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Subject: Re: [PATCH 2/4] kvm: vmx: Raise #UD on unsupported RDRAND
To: Paolo Bonzini <pbonzini@redhat.com>, linux-kernel@vger.kernel.org,
        kvm@vger.kernel.org
Cc: jmattson@google.com
References: <1503581879-52125-1-git-send-email-pbonzini@redhat.com>
 <1503581879-52125-3-git-send-email-pbonzini@redhat.com>
From: David Hildenbrand <david@redhat.com>
Organization: Red Hat GmbH
Message-ID: <f992b8d2-ccbb-7958-49a6-77eaeff7ffa7@redhat.com>
Date: Thu, 24 Aug 2017 19:42:30 +0200
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On 24.08.2017 15:37, Paolo Bonzini wrote:
> From: Jim Mattson <jmattson@google.com>
> 
> A guest may not be configured to support RDRAND, even when the host
> does. If the guest does not support RDRAND, intercept the instruction
> and synthesize #UD. Also clear the "allowed-1" bit for RDRAND exiting
> in the IA32_VMX_PROCBASED_CTLS2 MSR.
> 
> Signed-off-by: Jim Mattson <jmattson@google.com>
> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
> ---
>  arch/x86/kvm/vmx.c | 31 ++++++++++++++++++++++++++++++-
>  1 file changed, 30 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/x86/kvm/vmx.c b/arch/x86/kvm/vmx.c
> index 08381a5d8879..1f2c69de7872 100644
> --- a/arch/x86/kvm/vmx.c
> +++ b/arch/x86/kvm/vmx.c
> @@ -2818,7 +2818,7 @@ static void nested_vmx_setup_ctls_msrs(struct vcpu_vmx *vmx)
>  		vmx->nested.nested_vmx_secondary_ctls_high);
>  	vmx->nested.nested_vmx_secondary_ctls_low = 0;
>  	vmx->nested.nested_vmx_secondary_ctls_high &=
> -		SECONDARY_EXEC_RDRAND | SECONDARY_EXEC_RDSEED |
> +		SECONDARY_EXEC_RDSEED |
>  		SECONDARY_EXEC_VIRTUALIZE_APIC_ACCESSES |
>  		SECONDARY_EXEC_DESC |
>  		SECONDARY_EXEC_VIRTUALIZE_X2APIC_MODE |
> @@ -3671,6 +3671,7 @@ static __init int setup_vmcs_config(struct vmcs_config *vmcs_conf)
>  			SECONDARY_EXEC_VIRTUAL_INTR_DELIVERY |
>  			SECONDARY_EXEC_SHADOW_VMCS |
>  			SECONDARY_EXEC_XSAVES |
> +			SECONDARY_EXEC_RDRAND |
>  			SECONDARY_EXEC_ENABLE_PML |
>  			SECONDARY_EXEC_TSC_SCALING |
>  			SECONDARY_EXEC_ENABLE_VMFUNC;
> @@ -5273,6 +5274,12 @@ static u32 vmx_exec_control(struct vcpu_vmx *vmx)
>  	return exec_control;
>  }
>  
> +static bool vmx_rdrand_supported(void)
> +{
> +	return vmcs_config.cpu_based_2nd_exec_ctrl &
> +		SECONDARY_EXEC_RDRAND;
> +}
> +
>  static void vmx_compute_secondary_exec_control(struct vcpu_vmx *vmx)
>  {
>  	struct kvm_vcpu *vcpu = &vmx->vcpu;
> @@ -5342,6 +5349,21 @@ static void vmx_compute_secondary_exec_control(struct vcpu_vmx *vmx)
>  		}
>  	}
>  
> +	if (vmx_rdrand_supported()) {
> +		bool rdrand_enabled = guest_cpuid_has(vcpu, X86_FEATURE_RDRAND);
> +		if (rdrand_enabled)
> +			exec_control &= ~SECONDARY_EXEC_RDRAND;
> +
> +		if (nested) {
> +			if (rdrand_enabled)
> +				vmx->nested.nested_vmx_secondary_ctls_high |=
> +					SECONDARY_EXEC_RDRAND;
> +			else
> +				vmx->nested.nested_vmx_secondary_ctls_high &=
> +					~SECONDARY_EXEC_RDRAND;
> +		}
> +	}
> +
>  	vmx->secondary_exec_control = exec_control;
>  }
>  
> @@ -6847,6 +6869,12 @@ static int handle_mwait(struct kvm_vcpu *vcpu)
>  	return handle_nop(vcpu);
>  }
>  
> +static int handle_invalid_op(struct kvm_vcpu *vcpu)
> +{
> +	kvm_queue_exception(vcpu, UD_VECTOR);
> +	return 1;
> +}
> +
>  static int handle_monitor_trap(struct kvm_vcpu *vcpu)
>  {
>  	return 1;
> @@ -8090,6 +8118,7 @@ static int (*const kvm_vmx_exit_handlers[])(struct kvm_vcpu *vcpu) = {
>  	[EXIT_REASON_MONITOR_INSTRUCTION]     = handle_monitor,
>  	[EXIT_REASON_INVEPT]                  = handle_invept,
>  	[EXIT_REASON_INVVPID]                 = handle_invvpid,
> +	[EXIT_REASON_RDRAND]                  = handle_invalid_op,
>  	[EXIT_REASON_XSAVES]                  = handle_xsaves,
>  	[EXIT_REASON_XRSTORS]                 = handle_xrstors,
>  	[EXIT_REASON_PML_FULL]		      = handle_pml_full,
> 

Reviewed-by: David Hildenbrand <david@redhat.com>

-- 

Thanks,

David