Re: [Question PATCH kernel] x86/amd/sev/nmi+vc: Fix stack handling (why is this happening?)

[Sean Christopherson]

On Tue, Jan 31, 2023, Joerg Roedel wrote:
> On Tue, Jan 31, 2023 at 03:53:39PM +0000, Sean Christopherson wrote:
> > I don't think that is technically true.  A _well-behaved_ hypervisor will not
> > intercept DR0-DR6 accesses for SEV-ES guests, but AFAICT nothing in the SEV-ES
> > architecture enforces that behavior.
> 
> Not from the hardware architecture side, but the GHCB spec does not
> list NAE events for DR0-DR6 accesses, so a guest is not required to
> handle them in the VC handler.
> 
> Linux under SEV-ES will crash if the HV intercepts debug registers,
> except DR7.

Right, I'm just objecting to the wording of "DR0-DR6 are not intercepted".  E.g.
from a security perspective, the kernel shouldn't rely on DR0-DR6 to execute
cleanly.