Fetch KDS cert logic fails on non-Milan machines

[deeglaze]

Describe the bug

fetch_vcek_from_kds is a fallback mechanism when extended guest requests fail to provide a cached VCEK certificate to the guest. The solution in PR #555 hardcodes "Milan" in the endpoint. This will not work for Genoa, Turin, or later products because of the baked-in model string. You can extract the family and model number from attestation report v3 by

family is zen3/zen4 (19h) and map model 0 to "Milan", 1 to "Genoa", or
family is zen5 (1Ah) and map model 2 to "Turin".

How to reproduce

Don't provide cached VCEK to a SEV-SNP VM and verify attestation on Genoa or later.

CoCo version information

latest

What TEE are you seeing the problem on

Snp

Failing command and relevant log output

No response

[Xynnn007]

Are you interested in this? @AdithyaKrishnan

[AdithyaKrishnan]

Yes, I'll create a PR to address this very soon.

[vele-lorica]

Hey guys, I am assuming we need to update to sev 5.0 to enable extracting those values from v3 attestation report? Also, is there any status to resolving this bug?

[deeglaze]

I have this KDS URL derivation logic present in a Go library you can base a solution off https://github.com/google/go-sev-guest/blob/main/verify/verify.go#L742