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

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>

diff --git a/arch/x86/kvm/mmu/mmu.c b/arch/x86/kvm/mmu/mmu.c
index 56ebc4f..45e1573 100644 (file)
--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -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;
                }
        }