From: David Matlack dmatlack@google.com
commit 7c8a4742c4abe205ec9daf416c9d42fd6b406e8e upstream.
When the TDP MMU is write-protection GFNs for page table protection (as opposed to for dirty logging, or due to the HVA not being writable), it checks if the SPTE is already write-protected and if so skips modifying the SPTE and the TLB flush.
This behavior is incorrect because it fails to check if the SPTE is write-protected for page table protection, i.e. fails to check that MMU-writable is '0'. If the SPTE was write-protected for dirty logging but not page table protection, the SPTE could locklessly be made writable, and vCPUs could still be running with writable mappings cached in their TLB.
Fix this by only skipping setting the SPTE if the SPTE is already write-protected *and* MMU-writable is already clear. Technically, checking only MMU-writable would suffice; a SPTE cannot be writable without MMU-writable being set. But check both to be paranoid and because it arguably yields more readable code.
Fixes: 46044f72c382 ("kvm: x86/mmu: Support write protection for nesting in tdp MMU") Cc: stable@vger.kernel.org Signed-off-by: David Matlack dmatlack@google.com Message-Id: 20220113233020.3986005-2-dmatlack@google.com Reviewed-by: Sean Christopherson seanjc@google.com Signed-off-by: Paolo Bonzini pbonzini@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- arch/x86/kvm/mmu/tdp_mmu.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-)
--- a/arch/x86/kvm/mmu/tdp_mmu.c +++ b/arch/x86/kvm/mmu/tdp_mmu.c @@ -1493,12 +1493,12 @@ static bool write_protect_gfn(struct kvm !is_last_spte(iter.old_spte, iter.level)) continue;
- if (!is_writable_pte(iter.old_spte)) - break; - new_spte = iter.old_spte & ~(PT_WRITABLE_MASK | shadow_mmu_writable_mask);
+ if (new_spte == iter.old_spte) + break; + tdp_mmu_set_spte(kvm, &iter, new_spte); spte_set = true; }