linux-kernel - [PATCH 9/8] KVM: x86: limit MSR_IA32_SPEC_CTRL access based on CPUID availability

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Date:   Tue,  9 Jan 2018 13:03:11 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     linux-kernel@...r.kernel.org, kvm@...r.kernel.org
Cc:     rkrcmar@...hat.com, liran.alon@...cle.com, jmattson@...gle.com,
        aliguori@...zon.com, thomas.lendacky@....com, dwmw@...zon.co.uk,
        bp@...en8.de, x86@...nel.org
Subject: [PATCH 9/8] KVM: x86: limit MSR_IA32_SPEC_CTRL access based on CPUID availability

MSR_IA32_SPEC_CTRL is not available unless CPU[7,0].EDX[26] is 1.
Check that against host CPUID or guest CPUID, respectively for
host-initiated and guest-initiated accesses.

Suggested-by: Jim Mattson <jmattson@...gle.com>
Signed-off-by: Paolo Bonzini <pbonzini@...hat.com>
---
	This is for after X86_FEATURE_SPEC_CTRL is added to Linux, but
	I still wanted to ack Jim's improvement.

 arch/x86/kvm/svm.c | 8 ++++++++
 arch/x86/kvm/vmx.c | 8 ++++++++
 2 files changed, 16 insertions(+)

diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
index 97126c2bd663..3a646580d7c5 100644
--- a/arch/x86/kvm/svm.c
+++ b/arch/x86/kvm/svm.c
@@ -3648,6 +3648,10 @@ static int svm_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		msr_info->data = svm->nested.vm_cr_msr;
 		break;
 	case MSR_IA32_SPEC_CTRL:
+		if (!static_cpu_has(X86_FEATURE_SPEC_CTRL) ||
+	    	    (!msr_info->host_initiated &&
+       		     !guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL)))
+			return 1;
 		msr_info->data = svm->spec_ctrl;
 		break;
 	case MSR_IA32_UCODE_REV:
@@ -3806,6 +3810,10 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
 		vcpu_unimpl(vcpu, "unimplemented wrmsr: 0x%x data 0x%llx\n", ecx, data);
 		break;
 	case MSR_IA32_SPEC_CTRL:
+		if (!static_cpu_has(X86_FEATURE_SPEC_CTRL) ||
+	    	    (!msr_info->host_initiated &&
+       		     !guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL)))
+			return 1;
 		svm->spec_ctrl = data;
 		break;
 	case MSR_IA32_APICBASE:
diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 49b4a2d61603..42bc7ee293e4 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -3368,6 +3368,10 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		msr_info->data = guest_read_tsc(vcpu);
 		break;
 	case MSR_IA32_SPEC_CTRL:
+		if (!static_cpu_has(X86_FEATURE_SPEC_CTRL) ||
+		    (!msr_info->host_initiated &&
+		     !guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL)))
+			return 1;
 		msr_info->data = to_vmx(vcpu)->spec_ctrl;
 		break;
 	case MSR_IA32_SYSENTER_CS:
@@ -3510,6 +3514,10 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		kvm_write_tsc(vcpu, msr_info);
 		break;
 	case MSR_IA32_SPEC_CTRL:
+		if (!static_cpu_has(X86_FEATURE_SPEC_CTRL) ||
+		    (!msr_info->host_initiated &&
+		     !guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL)))
+			return 1;
 		to_vmx(vcpu)->spec_ctrl = data;
 		break;
 	case MSR_IA32_CR_PAT:
-- 
1.8.3.1