fix(dstack-mr): lower the SEV-SNP metadata page budget to 65536 pages - #1252
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… firmware needs MAX_OVMF_METADATA_PAGES admitted 16777216 pages -- 64 GiB. Every page is one SHA-384 over a PAGE_INFO, and verify_sev_launch recomputes the whole measurement *before* comparing it with the hardware MEASUREMENT, so the budget is spent entirely on input the requester authored. The document is bound only to vm_config.os_image_hash, which the requester also chooses, so no allowlist rejects it first. Measured on an EPYC-class host: 0.68 us per page, so the ceiling is **11.3 seconds of one core** for a measurement.snp.cbor of about 200 bytes. The path is reached from the verifier's POST /verify and from the KMS's key-release path, both gated only by one valid SNP quote -- which a holder can replay with an arbitrary vm_config. The shipped dstack-0.6.0 image declares 7 sections totalling **31 pages**, so the ceiling was 541000x what a real firmware asks for. Lower it to 65536 pages: over 2000x headroom, about 44 ms at the ceiling, and deliberately the same number as tdvf::MAX_MEASURED_PAGES, since the two measurement paths have the same shape and should have the same bound.
This was referenced Sep 20, 2026
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Extend the SEV-SNP case with the certificate-table, empty-report, guest feature, rootfs-hash and page-budget tests (#1248, #1279, #1275, #1252), and the cloud TPM case with the PCR bank, duplicate index, quoted event log, collateral budget and host allowlist tests (#1275, #1267, #1338, Signed-off-by: Kevin Wang <wy721@qq.com> #1238, #1404).
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Problem
MAX_OVMF_METADATA_PAGESallowed 16 777 216 pages (64 GiB). Each page costs a SHA-384, andverify_sev_launchrecomputes the whole measurement from the caller-suppliedmeasurement.snp.cborbefore comparing it with the hardwareMEASUREMENT. A ~200-byte document with one section sized to the budget costs 11.3 s of one core (measured, 0.68 µs/page) on the verifier'sPOST /verifyand the KMS key-release path, repeatable by anyone holding one valid SNP quote.Fix
Lower the ceiling to 65 536 pages, the same bound as
tdvf::MAX_MEASURED_PAGES. The shippeddstack-0.6.0metadata is 7 sections / 31 pages, so this leaves >2000x headroom (~44 ms worst case).Verification
cargo test -p dstack-mrpasses; KMS SNP tests (cargo test -p dstack-kms snp, 14) pass; fmt and clippy clean.