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Subject[PATCH v2 2/3] KVM: VMX: validate individual bits of guest MSR_IA32_FEATURE_CONTROL
Date
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@intel.com>
---
arch/x86/kvm/vmx.c | 52 ++++++++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 50 insertions(+), 2 deletions(-)

diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
index 6b63f2d..1dc89c5 100644
--- a/arch/x86/kvm/vmx.c
+++ b/arch/x86/kvm/vmx.c
@@ -602,7 +602,16 @@ 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.
+ *
+ * msr_ia32_feature_control_valid_bits should be modified by
+ * feature_control_valid_bits_add/del(), and only bits masked by
+ * FEATURE_CONTROL_MAX_VALID_BITS can be modified.
+ */
u64 msr_ia32_feature_control;
+ u64 msr_ia32_feature_control_valid_bits;
};

enum segment_cache_field {
@@ -624,6 +633,30 @@ static struct pi_desc *vcpu_to_pi_desc(struct kvm_vcpu *vcpu)
return &(to_vmx(vcpu)->pi_desc);
}

+/*
+ * FEATURE_CONTROL_LOCKED is added/removed automatically by
+ * feature_control_valid_bits_add/del(), so it's not included here.
+ */
+#define FEATURE_CONTROL_MAX_VALID_BITS \
+ FEATURE_CONTROL_VMXON_ENABLED_OUTSIDE_SMX
+
+static void feature_control_valid_bits_add(struct kvm_vcpu *vcpu, uint64_t bits)
+{
+ ASSERT(!(bits & ~FEATURE_CONTROL_MAX_VALID_BITS));
+ to_vmx(vcpu)->msr_ia32_feature_control_valid_bits |=
+ bits | FEATURE_CONTROL_LOCKED;
+}
+
+static void feature_control_valid_bits_del(struct kvm_vcpu *vcpu, uint64_t bits)
+{
+ uint64_t *valid_bits =
+ &to_vmx(vcpu)->msr_ia32_feature_control_valid_bits;
+ ASSERT(!(bits & ~FEATURE_CONTROL_MAX_VALID_BITS));
+ *valid_bits &= ~bits;
+ if (!(*valid_bits & ~FEATURE_CONTROL_LOCKED))
+ *valid_bits = 0;
+}
+
#define VMCS12_OFFSET(x) offsetof(struct vmcs12, x)
#define FIELD(number, name) [number] = VMCS12_OFFSET(name)
#define FIELD64(number, name) [number] = VMCS12_OFFSET(name), \
@@ -2864,6 +2897,14 @@ 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 valid_bits && !(val & ~valid_bits);
+}
+
/*
* Reads an msr value (of 'msr_index') into 'pdata'.
* Returns 0 on success, non-0 otherwise.
@@ -2906,7 +2947,7 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
msr_info->data = vmcs_read64(GUEST_BNDCFGS);
break;
case MSR_IA32_FEATURE_CONTROL:
- if (!nested_vmx_allowed(vcpu))
+ if (!vmx_feature_control_msr_valid(vcpu, 0))
return 1;
msr_info->data = to_vmx(vcpu)->msr_ia32_feature_control;
break;
@@ -2999,7 +3040,7 @@ 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;
@@ -9095,6 +9136,13 @@ static void vmx_cpuid_update(struct kvm_vcpu *vcpu)
vmx->nested.nested_vmx_secondary_ctls_high &=
~SECONDARY_EXEC_PCOMMIT;
}
+
+ if (nested_vmx_allowed(vcpu))
+ feature_control_valid_bits_add
+ (vcpu, FEATURE_CONTROL_VMXON_ENABLED_OUTSIDE_SMX);
+ else
+ feature_control_valid_bits_del
+ (vcpu, FEATURE_CONTROL_VMXON_ENABLED_OUTSIDE_SMX);
}

static void vmx_set_supported_cpuid(u32 func, struct kvm_cpuid_entry2 *entry)
--
2.9.0
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