signals through the pending/next-handler path. The same concern may apply to SIGBUS , SIGFPE , SIGILL , and SIGTRAP .
@sangho2
Sangho Lee (sangho2)
commented
Aug 21, 2026•

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Sangho Lee (Sangho Lee (@sangho2)) is this a valid concern?
Claude Opus 5: Found one high-severity issue at litebox_platform_linux_userland/src/lib.rs:2117-2133 .
Opus reports that asynchronous SIGSEGV delivered while in_guest == 1 bypasses the new si_code > 0 guard in next_signal_handler . The handler may therefore construct a guest exception from stale REG_TRAPNO , REG_ERR , and REG_CR2 values, injecting a bogus fault into the guest. The proposed fix is to test synchronicity in exception_signal_handler before calling signal_handler_exit_guest , and route asynchronous signals through the pending/next-handler path. The same concern may apply to SIGBUS , SIGFPE , SIGILL , and SIGTRAP .
It seems that what Opus found is an interesting bug, but orthogonal to the issue that this PR covers. This PR aims to ensure that memcpy_fallible is not cancelled due to async SIGSEGV. In this case, in_guest must be 0.
Further analysis on async SIGSEGV while in_guest == 1 reveals that LiteBox would deliver it to the guest as a kernel-triggered SIGSEGV at the stale CR2 which cannot be masked (DoS).
#1193
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, 'i');
if (__m === '*' || __re.test(location.href)) {
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try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '
Restrict exception fixups to synchronous faults by sangho2 · Pull Request #1191 · microsoft/litebox · GitHub
Skip to content
Restrict exception fixups to synchronous faults - #1191
Open
Sangho Lee (sangho2) wants to merge 2 commits into
mainfrom 
sanghle/fix_async_segv
Open
Restrict exception fixups to synchronous faults#1191
Sangho Lee (sangho2) wants to merge 2 commits into
mainfrom 
sanghle/fix_async_segv
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@sangho2Sangho Lee (sangho2)
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This PR prevents the exception fixup path from misclassifying asynchronous faults as memory faults. Currently, an asynchronous signal delivered during exception fixup execution is handled as a memory fault, causing memcpy_fallible to abort and the signal to be lost.
@sangho2
Sangho Lee (sangho2)
marked this pull request as ready for review
August 18, 2026 17:31
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🤖 SemverChecks 🤖 No breaking API changes detected
Note: this does not mean API is unchanged, or even that there are no breaking changes; simply, none of the detections triggered.
@sangho2Sangho Lee (sangho2)
mentioned this pull request
Aug 18, 2026

Open

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Weidong Cui (wdcui)
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Sangho Lee (@sangho2) is this a valid concern?
Claude Opus 5: Found one high-severity issue at litebox_platform_linux_userland/src/lib.rs:2117-2133 .
Opus reports that asynchronous SIGSEGV delivered while in_guest == 1 bypasses the new si_code > 0 guard in next_signal_handler . The handler may therefore construct a guest exception from stale REG_TRAPNO , REG_ERR , and REG_CR2 values, injecting a bogus fault into the guest. The proposed fix is to test synchronicity in exception_signal_handler before calling signal_handler_exit_guest , and route asynchronous signals through the pending/next-handler path. The same concern may apply to SIGBUS , SIGFPE , SIGILL , and SIGTRAP .
@sangho2
Sangho Lee (sangho2)
commented
Aug 21, 2026•

edited

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Sangho Lee (Sangho Lee (@sangho2)) is this a valid concern?
Claude Opus 5: Found one high-severity issue at litebox_platform_linux_userland/src/lib.rs:2117-2133 .
Opus reports that asynchronous SIGSEGV delivered while in_guest == 1 bypasses the new si_code > 0 guard in next_signal_handler . The handler may therefore construct a guest exception from stale REG_TRAPNO , REG_ERR , and REG_CR2 values, injecting a bogus fault into the guest. The proposed fix is to test synchronicity in exception_signal_handler before calling signal_handler_exit_guest , and route asynchronous signals through the pending/next-handler path. The same concern may apply to SIGBUS , SIGFPE , SIGILL , and SIGTRAP .
It seems that what Opus found is an interesting bug, but orthogonal to the issue that this PR covers. This PR aims to ensure that memcpy_fallible is not cancelled due to async SIGSEGV. In this case, in_guest must be 0.
Further analysis on async SIGSEGV while in_guest == 1 reveals that LiteBox would deliver it to the guest as a kernel-triggered SIGSEGV at the stale CR2 which cannot be masked (DoS).
#1193
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, 'i');
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var __m = "youtube.com";
var __re = new RegExp('^' + "youtube\\.com" + '
Restrict exception fixups to synchronous faults by sangho2 · Pull Request #1191 · microsoft/litebox · GitHub
Skip to content
Restrict exception fixups to synchronous faults - #1191
Open
Sangho Lee (sangho2) wants to merge 2 commits into
mainfrom 
sanghle/fix_async_segv
Open
Restrict exception fixups to synchronous faults#1191
Sangho Lee (sangho2) wants to merge 2 commits into
mainfrom 
sanghle/fix_async_segv
Conversation
@sangho2
@sangho2Sangho Lee (sangho2)
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Aug 18, 2026

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This PR prevents the exception fixup path from misclassifying asynchronous faults as memory faults. Currently, an asynchronous signal delivered during exception fixup execution is handled as a memory fault, causing memcpy_fallible to abort and the signal to be lost.
@sangho2
Sangho Lee (sangho2)
marked this pull request as ready for review
August 18, 2026 17:31
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🤖 SemverChecks 🤖 No breaking API changes detected
Note: this does not mean API is unchanged, or even that there are no breaking changes; simply, none of the detections triggered.
@sangho2Sangho Lee (sangho2)
mentioned this pull request
Aug 18, 2026

Open

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Weidong Cui (wdcui)
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Sangho Lee (@sangho2) is this a valid concern?
Claude Opus 5: Found one high-severity issue at litebox_platform_linux_userland/src/lib.rs:2117-2133 .
Opus reports that asynchronous SIGSEGV delivered while in_guest == 1 bypasses the new si_code > 0 guard in next_signal_handler . The handler may therefore construct a guest exception from stale REG_TRAPNO , REG_ERR , and REG_CR2 values, injecting a bogus fault into the guest. The proposed fix is to test synchronicity in exception_signal_handler before calling signal_handler_exit_guest , and route asynchronous signals through the pending/next-handler path. The same concern may apply to SIGBUS , SIGFPE , SIGILL , and SIGTRAP .
@sangho2
Sangho Lee (sangho2)
commented
Aug 21, 2026•

edited

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Sangho Lee (Sangho Lee (@sangho2)) is this a valid concern?
Claude Opus 5: Found one high-severity issue at litebox_platform_linux_userland/src/lib.rs:2117-2133 .
Opus reports that asynchronous SIGSEGV delivered while in_guest == 1 bypasses the new si_code > 0 guard in next_signal_handler . The handler may therefore construct a guest exception from stale REG_TRAPNO , REG_ERR , and REG_CR2 values, injecting a bogus fault into the guest. The proposed fix is to test synchronicity in exception_signal_handler before calling signal_handler_exit_guest , and route asynchronous signals through the pending/next-handler path. The same concern may apply to SIGBUS , SIGFPE , SIGILL , and SIGTRAP .
It seems that what Opus found is an interesting bug, but orthogonal to the issue that this PR covers. This PR aims to ensure that memcpy_fallible is not cancelled due to async SIGSEGV. In this case, in_guest must be 0.
Further analysis on async SIGSEGV while in_guest == 1 reveals that LiteBox would deliver it to the guest as a kernel-triggered SIGSEGV at the stale CR2 which cannot be masked (DoS).
#1193
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, 'i');
if (__m === '*' || __re.test(location.href)) {
// Auto-enable theater mode on YouTube
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function tryTheater() {
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} catch(__e) { console.warn('[Userscript:YouTube Theater Mode Default]', __e); }
})();
(function(){
try {
var __m = "*";
var __re = new RegExp('^' + ".*" + '
Restrict exception fixups to synchronous faults by sangho2 · Pull Request #1191 · microsoft/litebox · GitHub
Skip to content
Restrict exception fixups to synchronous faults - #1191
Open
Sangho Lee (sangho2) wants to merge 2 commits into
mainfrom 
sanghle/fix_async_segv
Open
Restrict exception fixups to synchronous faults#1191
Sangho Lee (sangho2) wants to merge 2 commits into
mainfrom 
sanghle/fix_async_segv
Conversation
@sangho2
@sangho2Sangho Lee (sangho2)
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Aug 18, 2026

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This PR prevents the exception fixup path from misclassifying asynchronous faults as memory faults. Currently, an asynchronous signal delivered during exception fixup execution is handled as a memory fault, causing memcpy_fallible to abort and the signal to be lost.
@sangho2
Sangho Lee (sangho2)
marked this pull request as ready for review
August 18, 2026 17:31
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🤖 SemverChecks 🤖 No breaking API changes detected
Note: this does not mean API is unchanged, or even that there are no breaking changes; simply, none of the detections triggered.
@sangho2Sangho Lee (sangho2)
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Sangho Lee (@sangho2) is this a valid concern?
Claude Opus 5: Found one high-severity issue at litebox_platform_linux_userland/src/lib.rs:2117-2133 .
Opus reports that asynchronous SIGSEGV delivered while in_guest == 1 bypasses the new si_code > 0 guard in next_signal_handler . The handler may therefore construct a guest exception from stale REG_TRAPNO , REG_ERR , and REG_CR2 values, injecting a bogus fault into the guest. The proposed fix is to test synchronicity in exception_signal_handler before calling signal_handler_exit_guest , and route asynchronous signals through the pending/next-handler path. The same concern may apply to SIGBUS , SIGFPE , SIGILL , and SIGTRAP .
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Sangho Lee (Sangho Lee (@sangho2)) is this a valid concern?
Claude Opus 5: Found one high-severity issue at litebox_platform_linux_userland/src/lib.rs:2117-2133 .
Opus reports that asynchronous SIGSEGV delivered while in_guest == 1 bypasses the new si_code > 0 guard in next_signal_handler . The handler may therefore construct a guest exception from stale REG_TRAPNO , REG_ERR , and REG_CR2 values, injecting a bogus fault into the guest. The proposed fix is to test synchronicity in exception_signal_handler before calling signal_handler_exit_guest , and route asynchronous signals through the pending/next-handler path. The same concern may apply to SIGBUS , SIGFPE , SIGILL , and SIGTRAP .
It seems that what Opus found is an interesting bug, but orthogonal to the issue that this PR covers. This PR aims to ensure that memcpy_fallible is not cancelled due to async SIGSEGV. In this case, in_guest must be 0.
Further analysis on async SIGSEGV while in_guest == 1 reveals that LiteBox would deliver it to the guest as a kernel-triggered SIGSEGV at the stale CR2 which cannot be masked (DoS).
#1193
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Restrict exception fixups to synchronous faults by sangho2 · Pull Request #1191 · microsoft/litebox · GitHub
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Restrict exception fixups to synchronous faults - #1191
Open
Sangho Lee (sangho2) wants to merge 2 commits into
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sanghle/fix_async_segv
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Restrict exception fixups to synchronous faults#1191
Sangho Lee (sangho2) wants to merge 2 commits into
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sanghle/fix_async_segv
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@sangho2Sangho Lee (sangho2)
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This PR prevents the exception fixup path from misclassifying asynchronous faults as memory faults. Currently, an asynchronous signal delivered during exception fixup execution is handled as a memory fault, causing memcpy_fallible to abort and the signal to be lost.
@sangho2
Sangho Lee (sangho2)
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August 18, 2026 17:31
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🤖 SemverChecks 🤖 No breaking API changes detected
Note: this does not mean API is unchanged, or even that there are no breaking changes; simply, none of the detections triggered.
@sangho2Sangho Lee (sangho2)
mentioned this pull request
Aug 18, 2026

Open

@wdcui
Weidong Cui (wdcui)
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Aug 21, 2026

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Sangho Lee (@sangho2) is this a valid concern?
Claude Opus 5: Found one high-severity issue at litebox_platform_linux_userland/src/lib.rs:2117-2133 .
Opus reports that asynchronous SIGSEGV delivered while in_guest == 1 bypasses the new si_code > 0 guard in next_signal_handler . The handler may therefore construct a guest exception from stale REG_TRAPNO , REG_ERR , and REG_CR2 values, injecting a bogus fault into the guest. The proposed fix is to test synchronicity in exception_signal_handler before calling signal_handler_exit_guest , and route asynchronous signals through the pending/next-handler path. The same concern may apply to SIGBUS , SIGFPE , SIGILL , and SIGTRAP .
@sangho2
Sangho Lee (sangho2)
commented
Aug 21, 2026•

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Sangho Lee (Sangho Lee (@sangho2)) is this a valid concern?
Claude Opus 5: Found one high-severity issue at litebox_platform_linux_userland/src/lib.rs:2117-2133 .
Opus reports that asynchronous SIGSEGV delivered while in_guest == 1 bypasses the new si_code > 0 guard in next_signal_handler . The handler may therefore construct a guest exception from stale REG_TRAPNO , REG_ERR , and REG_CR2 values, injecting a bogus fault into the guest. The proposed fix is to test synchronicity in exception_signal_handler before calling signal_handler_exit_guest , and route asynchronous signals through the pending/next-handler path. The same concern may apply to SIGBUS , SIGFPE , SIGILL , and SIGTRAP .
It seems that what Opus found is an interesting bug, but orthogonal to the issue that this PR covers. This PR aims to ensure that memcpy_fallible is not cancelled due to async SIGSEGV. In this case, in_guest must be 0.
Further analysis on async SIGSEGV while in_guest == 1 reveals that LiteBox would deliver it to the guest as a kernel-triggered SIGSEGV at the stale CR2 which cannot be masked (DoS).
#1193
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, 'i');
if (__m === '*' || __re.test(location.href)) {
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} catch(__e) { console.warn('[Userscript:Universal Dark Mode]', __e); }
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Restrict exception fixups to synchronous faults by sangho2 · Pull Request #1191 · microsoft/litebox · GitHub
Skip to content
Restrict exception fixups to synchronous faults - #1191
Open
Sangho Lee (sangho2) wants to merge 2 commits into
mainfrom 
sanghle/fix_async_segv
Open
Restrict exception fixups to synchronous faults#1191
Sangho Lee (sangho2) wants to merge 2 commits into
mainfrom 
sanghle/fix_async_segv
Conversation
@sangho2
@sangho2Sangho Lee (sangho2)
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Aug 18, 2026

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This PR prevents the exception fixup path from misclassifying asynchronous faults as memory faults. Currently, an asynchronous signal delivered during exception fixup execution is handled as a memory fault, causing memcpy_fallible to abort and the signal to be lost.
@sangho2
Sangho Lee (sangho2)
marked this pull request as ready for review
August 18, 2026 17:31
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🤖 SemverChecks 🤖 No breaking API changes detected
Note: this does not mean API is unchanged, or even that there are no breaking changes; simply, none of the detections triggered.
@sangho2Sangho Lee (sangho2)
mentioned this pull request
Aug 18, 2026

Open

@wdcui
Weidong Cui (wdcui)
commented
Aug 21, 2026

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Sangho Lee (@sangho2) is this a valid concern?
Claude Opus 5: Found one high-severity issue at litebox_platform_linux_userland/src/lib.rs:2117-2133 .
Opus reports that asynchronous SIGSEGV delivered while in_guest == 1 bypasses the new si_code > 0 guard in next_signal_handler . The handler may therefore construct a guest exception from stale REG_TRAPNO , REG_ERR , and REG_CR2 values, injecting a bogus fault into the guest. The proposed fix is to test synchronicity in exception_signal_handler before calling signal_handler_exit_guest , and route asynchronous signals through the pending/next-handler path. The same concern may apply to SIGBUS , SIGFPE , SIGILL , and SIGTRAP .
@sangho2
Sangho Lee (sangho2)
commented
Aug 21, 2026•

edited

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Sangho Lee (Sangho Lee (@sangho2)) is this a valid concern?
Claude Opus 5: Found one high-severity issue at litebox_platform_linux_userland/src/lib.rs:2117-2133 .
Opus reports that asynchronous SIGSEGV delivered while in_guest == 1 bypasses the new si_code > 0 guard in next_signal_handler . The handler may therefore construct a guest exception from stale REG_TRAPNO , REG_ERR , and REG_CR2 values, injecting a bogus fault into the guest. The proposed fix is to test synchronicity in exception_signal_handler before calling signal_handler_exit_guest , and route asynchronous signals through the pending/next-handler path. The same concern may apply to SIGBUS , SIGFPE , SIGILL , and SIGTRAP .
It seems that what Opus found is an interesting bug, but orthogonal to the issue that this PR covers. This PR aims to ensure that memcpy_fallible is not cancelled due to async SIGSEGV. In this case, in_guest must be 0.
Further analysis on async SIGSEGV while in_guest == 1 reveals that LiteBox would deliver it to the guest as a kernel-triggered SIGSEGV at the stale CR2 which cannot be masked (DoS).
#1193
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