[PATCH 5.15 002/145] KVM: x86/mmu: fix NULL pointer dereference on guest INVPCID

[Greg Kroah-Hartman]

From: Paolo Bonzini <pbonzini@xxxxxxxxxx>

commit 9f46c187e2e680ecd9de7983e4d081c3391acc76 upstream.

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@xxxxxxxxxx>
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
[fix conflict due to missing b9e5603c2a3accbadfec570ac501a54431a6bdba]
Signed-off-by: Vegard Nossum <vegard.nossum@xxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
---
 arch/x86/kvm/mmu/mmu.c |    6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/arch/x86/kvm/mmu/mmu.c
+++ b/arch/x86/kvm/mmu/mmu.c
@@ -5396,14 +5396,16 @@ void kvm_mmu_invpcid_gva(struct kvm_vcpu
 	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;
 		}
 	}