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KVM: x86/mmu: fix NULL pointer dereference on guest INVPCID

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With shadow paging enabled, the INVPCID instruction results in a call
to kvm_mmu_invpcid_gva.  If INVPCID is executed with CR0.PG=0, the
invlpg callback is not set and the result is a NULL pointer dereference.
Fix it trivially by checking for mmu->invlpg before every call.

There are other possibilities:

- check for CR0.PG, because KVM (like all Intel processors after P5)
  flushes guest TLB on CR0.PG changes so that INVPCID/INVLPG are a
  nop with paging disabled

- check for EFER.LMA, because KVM syncs and flushes when switching
  MMU contexts outside of 64-bit mode

All of these are tricky, go for the simple solution.  This is CVE-2022-1789.

Reported-by: Yongkang Jia <kangel@zju.edu.cn>
Cc: stable@vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This commit is contained in:
Paolo Bonzini 2022-05-20 13:48:11 -04:00
parent ea8c66fe8d
commit 9f46c187e2
1 changed files with 4 additions and 2 deletions
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6
arch/x86/kvm/mmu/mmu.c
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@ -5470,14 +5470,16 @@ void kvm_mmu_invpcid_gva(struct kvm_vcpu *vcpu, gva_t gva, unsigned long pcid)
uint i;
if (pcid == kvm_get_active_pcid(vcpu)) {
mmu->invlpg(vcpu, gva, mmu->root.hpa);
if (mmu->invlpg)
mmu->invlpg(vcpu, gva, mmu->root.hpa);
tlb_flush = true;
}
for (i = 0; i < KVM_MMU_NUM_PREV_ROOTS; i++) {
if (VALID_PAGE(mmu->prev_roots[i].hpa) &&
pcid == kvm_get_pcid(vcpu, mmu->prev_roots[i].pgd)) {
mmu->invlpg(vcpu, gva, mmu->prev_roots[i].hpa);
if (mmu->invlpg)
mmu->invlpg(vcpu, gva, mmu->prev_roots[i].hpa);
tlb_flush = true;
}
}