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KVM: x86/mmu: Use -1 to flag an undefined spte in get_mmio_spte()

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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: 95fb5b0258 ("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>
This commit is contained in:
Sean Christopherson 2020-12-17 16:31:36 -08:00 committed by Paolo Bonzini
parent 2c85ebc57b
commit 2aa078932f
2 changed files with 7 additions and 2 deletions
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7
arch/x86/kvm/mmu/mmu.c
View File

@ -3488,7 +3488,7 @@ static bool mmio_info_in_cache(struct kvm_vcpu *vcpu, u64 addr, bool direct)
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_vcpu *vcpu, u64 addr, u64 *sptep)
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--) {

2
arch/x86/kvm/mmu/tdp_mmu.c
View File

@ -1152,8 +1152,8 @@ int kvm_tdp_mmu_get_walk(struct kvm_vcpu *vcpu, u64 addr, u64 *sptes)
{
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;