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

[Sean Christopherson]

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.