sandbox-tee: check a TDX quote's PCK chain to a pinned Intel root #415
2026-10-21
sandbox-tee: check a TDX quote's PCK chain to a pinned Intel root
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#399 made verify_tdx trust only a PCK key the verifier pins, but left pinning it to the deployment: a hand pin, with nothing checking the quote's certificate chain to Intel's root. The SEV-SNP side has amd_kds for exactly this. intel_pcs (feature `intel-pcs`): - verify_pck_chain(trusted_root_der, chain_pem, now_unix) checks the chain a quote carries, the PCK leaf then its issuing CA, optionally ending in the root, to the pinned root. It checks: - ECDSA-P256-SHA256 signatures, with the X.509 (r, s) decoded via der; - the declared algorithm; - issuer and subject names linking up the chain; - each certificate valid at now. A presented root must equal the pinned one byte for byte; a longer chain is refused. It returns the PCK key, the TeeAnchor::Tdx a quote is verified by. - pck_from_quote derives that anchor from the quote's own chain, checked to the root. The trust comes from the root, never from the quote. - Revocation lists are the deployment's to consult, as stated in the module. tdx: TdxQuote::pck_chain(); local_quote takes optional certification data, so a software quote can carry a real chain. CI: the sandbox-rs job now runs `cargo test -p sandbox-tee --features amd-kds,intel-pcs`. The amd-kds tests had never run in CI: a plain `cargo test` does not enable the feature. SPEC §7.6 and the §9 readiness row say the chain is checked. Tests: 5, against a self-generated chain of Intel's structure: - a chain to the pinned root yields the PCK, with or without the root; - a chain to another root is refused, pinned or presented; - every link must hold (a forged leaf or CA, a misnamed issuer, a missing CA, a chain too long, a relabeled algorithm); - a chain outside its validity is refused; - the anchor from a quote's chain verifies that quote and no other root yields one. Mutation testing: 10 mutants, all killed. Verified on the build host: sandbox-tee with amd-kds and intel-pcs, 51 tests; the sandbox workspace, 434; clippy -D warnings clean. Repo checks pass, including workflow concurrency and lockfiles. Co-Authored-By: Claude Opus 5.5 <[email protected]>