[PATCH v3 2/3] KVM: VMX: validate individual bits of guest MSR_IA32_FEATURE_CONTROL

[Haozhong Zhang]

KVM currently does not check the value written to guest
MSR_IA32_FEATURE_CONTROL, though bits corresponding to disabled features
may be set. This patch makes KVM to validate individual bits written to
guest MSR_IA32_FEATURE_CONTROL according to enabled features.

Signed-off-by: Haozhong Zhang <haozhong.zhang@xxxxxxxxx>
---
 arch/x86/kvm/vmx.c | 25 ++++++++++++++++++++++++-
 1 file changed, 24 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index ad66978..0a3ccb0 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -612,7 +612,13 @@ struct vcpu_vmx {
 	u32 guest_pkru;
 	u32 host_pkru;
 
+	/*
+	 * Only bits masked by msr_ia32_feature_control_valid_bits can be set in
+	 * msr_ia32_feature_control. FEATURE_CONTROL_LOCKED is always included
+	 * in msr_ia32_feature_control_valid_bits.
+	 */
 	u64 msr_ia32_feature_control;
+	u64 msr_ia32_feature_control_valid_bits;
 };
 
 enum segment_cache_field {
@@ -2929,6 +2935,14 @@ static int vmx_get_vmx_msr(struct kvm_vcpu *vcpu, u32 msr_index, u64 *pdata)
 	return 0;
 }
 
+static inline bool vmx_feature_control_msr_valid(struct kvm_vcpu *vcpu,
+						 uint64_t val)
+{
+	uint64_t valid_bits = to_vmx(vcpu)->msr_ia32_feature_control_valid_bits;
+
+	return !(val & ~valid_bits);
+}
+
 /*
  * Reads an msr value (of 'msr_index') into 'pdata'.
  * Returns 0 on success, non-0 otherwise.
@@ -3062,7 +3076,7 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		ret = kvm_set_msr_common(vcpu, msr_info);
 		break;
 	case MSR_IA32_FEATURE_CONTROL:
-		if (!nested_vmx_allowed(vcpu) ||
+		if (!vmx_feature_control_msr_valid(vcpu, data) ||
 		    (to_vmx(vcpu)->msr_ia32_feature_control &
 		     FEATURE_CONTROL_LOCKED && !msr_info->host_initiated))
 			return 1;
@@ -9055,6 +9069,8 @@ static struct kvm_vcpu *vmx_create_vcpu(struct kvm *kvm, unsigned int id)
 			goto free_vmcs;
 	}
 
+	vmx->msr_ia32_feature_control_valid_bits = FEATURE_CONTROL_LOCKED;
+
 	return &vmx->vcpu;
 
 free_vmcs:
@@ -9202,6 +9218,13 @@ static void vmx_cpuid_update(struct kvm_vcpu *vcpu)
 			vmx->nested.nested_vmx_secondary_ctls_high &=
 				~SECONDARY_EXEC_PCOMMIT;
 	}
+
+	if (nested_vmx_allowed(vcpu))
+		to_vmx(vcpu)->msr_ia32_feature_control_valid_bits |=
+			FEATURE_CONTROL_VMXON_ENABLED_OUTSIDE_SMX;
+	else
+		to_vmx(vcpu)->msr_ia32_feature_control_valid_bits &=
+			~FEATURE_CONTROL_VMXON_ENABLED_OUTSIDE_SMX;
 }
 
 static void vmx_set_supported_cpuid(u32 func, struct kvm_cpuid_entry2 *entry)
-- 
2.9.0