Re: AMD Microcode Signature Verification Vulnerability

[trinity pointard <trinity.pointard () gmail com>]

> If an attacker is able to control the hypervisor (necessary to load
> rogue microcode) and the processor microcode, how can the VM trust that
> it is actually verifying that attestation and not being sent down a "oh
> yes it is exactly what you want it to be" garden path?

Attestations are cryptographically signed by the cpu, and meant to be sent
elsewhere and verified remotely. The key used to sign (VCEK) are dependent on
the microcode version, so it shouldn't be possible to forge new-looking
signature with old microcodes (i would hope this hold would someone be able to
decrypt a microcode, though i couldn't find information on that subject).