WARN if KVM is about to derference a NULL pae_root when loading an MMU,
and convert the BUG() on a bad shadow_root_level into a WARN (now that
errors are handled cleanly). With nested NPT, botching the level and
sending KVM down the wrong path is all too easy, and the on-demand
allocation of pae_root means bugs crash the host. Obviously, KVM could
unconditionally allocate pae_root, but that's arguably a worse failure
mode as it would potentially corrupt the guest instead of crashing it.
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
arch/x86/kvm/mmu/mmu.c | 11 +++++++++--
1 file changed, 9 insertions(+), 2 deletions(-)
diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 34eeb39ee0f9..35f89bb1f205 100644
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -3247,6 +3247,9 @@ static int mmu_alloc_direct_roots(struct kvm_vcpu *vcpu)
true);
vcpu->arch.mmu->root_hpa = root;
} else if (shadow_root_level == PT32E_ROOT_LEVEL) {
+ if (WARN_ON_ONCE(!vcpu->arch.mmu->pae_root))
+ return -EIO;
+
for (i = 0; i < 4; ++i) {
WARN_ON_ONCE(vcpu->arch.mmu->pae_root[i]);
@@ -3256,8 +3259,10 @@ static int mmu_alloc_direct_roots(struct kvm_vcpu *vcpu)
shadow_me_mask;
}
vcpu->arch.mmu->root_hpa = __pa(vcpu->arch.mmu->pae_root);
- } else
- BUG();
+ } else {
+ WARN_ONCE(1, "Bad TDP root level = %d\n", shadow_root_level);
+ return -EIO;
+ }
/* root_pgd is ignored for direct MMUs. */
vcpu->arch.mmu->root_pgd = 0;
@@ -3340,6 +3345,8 @@ static int mmu_alloc_shadow_roots(struct kvm_vcpu *vcpu)
vcpu->arch.mmu->lm_root = lm_root;
lm_root[0] = __pa(vcpu->arch.mmu->pae_root) | pm_mask;
+ } else if (WARN_ON_ONCE(!vcpu->arch.mmu->pae_root)) {
+ return -EIO;
}
for (i = 0; i < 4; ++i) {
--
2.30.1.766.gb4fecdf3b7-goog
