KVM: x86: Inject #GP on x2APIC WRMSR that sets reserved bits 63:32

Reject attempts to set bits 63:32 for 32-bit x2APIC registers, i.e. all
x2APIC registers except ICR.  Per Intel's SDM:

  Non-zero writes (by WRMSR instruction) to reserved bits to these
  registers will raise a general protection fault exception

Opportunistically fix a typo in a nearby comment.

Reported-by: Marc Orr <[email protected]>
Cc: [email protected]
Reviewed-by: Maxim Levitsky <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Sean Christopherson <[email protected]>

1 files changed, 5 insertions, 1 deletions

diff --git a/arch/x86/kvm/lapic.c b/arch/x86/kvm/lapic.c
index 9aca006b2d22..814b65106057 100644
--- a/arch/x86/kvm/lapic.c
+++ b/arch/x86/kvm/lapic.c
@@ -3114,13 +3114,17 @@ static int kvm_lapic_msr_read(struct kvm_lapic *apic, u32 reg, u64 *data)
 static int kvm_lapic_msr_write(struct kvm_lapic *apic, u32 reg, u64 data)
 {
 	/*
-	 * ICR is a 64-bit register in x2APIC mode (and Hyper'v PV vAPIC) and
+	 * ICR is a 64-bit register in x2APIC mode (and Hyper-V PV vAPIC) and
 	 * can be written as such, all other registers remain accessible only
 	 * through 32-bit reads/writes.
 	 */
 	if (reg == APIC_ICR)
 		return kvm_x2apic_icr_write(apic, data);
 
+	/* Bits 63:32 are reserved in all other registers. */
+	if (data >> 32)
+		return 1;
+
 	return kvm_lapic_reg_write(apic, reg, (u32)data);
 }