[PATCH 7/9] KVM: x86: revalidate steal time cache if MSR value changes

[Rishabh Bhatnagar <risbhat@amazon.com>]

From: Paolo Bonzini <pbonzini@redhat.com>

commit 901d3765fa804ce42812f1d5b1f3de2dfbb26723 upstream.

Commit 7e2175ebd695 ("KVM: x86: Fix recording of guest steal time
/ preempted status", 2021-11-11) open coded the previous call to
kvm_map_gfn, but in doing so it dropped the comparison between the cached
guest physical address and the one in the MSR.  This cause an incorrect
cache hit if the guest modifies the steal time address while the memslots
remain the same.  This can happen with kexec, in which case the steal
time data is written at the address used by the old kernel instead of
the old one.

While at it, rename the variable from gfn to gpa since it is a plain
physical address and not a right-shifted one.

Reported-by: Dave Young <ruyang@redhat.com>
Reported-by: Xiaoying Yan  <yiyan@redhat.com>
Analyzed-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
Cc: David Woodhouse <dwmw@amazon.co.uk>
Cc: stable@vger.kernel.org
Fixes: 7e2175ebd695 ("KVM: x86: Fix recording of guest steal time / preempted status")
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Rishabh Bhatnagar <risbhat@amazon.com>
Tested-by: Allen Pais <apais@linux.microsoft.com>
Acked-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/x86.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 116a225fb26e..0503bb8b64e5 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3025,6 +3025,7 @@ static void record_steal_time(struct kvm_vcpu *vcpu)
 	struct gfn_to_hva_cache *ghc = &vcpu->arch.st.cache;
 	struct kvm_steal_time __user *st;
 	struct kvm_memslots *slots;
+	gpa_t gpa = vcpu->arch.st.msr_val & KVM_STEAL_VALID_BITS;
 	u64 steal;
 	u32 version;
 
@@ -3037,13 +3038,12 @@ static void record_steal_time(struct kvm_vcpu *vcpu)
 	slots = kvm_memslots(vcpu->kvm);
 
 	if (unlikely(slots->generation != ghc->generation ||
+		     gpa != ghc->gpa ||
 		     kvm_is_error_hva(ghc->hva) || !ghc->memslot)) {
-		gfn_t gfn = vcpu->arch.st.msr_val & KVM_STEAL_VALID_BITS;
-
 		/* We rely on the fact that it fits in a single page. */
 		BUILD_BUG_ON((sizeof(*st) - 1) & KVM_STEAL_VALID_BITS);
 
-		if (kvm_gfn_to_hva_cache_init(vcpu->kvm, ghc, gfn, sizeof(*st)) ||
+		if (kvm_gfn_to_hva_cache_init(vcpu->kvm, ghc, gpa, sizeof(*st)) ||
 		    kvm_is_error_hva(ghc->hva) || !ghc->memslot)
 			return;
 	}
-- 
2.39.2