Re: [RFC PATCH V6 01/14] x86/sev: Add a #HV exception handler

[Tom Lendacky]

On 5/30/23 09:35, Peter Zijlstra wrote:
> On Tue, May 30, 2023 at 02:16:55PM +0200, Gupta, Pankaj wrote:
> > > > Add a #HV exception handler that uses IST stack.
> > >
> > > Urgh.. that is entirely insufficient. Like it doesn't even begin to
> > > start to cover things.
> > >
> > > The whole existing VC IST stack abuse is already a nightmare and you're
> > > duplicating that.. without any explanation for why this would be needed
> > > and how it is correct.
> > >
> > > Please try again.
> >
> > #HV handler handles both #NMI & #MCE in the guest and nested #HV is never
> > raised by the hypervisor.
>
> I thought all this confidental computing nonsense was about not trusting
> the hypervisor, so how come we're now relying on the hypervisor being
> sane?

That should really say that a nested #HV should never be raised by the 
hypervisor, but if it is, then the guest should detect that and 
self-terminate knowing that the hypervisor is possibly being malicious.

Thanks,
Tom