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

From: Haozhong Zhang
Date: Wed Jun 22 2016 - 03:01:06 EST


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