Explicit SNP platform requirements¶

A signed report establishes authenticity. A relying party must separately decide which reported platform settings it accepts. The Python verifier can enforce that choice for native AMD SEV-SNP and Azure vTPM-rooted SEV-SNP evidence:

from cmcp_verify import SnpPlatformPolicy, verify_trace_claim

platform_policy = SnpPlatformPolicy(
    require=frozenset({
        "ciphertext_hiding_dram_enabled",
        "alias_check_complete",
    }),
    forbid=frozenset({"smt_enabled"}),
    reject_unrecognized_bits=True,
)
result = verify_trace_claim(
    claim,
    approved,
    trusted_ark_pem=pinned_amd_root,
    snp_platform_policy=platform_policy,
)

This example is an explicit policy choice, not a universal safe-platform profile. It may reject available hardware. Do not weaken it merely to obtain a passing result without reconsidering the adversary model. require names fields that must be true; forbid names fields that must be false. Supported field names are those of agent_manifest.PLATFORM_INFO_BITS. Unknown names, contradictory requirements, and malformed policy values are configuration errors.

The policy belongs to the verifier. Do not deserialize it from untrusted claim content and treat it as the relying party's decision. It is immutable after construction, including when initialized from a mutable set.

Acceptance and rejection¶

The verifier checks the pinned chain and report signature before appraising the signed PLATFORM_INFO word. The native SNP and Azure CVM standalone APIs accept the same object as platform_policy=. A supplied policy, including an empty one, requires authenticated SNP evidence. Missing roots, missing evidence, and claims selecting a non-SNP or software provider cannot bypass the requirement.

An unmet policy sets failure_reason on the public verification result to HARDWARE_ATTESTATION_FAILED, records the detail, and never returns VERIFIED. A result can retain PARTIALLY_VERIFIED status for unrelated successful checks; it is not permission to release data. Require no failure, VERIFIED status, and platform_state in verified_fields for this particular gate.

Successful appraisal records platform_state and the authenticated raw word in details["platform_info"]. Omitting the policy preserves previous behavior and does not assert platform state. The CLI and gateway startup do not configure this policy; applications calling the Python verifier must supply it.

Limits¶

This check covers only SNP PLATFORM_INFO. It does not cover the separate guest POLICY word (including debug mode), minimum TCB versions, revocation, workload correctness, key residency, CPU/GPU channel protection, or remote tools. It is an offline evidence check, not proof of current liveness. Protect data only after the complete admission policy, including freshness and channel binding, passes.

tests/unit/test_snp_platform_policy.py exercises signed synthetic reports with acceptable settings, missing required bits, forbidden bits, unknown bits, missing trust roots, tampered platform state, and provider downgrade attempts. The tests exercise real cryptographic verification with a synthetic PKI. They do not constitute a new live hardware demonstration.