KVM: x86: Inject #GP if WRMSR sets reserved bits in APIC Self-IPI

Inject a #GP if the guest attempts to set reserved bits in the x2APIC-only
Self-IPI register.  Bits 7:0 hold the vector, all other bits are reserved.

Reported-by: Marc Orr <marcorr@google.com>
Cc: Ben Gardon <bgardon@google.com>
Cc: Venkatesh Srinivas <venkateshs@chromium.org>
Cc: stable@vger.kernel.org
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Link: https://lore.kernel.org/r/20230107011025.565472-2-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 08450b3e7040c323ce9359d09468cc735f81ea13..9aca006b2d225e891bf00f57cf23a13f3b27edf1 100644 (file)
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -2324,10 +2324,14 @@ static int kvm_lapic_reg_write(struct kvm_lapic *apic, u32 reg, u32 val)
                break;
 
        case APIC_SELF_IPI:
-               if (apic_x2apic_mode(apic))
-                       kvm_apic_send_ipi(apic, APIC_DEST_SELF | (val & APIC_VECTOR_MASK), 0);
-               else
+               /*
+                * Self-IPI exists only when x2APIC is enabled.  Bits 7:0 hold
+                * the vector, everything else is reserved.
+                */
+               if (!apic_x2apic_mode(apic) || (val & ~APIC_VECTOR_MASK))
                        ret = 1;
+               else
+                       kvm_apic_send_ipi(apic, APIC_DEST_SELF | val, 0);
                break;
        default:
                ret = 1;