[PATCH] KVM: x86/mmu: Verify shadow walk doesn't terminate early in page faults
From: Sean Christopherson
Date: Thu Aug 12 2021 - 11:38:35 EST
WARN and bail if the shadow walk for faulting in a SPTE terminates early,
i.e. doesn't reach the expected level because the walk encountered a
terminal SPTE. The shadow walks for page faults are subtle in that they
install non-leaf SPTEs (zapping leaf SPTEs if necessary!) in the loop
body, and consume the newly created non-leaf SPTE in the loop control,
e.g. __shadow_walk_next(). In other words, the walks guarantee that the
walk will stop if and only if the target level is reached by installing
non-leaf SPTEs to guarantee the walk remains valid.
Opportunistically use fault->goal-level instead of it.level in
FNAME(fetch) to further clarify that KVM always installs the leaf SPTE at
the target level.
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
arch/x86/kvm/mmu/mmu.c | 3 +++
arch/x86/kvm/mmu/paging_tmpl.h | 7 +++++--
2 files changed, 8 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index a272ccbddfa1..2a243ae1d64c 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -2992,6 +2992,9 @@ static int __direct_map(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault)
account_huge_nx_page(vcpu->kvm, sp);
}
+ if (WARN_ON_ONCE(it.level != fault->goal_level))
+ return -EFAULT;
+
ret = mmu_set_spte(vcpu, it.sptep, ACC_ALL,
fault->write, fault->goal_level, base_gfn, fault->pfn,
fault->prefault, fault->map_writable);
diff --git a/arch/x86/kvm/mmu/paging_tmpl.h b/arch/x86/kvm/mmu/paging_tmpl.h
index f70afecbf3a2..3a8a7b2f9979 100644
--- a/arch/x86/kvm/mmu/paging_tmpl.h
+++ b/arch/x86/kvm/mmu/paging_tmpl.h
@@ -749,9 +749,12 @@ static int FNAME(fetch)(struct kvm_vcpu *vcpu, struct kvm_page_fault *fault,
}
}
+ if (WARN_ON_ONCE(it.level != fault->goal_level))
+ return -EFAULT;
+
ret = mmu_set_spte(vcpu, it.sptep, gw->pte_access, fault->write,
- it.level, base_gfn, fault->pfn, fault->prefault,
- fault->map_writable);
+ fault->goal_level, base_gfn, fault->pfn,
+ fault->prefault, fault->map_writable);
if (ret == RET_PF_SPURIOUS)
return ret;
--
2.33.0.rc1.237.g0d66db33f3-goog