Re: [PATCH v6 08/42] x86/sev-es: initialize sev_status/features within #VC handler

Borislav Petkov
2021-10-21T17:37:05Z

On Thu, Oct 21, 2021 at 06:12:53PM +0100, Dr. David Alan Gilbert wrote:
> OK, so that bit is 8...21 Eax ext2eax bit 6 page 1-109
>
> then 2.1.5.3 CPUID policy enforcement shows 8...21 EAX as
> 'bitmask'
> 'bits set in the GuestVal must also be set in HostVal.
> This is often applied to feature fields where each bit indicates
> support for a feature'
>
> So that's right isn't it?

Yap, AFAIRC, it would fail the check if:

(GuestVal & HostVal) != GuestVal

and GuestVal is "the CPUID result value created by the hypervisor that
it wants to give to the guest". Let's say it clears bit 6 there.

Then HostVal comes in which is "the actual CPUID result value specified
in this PPR" and there the guest catches the HV lying its *ss off.

:-)

--
Regards/Gruss,
Boris.