[PATCH 1/6] KVM: x86: Inject #GP if WRMSR sets reserved bits in APIC Self-IPI

[Sean Christopherson <seanjc@google.com>]

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
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
 arch/x86/kvm/lapic.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 80f92cbc4029..f77da92c6ea6 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -2315,10 +2315,14 @@ 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;
-- 
2.39.0.314.g84b9a713c41-goog