LVI hardening tests

[raoulstrackx]

Mitigating the speculative execution LVI attack against SGX enclaves requires compiler changes (i.e., adding lfences). This pull requests adds various tests to check if this happens correctly.

[rust-highfive]

r? @Mark-Simulacrum

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[Mark-Simulacrum]

It looks like some of this is testing C and C++ LVI, as well, which seems a bit out of place for this repository? Could you elaborate why those tests are added?

[raoulstrackx]

For the x86_64-fortanix-unknown-sgx target it is important that all code is hardened that will end up in an SGX enclave. Unfortunately, crates may include assembly, C, C++ code as well that needs to be hardened. We need to check if this is done properly.
Assembly code is certainly compiled as part of the standard library, C/C++ code may not be.

[Mark-Simulacrum]

Okay, I think this is reasonable. It's not too many additional tests and they're SGX only so I'm not too worried in that respect either.

@bors r+ rollup=iffy

[bors]

📌 Commit 159d11f has been approved by Mark-Simulacrum

[bors]

⌛ Testing commit 159d11f with merge 032ab1893ec16166331dc85d0b56456bf5442a39...

[rust-log-analyzer]

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[bors]

💔 Test failed - checks-actions

[kennytm]

@bors retry

https://github.com/rust-lang-ci/rust/runs/1169263815i686-msvc-2 failed to download clang.

curl: (56) OpenSSL SSL_read: Connection was reset, errno 10054

[bors]

⌛ Testing commit 159d11f with merge 6369a98...

[bors]

☀️ Test successful - checks-actions, checks-azure
Approved by: Mark-Simulacrum
Pushing 6369a98 to master...