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

[Paolo Bonzini]

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);
>  }