Re: [PATCH v4] KVM: X86: Allow userspace to define the microcode version

[Tom Lendacky <thomas.lendacky@amd.com>]

On 2/26/2018 8:35 PM, Wanpeng Li wrote:
> From: Wanpeng Li <wanpengli@tencent.com>
> 
> Linux (among the others) has checks to make sure that certain features 
> aren't enabled on a certain family/model/stepping if the microcode version 
> isn't greater than or equal to a known good version.
> 
> By exposing the real microcode version, we're preventing buggy guests that
> don't check that they are running virtualized (i.e., they should trust the
> hypervisor) from disabling features that are effectively not buggy.
> 
> Suggested-by: Filippo Sironi <sironi@amazon.de>
> Cc: Paolo Bonzini <pbonzini@redhat.com>
> Cc: Radim Krčmář <rkrcmar@redhat.com>
> Cc: Liran Alon <liran.alon@oracle.com>
> Cc: Nadav Amit <nadav.amit@gmail.com>
> Signed-off-by: Wanpeng Li <wanpengli@tencent.com>
> ---
> v3 -> v4:
>  * add the shifts back
> v2 -> v3:
>  * remove the shifts
>  * add the MSR_IA32_UCODE_REV version to the "feature MSRs"
> v1 -> v2:
>  * add MSR_IA32_UCODE_REV to emulated_msrs
> 
>  arch/x86/include/asm/kvm_host.h |  1 +
>  arch/x86/kvm/x86.c              | 19 +++++++++++++++----
>  2 files changed, 16 insertions(+), 4 deletions(-)
> 
> diff --git a/arch/x86/include/asm/kvm_host.h b/arch/x86/include/asm/kvm_host.h
> index 938d453..6e13f2f 100644
> --- a/arch/x86/include/asm/kvm_host.h
> +++ b/arch/x86/include/asm/kvm_host.h
> @@ -507,6 +507,7 @@ struct kvm_vcpu_arch {
>  	u64 smi_count;
>  	bool tpr_access_reporting;
>  	u64 ia32_xss;
> +	u32 microcode_version;
>  
>  	/*
>  	 * Paging state of the vcpu
> diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
> index d4985a9..0299b6e 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1058,6 +1058,7 @@ static unsigned num_emulated_msrs;
>  static u32 msr_based_features[] = {
>  	MSR_IA32_ARCH_CAPABILITIES,
>  	MSR_F10H_DECFG,
> +	MSR_IA32_UCODE_REV,
>  };
>  
>  static unsigned int num_msr_based_features;
> @@ -1067,8 +1068,14 @@ static int do_get_msr_feature(struct kvm_vcpu *vcpu, unsigned index, u64 *data)
>  	struct kvm_msr_entry msr;
>  
>  	msr.index = index;
> -	if (kvm_x86_ops->get_msr_feature(&msr))
> -		return 1;
> +	switch (msr.index) {
> +	case MSR_IA32_UCODE_REV:
> +		rdmsrl(msr.index, msr.data);
> +		break;

By not putting this support into the svm/vmx get_msr_feature() functions
this MSR will be removed from the list of msr_based_features (see the
kvm_init_msr_list() function).  You will need to either add this to each
of the get_msr_feature() functions, put similar code to this into the
kvm_init_msr_list() function or create a "common" function that can
be called if the svm/vmx function doesn't directly support the MSR in
question (similar to the get/set msr functions).

Thanks,
Tom

> +	default:
> +		if (kvm_x86_ops->get_msr_feature(&msr))
> +			return 1;
> +	}
>  
>  	*data = msr.data;
>  
> @@ -2248,7 +2255,6 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>  
>  	switch (msr) {
>  	case MSR_AMD64_NB_CFG:
> -	case MSR_IA32_UCODE_REV:
>  	case MSR_IA32_UCODE_WRITE:
>  	case MSR_VM_HSAVE_PA:
>  	case MSR_AMD64_PATCH_LOADER:
> @@ -2256,6 +2262,10 @@ int kvm_set_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>  	case MSR_AMD64_DC_CFG:
>  		break;
>  
> +	case MSR_IA32_UCODE_REV:
> +		if (msr_info->host_initiated)
> +			vcpu->arch.microcode_version = data >> 32;
> +		break;
>  	case MSR_EFER:
>  		return set_efer(vcpu, data);
>  	case MSR_K7_HWCR:
> @@ -2551,7 +2561,7 @@ int kvm_get_msr_common(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>  		msr_info->data = 0;
>  		break;
>  	case MSR_IA32_UCODE_REV:
> -		msr_info->data = 0x100000000ULL;
> +		msr_info->data = (u64)vcpu->arch.microcode_version << 32;
>  		break;
>  	case MSR_MTRRcap:
>  	case 0x200 ... 0x2ff:
> @@ -8233,6 +8243,7 @@ void kvm_vcpu_reset(struct kvm_vcpu *vcpu, bool init_event)
>  	vcpu->arch.regs_dirty = ~0;
>  
>  	vcpu->arch.ia32_xss = 0;
> +	vcpu->arch.microcode_version = 0x1;
>  
>  	kvm_x86_ops->vcpu_reset(vcpu, init_event);
>  }
>