[PATCH] KVM: X86: #GP when guest attempts to write MCi banks w/o 0

[Wanpeng Li <kernellwp@gmail.com>]

From: Wanpeng Li <wanpeng.li@hotmail.com>

SDM section 15.3.2.2~15.3.2.4 mentioned that MCi_STATUS/ADDR/MISC, when the 
registers are implemented, these registers can be cleared by explicitly writing 
0s to these registers. Writing 1s to these registers will cause a 
general-protection exception.

The mce is emulated in qemu, so just the guest attempts to write 1 to these 
registers should cause a #GP, this patch does it.

Cc: Radim Krčmář <rkrcmar@redhat.com>
Cc: Jim Mattson <jmattson@google.com>
Signed-off-by: Wanpeng Li <wanpeng.li@hotmail.com>
---
 arch/x86/kvm/x86.c | 9 +++++++--
 1 file changed, 7 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 5669af0..a8680ea 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -2006,10 +2006,12 @@ static void kvmclock_sync_fn(struct work_struct *work)
 					KVMCLOCK_SYNC_PERIOD);
 }
 
-static int set_msr_mce(struct kvm_vcpu *vcpu, u32 msr, u64 data)
+static int set_msr_mce(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 {
 	u64 mcg_cap = vcpu->arch.mcg_cap;
 	unsigned bank_num = mcg_cap & 0xff;
+	u32 msr = msr_info->index;
+	u64 data = msr_info->data;
 
 	switch (msr) {
 	case MSR_IA32_MCG_STATUS:
@@ -2034,6 +2036,9 @@ static int set_msr_mce(struct kvm_vcpu *vcpu, u32 msr, u64 data)
 			if ((offset & 0x3) == 0 &&
 			    data != 0 && (data | (1 << 10)) != ~(u64)0)
 				return -1;
+			if (!msr_info->host_initiated &&
+				(offset & 0x3) != 0 && data != 0)
+				return -1;
 			vcpu->arch.mce_banks[offset] = data;
 			break;
 		}
@@ -2283,7 +2288,7 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 	case MSR_IA32_MCG_CTL:
 	case MSR_IA32_MCG_STATUS:
 	case MSR_IA32_MC0_CTL ... MSR_IA32_MCx_CTL(KVM_MAX_MCE_BANKS) - 1:
-		return set_msr_mce(vcpu, msr, data);
+		return set_msr_mce(vcpu, msr_info);
 
 	case MSR_K7_PERFCTR0 ... MSR_K7_PERFCTR3:
 	case MSR_P6_PERFCTR0 ... MSR_P6_PERFCTR1:
-- 
2.7.4