Re: [PATCH 9/8] KVM: x86: limit MSR_IA32_SPEC_CTRL access based on CPUID availability

[Eric Wheeler]

On Tue, 9 Jan 2018, Paolo Bonzini wrote:
> MSR_IA32_SPEC_CTRL is not available unless CPU[7,0].EDX[26] is 1.
> Check that against host CPUID or guest CPUID, respectively for
> host-initiated and guest-initiated accesses.

Hi Radim, Paolo:

In porting this patch series to v4.14, I'm getting this BUILD_BUG_ON:

In file included from arch/x86/kvm/vmx.c:21:0:
In function 'x86_feature_cpuid',
    inlined from 'guest_cpuid_get_register' at arch/x86/kvm/cpuid.h:72:25,
    inlined from 'vmx_get_msr' at arch/x86/kvm/cpuid.h:101:6:
arch/x86/kvm/cpuid.h:64:232: error: call to '__compiletime_assert_64' 
declared with attribute error: BUILD_BUG_ON failed: 
reverse_cpuid[x86_leaf].function == 0
  BUILD_BUG_ON(reverse_cpuid[x86_leaf].function == 0);
                                                                                                                                                                                                                                        
^
In function 'x86_feature_cpuid',
    inlined from 'guest_cpuid_get_register' at arch/x86/kvm/cpuid.h:72:25,
    inlined from 'vmx_set_msr' at arch/x86/kvm/cpuid.h:101:6:
arch/x86/kvm/cpuid.h:64:232: error: call to '__compiletime_assert_64' 
declared with attribute error: BUILD_BUG_ON failed: 
reverse_cpuid[x86_leaf].function == 0
  BUILD_BUG_ON(reverse_cpuid[x86_leaf].function == 0);
                                                                                                                                                                                                                                        

I think this is caused by the following call stack for 
X86_FEATURE_SPEC_CTRL, but if not please correct me here:

arch/x86/kvm/vmx.c:
vmx_get_msr/vmx_set_msr()
	guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL)
		guest_cpuid_get_register(vcpu, x86_feature); 
			x86_feature_cpuid(x86_feature);
				x86_feature_cpuid(unsigned x86_feature)
					BUILD_BUG_ON(reverse_cpuid[x86_leaf].function == 0);


It looks like I need to add something to reverse_cpuid[] but I'm not sure 
what.  

Do you know what needs to be added here?

-Eric

--
Eric Wheeler



> 
> Suggested-by: Jim Mattson <jmattson@xxxxxxxxxx>
> Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
> ---
> 	This is for after X86_FEATURE_SPEC_CTRL is added to Linux, but
> 	I still wanted to ack Jim's improvement.
> 
>  arch/x86/kvm/svm.c | 8 ++++++++
>  arch/x86/kvm/vmx.c | 8 ++++++++
>  2 files changed, 16 insertions(+)
> 
> diff --git a/arch/x86/kvm/svm.c b/arch/x86/kvm/svm.c
> index 97126c2bd663..3a646580d7c5 100644
> --- a/arch/x86/kvm/svm.c
> +++ b/arch/x86/kvm/svm.c
> @@ -3648,6 +3648,10 @@ static int svm_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>  		msr_info->data = svm->nested.vm_cr_msr;
>  		break;
>  	case MSR_IA32_SPEC_CTRL:
> +		if (!static_cpu_has(X86_FEATURE_SPEC_CTRL) ||
> +	    	    (!msr_info->host_initiated &&
> +       		     !guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL)))
> +			return 1;
>  		msr_info->data = svm->spec_ctrl;
>  		break;
>  	case MSR_IA32_UCODE_REV:
> @@ -3806,6 +3810,10 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
>  		vcpu_unimpl(vcpu, "unimplemented wrmsr: 0x%x data 0x%llx\n", ecx, data);
>  		break;
>  	case MSR_IA32_SPEC_CTRL:
> +		if (!static_cpu_has(X86_FEATURE_SPEC_CTRL) ||
> +	    	    (!msr_info->host_initiated &&
> +       		     !guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL)))
> +			return 1;
>  		svm->spec_ctrl = data;
>  		break;
>  	case MSR_IA32_APICBASE:
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 49b4a2d61603..42bc7ee293e4 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -3368,6 +3368,10 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>  		msr_info->data = guest_read_tsc(vcpu);
>  		break;
>  	case MSR_IA32_SPEC_CTRL:
> +		if (!static_cpu_has(X86_FEATURE_SPEC_CTRL) ||
> +		    (!msr_info->host_initiated &&
> +		     !guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL)))
> +			return 1;
>  		msr_info->data = to_vmx(vcpu)->spec_ctrl;
>  		break;
>  	case MSR_IA32_SYSENTER_CS:
> @@ -3510,6 +3514,10 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>  		kvm_write_tsc(vcpu, msr_info);
>  		break;
>  	case MSR_IA32_SPEC_CTRL:
> +		if (!static_cpu_has(X86_FEATURE_SPEC_CTRL) ||
> +		    (!msr_info->host_initiated &&
> +		     !guest_cpuid_has(vcpu, X86_FEATURE_SPEC_CTRL)))
> +			return 1;
>  		to_vmx(vcpu)->spec_ctrl = data;
>  		break;
>  	case MSR_IA32_CR_PAT:
> -- 
> 1.8.3.1
> 
>