Use TAV for SNP attestation verification

[cjen1-msft]

Stack

• Depends on Vendor TAV 1.0.3 #8067. Do not merge this PR before the vendor PR.
• Integration-only comparison: cjen1-msft/CCF@tee-attestation-verification-tav...tee-attestation-integration-tav

Summary

• add the OpenSSL-backed TAV FFI crate to the ccf-rs umbrella
• replace PAL SNP certificate-chain, report-signature, and TCB verification with tav_verify_snp_attestation
• retain the existing CCF SNP report type, report accessors, and CCF-specific policy checks
• defer migration of report ownership and accessors to a later change

Testing

• Rust 1.90 locked release umbrella build and tav_verify_snp_attestation symbol check
• snp_attestation_test (12 cases, 49 assertions)
• ccf target build
• CMake and C++ formatting
• copyright, ASCII, public include, and diff checks
• independent verifier correctness and MVP scope reviews

[Copilot]

Pull request overview

This PR integrates the TEE Attestation Verification (TAV) FFI crate into CCF’s Rust umbrella (ccf-rs) and switches SEV-SNP attestation verification in the PAL layer to use tav_verify_snp_attestation, while keeping CCF’s existing report parsing and policy checks.

Changes:

• Add the TAV FFI crate to ccf-rs and update the locked Rust dependency graph.
• Replace PAL-side SNP certificate-chain, signature, and TCB verification logic with a TAV verification call and map failures to CCF errors.
• Update SEV-SNP attestation validation tests and build system wiring (Rust build deps, PAL include/link settings).

Custom instructions used:

• .github/copilot-instructions.md
• .github/instructions/reviewing.instructions.md

Reviewed changes

Copilot reviewed 7 out of 8 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/rust/src/lib.rs	Re-exports the new TAV FFI crate from the ccf-rs umbrella.
src/rust/Cargo.toml	Adds the vendored tee-attestation-verification-ffi dependency with OpenSSL crypto feature.
src/rust/Cargo.lock	Locks new transitive dependencies introduced by TAV integration.
src/pal/test/snp_attestation_validation.cpp	Adds/updates negative tests to expect TAV failure paths and error codes.
src/pal/tav_ffi.h	Introduces RAII wrappers for TAV error/report handles used by PAL.
src/pal/attestation.cpp	Replaces local SNP chain/signature verification with tav_verify_snp_attestation and consistent error reporting.
CMakeLists.txt	Updates ccf_pal link libraries and adds include path for TAV FFI headers.
cmake/ccf_rs.cmake	Ensures the Rust build target reruns when the vendored TAV FFI Cargo.toml changes.