[SRU][Mantic][PATCH 1/1] x86: KVM: SVM: always update the x2avic msr interception

[Yuxuan Luo]

From: Maxim Levitsky <mlevitsk at redhat.com>

The following problem exists since x2avic was enabled in the KVM:

svm_set_x2apic_msr_interception is called to enable the interception of
the x2apic msrs.

In particular it is called at the moment the guest resets its apic.

Assuming that the guest's apic was in x2apic mode, the reset will bring
it back to the xapic mode.

The svm_set_x2apic_msr_interception however has an erroneous check for
'!apic_x2apic_mode()' which prevents it from doing anything in this case.

As a result of this, all x2apic msrs are left unintercepted, and that
exposes the bare metal x2apic (if enabled) to the guest.
Oops.

Remove the erroneous '!apic_x2apic_mode()' check to fix that.

This fixes CVE-2023-5090

Fixes: 4d1d7942e36a ("KVM: SVM: Introduce logic to (de)activate x2AVIC mode")
Cc: stable at vger.kernel.org
Signed-off-by: Maxim Levitsky <mlevitsk at redhat.com>
Reviewed-by: Suravee Suthikulpanit <suravee.suthikulpanit at amd.com>
Tested-by: Suravee Suthikulpanit <suravee.suthikulpanit at amd.com>
Reviewed-by: Sean Christopherson <seanjc at google.com>
Message-Id: <20230928173354.217464-2-mlevitsk at redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini at redhat.com>
(cherry picked from commit b65235f6e102354ccafda601eaa1c5bef5284d21)
CVE-2023-5090
Signed-off-by: Yuxuan Luo <yuxuan.luo at canonical.com>
---
 arch/x86/kvm/svm/svm.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index d4bfdc607fe7f..2ec76ab525eae 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -819,8 +819,7 @@ void svm_set_x2apic_msr_interception(struct vcpu_svm *svm, bool intercept)
 	if (intercept == svm->x2avic_msrs_intercepted)
 		return;
 
-	if (!x2avic_enabled ||
-	    !apic_x2apic_mode(svm->vcpu.arch.apic))
+	if (!x2avic_enabled)
 		return;
 
 	for (i = 0; i < MAX_DIRECT_ACCESS_MSRS; i++) {
-- 
2.34.1