x86: KVM: SVM: always update the x2avic msr interception

commit b65235f6e102354ccafda601eaa1c5bef5284d21 upstream.

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@vger.kernel.org
Signed-off-by: Maxim Levitsky <mlevitsk@redhat.com>
Reviewed-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Tested-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Reviewed-by: Sean Christopherson <seanjc@google.com>
Message-Id: <20230928173354.217464-2-mlevitsk@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: SeongJae Park <sj@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index c871a6d6364ca4710bcf4da43ee32b1dad8c3bc1..4194aa4c5f0e0c531fa79c0db3f12df4fd459439 100644 (file)
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -822,8 +822,7 @@ void svm_set_x2apic_msr_interception(struct vcpu_svm *svm, bool intercept)
        if (intercept == svm->x2avic_msrs_intercepted)
                return;
 
-       if (avic_mode != AVIC_MODE_X2 ||
-           !apic_x2apic_mode(svm->vcpu.arch.apic))
+       if (avic_mode != AVIC_MODE_X2)
                return;
 
        for (i = 0; i < MAX_DIRECT_ACCESS_MSRS; i++) {