cpu/aarch64/windows: Use libstd instead of windows_sys.

[briansmith]

Eliminate the windows-sys dependency on Aarch64. We believe there is no use for no_std support for this target.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 95.70%. Comparing base (03b223d) to head (237424b).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2570      +/-   ##
==========================================
- Coverage   96.56%   95.70%   -0.86%     
==========================================
  Files         181      181              
  Lines       19799    19799              
  Branches      504      504              
==========================================
- Hits        19119    18949     -170     
- Misses        571      715     +144     
- Partials      109      135      +26     

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[complexspaces]

Hey there, I wanted to follow up a point mentioned in the PR description:

We believe there is no use for no_std support for this target.

My current belief is that this isn't fully accurate. Microsoft is releasing VBS enclaves for Windows 11, which run .dll code inside a stripped down/restricted environment. As per MS's public dev guide, they use their own CRT as well:

Enclaves have their own versions of platform, startup, runtime and UCRT libs.

ring dropping support for no_std Windows would prohibit its use in these enclave builds. If you're just looking to remove the windows-sys dependency, I'd recommend switching to windows-bindgen and/or windows-link since ring only uses 2 symbols from the Win32 headers.

[briansmith]

Thanks. What is the target triple for VBS enclaves?

[complexspaces]

To my knowledge the target triples are identical, the only differences is the libs and flags passed to the linker. This blog mentions a Rust-based PoC someone at MS put together. I don't see any non-standard Rust targets in the repository. It only uses those flags and #![no_std] in lib.rs.

[briansmith]

Does IsProcessorFeaturePresent report AES features being available in an enclave?

I wonder if there is some way we could run the tests in an enclave in CI?

[complexspaces]

I don't have an enclave dev environment set up at this moment, sorry, but I can get back to you later on checking if IsProcessorFeaturePresent functions correctly in the enclave.

I wonder if there is some way we could run the tests in an enclave in CI?

I don't believe it'd be possible today for several reasons, at least on GitHub-hosted CI. It requires VBS features to be enabled (which means the Windows host for the test code to run on needs to be able to do virtualization) and it needs a bleeding edge Windows 11 release. Everything else seems workable long-term but I think the nested virtualization would be an issue.