Re: [PATCH v2 2/3] KVM: VMX: validate individual bits of guest MSR_IA32_FEATURE_CONTROL

Paolo Bonzini
2016-06-16T10:01:13Z

On 16/06/2016 08:05, Haozhong Zhang wrote:
> +/*
> + * 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));

The KVM-specific ASSERT macro should go. You can use WARN_ON.

However, I think FEATURE_CONTROL_LOCKED should always be writable. If
you change that, it's simpler to just do |= and &= in the caller.

> + 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))

You can remove this if completely in patch 1. It's okay to make the MSR
always available.

Thanks,

Paolo

> 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);
> }