[PATCH 5.18 0040/1095] KVM: x86: do not report preemption if the steal time cache is stale

Greg Kroah-Hartman
2022-08-15T20:16:51Z

From: Paolo Bonzini <pbonzini@redhat.com>

commit c3c28d24d910a746b02f496d190e0e8c6560224b 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 preempted
bit is written at the address used by the old kernel instead of
the old one.

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: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
arch/x86/kvm/x86.c | 2 ++
1 file changed, 2 insertions(+)

--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -4614,6 +4614,7 @@ static void kvm_steal_time_set_preempted
struct kvm_steal_time __user *st;
struct kvm_memslots *slots;
static const u8 preempted = KVM_VCPU_PREEMPTED;
+ gpa_t gpa = vcpu->arch.st.msr_val & KVM_STEAL_VALID_BITS;

/*
* The vCPU can be marked preempted if and only if the VM-Exit was on
@@ -4641,6 +4642,7 @@ static void kvm_steal_time_set_preempted
slots = kvm_memslots(vcpu->kvm);

if (unlikely(slots->generation != ghc->generation ||
+ gpa != ghc->gpa ||
kvm_is_error_hva(ghc->hva) || !ghc->memslot))
return;