[SRU][F][PATCH 1/1] KVM: x86/mmu: fix NULL pointer dereference on guest INVPCID

[Cengiz Can]

From: Paolo Bonzini <pbonzini at redhat.com>

CVE-2022-1789

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 at zju.edu.cn>
Cc: stable at vger.kernel.org
Signed-off-by: Paolo Bonzini <pbonzini at redhat.com>
(backported from commit 9f46c187e2e680ecd9de7983e4d081c3391acc76)
[cengizcan: use mmu->root_hpa instead of non-existing mmu->root.hpa]
[cengizcan: adapted for 5.4 due to path and context differences]
Signed-off-by: Cengiz Can <cengiz.can at canonical.com>
---
 arch/x86/kvm/mmu.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/mmu.c b/arch/x86/kvm/mmu.c
index d3877dd713ae..fd1748ea4e44 100644
--- a/arch/x86/kvm/mmu.c
+++ b/arch/x86/kvm/mmu.c
@@ -5636,14 +5636,16 @@ 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].cr3)) {
-			mmu->invlpg(vcpu, gva, mmu->prev_roots[i].hpa);
+			if (mmu->invlpg)
+				mmu->invlpg(vcpu, gva, mmu->prev_roots[i].hpa);
 			tlb_flush = true;
 		}
 	}
-- 
2.34.1