Re: [PATCH] KVM: x86: Add GPA limit check to kvm_arch_vcpu_pre_fault_memory()

[Isaku Yamahata]

On Tue, Jul 16, 2024 at 04:49:00PM -0700,
Isaku Yamahata <isaku.yamahata@xxxxxxxxx> wrote:

> > > - For non-TDX case (DEFAULT_VM, SW_PROTECTED_VM, or SEV):
> > >   When the host supports 5-level TDP, KVM decides to use 4-level TDP if
> > >   cpuid_maxphyaddr() <= 48.  cpuid_maxhyaddr() check prevents
> > >   KVM_PRE_FAULT_MEMORY from passing GFN beyond mappable GFN.
> > 
> > Hardening against cpuid_maxphyaddr() should be out of scope.  We don't enforce
> > it for guest faults, e.g. KVM doesn't kill the guest if allow_smaller_maxphyaddr
> > is false and the GPA is supposed to be illegal.  And trying to enforce it here is
> > a fool's errand since userspace can simply do KVM_SET_CPUID2 to circumvent the
> > restriction.
> 
> Ok, I'll drop maxphys addr check.

Now Rick added a patch to check aliased GFN.  This patch and per-VM mmu_max_gfn
become unnecessarily.  Now I come up with update to pre_fault to test no
memslot case.
https://lore.kernel.org/kvm/20240718211230.1492011-19-rick.p.edgecombe@xxxxxxxxx/

For non-x86 case, I'm not sure if we can expect what error.