KVM: x86: Signal #GP, not -EPERM, on bad WRMSR(MCi_CTL/STATUS)

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@vger.kernel.org
Signed-off-by: Sean Christopherson <seanjc@google.com>
Reviewed-by: Jim Mattson <jmattson@google.com>
Link: https://lore.kernel.org/r/20220512222716.4112548-2-seanjc@google.com

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 7ce0c6f..891ca97 100644 (file)
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -3239,13 +3239,13 @@ static int set_msr_mce(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
                         */
                        if ((offset & 0x3) == 0 &&
                            data != 0 && (data | (1 << 10) | 1) != ~(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;