Sean Christopherson <seanjc@xxxxxxxxxx> writes:
> 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 PTPDR. Returning the root level in such a case will cause
PDPTR
> 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@xxxxxxxxxx>
> Cc: stable@xxxxxxxxxxxxxxx
> Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
> ---
> arch/x86/kvm/mmu/mmu.c | 7 ++++++-
> arch/x86/kvm/mmu/tdp_mmu.c | 2 +-
> 2 files changed, 7 insertions(+), 2 deletions(-)
>
> diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
> index 7a6ae9e90bd7..a48cd12c01d7 100644
> --- 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 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;
> + }
When SPTE=0 is returned from get_mmio_spte(), handle_mmio_page_fault()
will return RET_PF_RETRY -- should it be RET_PF_INVALID instead?
> +
> rsvd_check = &vcpu->arch.mmu->shadow_zero_check;
>
> for (level = root; level >= leaf; level--) {
> diff --git a/arch/x86/kvm/mmu/tdp_mmu.c b/arch/x86/kvm/mmu/tdp_mmu.c
> index 84c8f06bec26..50cec7a15ddb 100644
> --- 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 *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;
--
Vitaly
