From: Sean Christopherson seanjc@google.com
commit 2aa078932ff6c66bf10cc5b3144440dbfa7d813d upstream.
Return -1 from the get_walk() helpers if the shadow walk doesn't fill at least one spte, which can theoretically happen if the walk hits a not-present PDPTR. Returning the root level in such a case will cause get_mmio_spte() to return garbage (uninitialized stack data). In practice, such a scenario should be impossible as KVM shouldn't get a reserved-bit page fault with a not-present PDPTR.
Note, using mmu->root_level in get_walk() is wrong for other reasons, too, but that's now a moot point.
Fixes: 95fb5b0258b7 ("kvm: x86/mmu: Support MMIO in the TDP MMU") Cc: Ben Gardon bgardon@google.com Cc: stable@vger.kernel.org Signed-off-by: Sean Christopherson seanjc@google.com Message-Id: 20201218003139.2167891-2-seanjc@google.com Signed-off-by: Paolo Bonzini pbonzini@redhat.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- arch/x86/kvm/mmu/mmu.c | 7 ++++++- arch/x86/kvm/mmu/tdp_mmu.c | 2 +- 2 files changed, 7 insertions(+), 2 deletions(-)
--- a/arch/x86/kvm/mmu/mmu.c +++ b/arch/x86/kvm/mmu/mmu.c @@ -3488,7 +3488,7 @@ static bool mmio_info_in_cache(struct kv static int get_walk(struct kvm_vcpu *vcpu, u64 addr, u64 *sptes) { struct kvm_shadow_walk_iterator iterator; - int leaf = vcpu->arch.mmu->root_level; + int leaf = -1; u64 spte;
@@ -3532,6 +3532,11 @@ static bool get_mmio_spte(struct kvm_vcp else leaf = get_walk(vcpu, addr, sptes);
+ if (unlikely(leaf < 0)) { + *sptep = 0ull; + return reserved; + } + rsvd_check = &vcpu->arch.mmu->shadow_zero_check;
for (level = root; level >= leaf; level--) { --- a/arch/x86/kvm/mmu/tdp_mmu.c +++ b/arch/x86/kvm/mmu/tdp_mmu.c @@ -1152,8 +1152,8 @@ int kvm_tdp_mmu_get_walk(struct kvm_vcpu { struct tdp_iter iter; struct kvm_mmu *mmu = vcpu->arch.mmu; - int leaf = vcpu->arch.mmu->shadow_root_level; gfn_t gfn = addr >> PAGE_SHIFT; + int leaf = -1;
tdp_mmu_for_each_pte(iter, mmu, gfn, gfn + 1) { leaf = iter.level;