[PATCH 1/3] KVM: x86: Signal #GP, not -EPERM, on bad WRMSR(MCi_CTL/STATUS)

[Sean Christopherson]

Return '1', not '-1', when handling an illegal WRMSR to a MCi_CTL or
MCi_STATUS MSR.  The behavior of "all zeros' or "all ones" for CTL MSRs
is architectural, as is the "only zeros" behavior for STATUS MSRs.  I.e.
the intent is to inject a #GP, not exit to userspace due to an unhandled
emulation case.  Returning '-1' gets interpreted as -EPERM up the stack
and effecitvely kills the guest.

Fixes: 890ca9aefa78 ("KVM: Add MCE support")
Fixes: 9ffd986c6e4e ("KVM: X86: #GP when guest attempts to write MCi_STATUS register w/o 0")
Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Sean Christopherson <seanjc@xxxxxxxxxx>
---
 arch/x86/kvm/x86.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 8ee8c91fa762..bc6db58975dc 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3233,13 +3233,13 @@ static int set_msr_mce(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 			 */
 			if ((offset & 0x3) == 0 &&
 			    data != 0 && (data | (1 << 10)) != ~(u64)0)
-				return -1;
+				return 1;
 
 			/* MCi_STATUS */
 			if (!msr_info->host_initiated &&
 			    (offset & 0x3) == 1 && data != 0) {
 				if (!can_set_mci_status(vcpu))
-					return -1;
+					return 1;
 			}
 
 			vcpu->arch.mce_banks[offset] = data;
-- 
2.36.0.550.gb090851708-goog