Re: [PATCH] KVM: nVMX: Prevent vmlaunch with EPTP pointing outside assigned memory area

[Yuan Yao]

On Fri, Jun 30, 2023 at 08:37:06AM -0700, Sean Christopherson wrote:
> On Fri, Jun 30, 2023, Yuan Yao wrote:
> > On Thu, Jun 29, 2023 at 01:30:31PM -0700, Sean Christopherson wrote:
> > > @@ -3834,8 +3822,8 @@ static int mmu_alloc_shadow_roots(struct kvm_vcpu *vcpu)
> > >  			if (!(pdptrs[i] & PT_PRESENT_MASK))
> > >  				continue;
> > >
> > > -			if (mmu_check_root(vcpu, pdptrs[i] >> PAGE_SHIFT))
> > > -				return 1;
> > > +			if (kvm_vcpu_is_visible_gfn(vcpu, pdptrs[i] >> PAGE_SHIFT))
> > > +				pdptrs[i] = 0;
> >
> > Hi Sean,
> >
> > Should this be "!kvm_vcpu_is_visible_gfn(vcpu, pdptrs[i] >> PAGE_SHIFT)" and
>
> Yep, typo that inverted the check.  Thanks for saving me some debug time!
>
> > turn the pae_root[i] to dummy root yet ?
>
> No, zeroing the PDPTR is sufficient.  Unlike CR3, which is always "present", PDPTRs
> have a present bit and so KVM can communicate to hardware that the entry isn't
> valid simply by clearing the PDPTPR.

Got it, same as how KVM deal with other middle level entries,
thanks for the explanation!