Re: [PATCH v2 5/7] KVM: VMX: Disallow PT MSRs accessing if PT is not exposed to guest

[Paolo Bonzini <pbonzini@xxxxxxxxxx>]

On 27/08/21 09:02, Xiaoyao Li wrote:
> Per SDM, it triggers #GP for all the accessing of PT MSRs, if
> X86_FEATURE_INTEL_PT is not available.
>
> Signed-off-by: Xiaoyao Li <xiaoyao.li@xxxxxxxxx>
> ---
> Changes in v2:
>   - allow userspace/host access regradless of PT bit, (Sean)
> ---
>   arch/x86/kvm/vmx/vmx.c | 38 +++++++++++++++++++++++++-------------
>   1 file changed, 25 insertions(+), 13 deletions(-)

Let's cache this in vmx->pt_desc.  More precisely:

- always call update_intel_pt_cfg from vmx_vcpu_after_set_cpuid

- add a field vmx->pt_desc.available matching guest_cpuid_has(vcpu, 
X86_FEATURE_INTEL_PT)

- if it is false, clear _all_ of vmx->pt_desc (with memcpy) and return 
early from update_intel_pt_cfg

Thanks,

Paolo

> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index b9d640029c40..394ef4732838 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -1007,10 +1007,21 @@ static unsigned long segment_base(u16 selector)
>   }
>   #endif
>   
> -static inline bool pt_can_write_msr(struct vcpu_vmx *vmx)
> +static inline bool pt_can_write_msr(struct vcpu_vmx *vmx,
> +				    struct msr_data *msr_info)
>   {
>   	return vmx_pt_mode_is_host_guest() &&
> -	       !(vmx->pt_desc.guest.ctl & RTIT_CTL_TRACEEN);
> +	       !(vmx->pt_desc.guest.ctl & RTIT_CTL_TRACEEN) &&
> +	       (msr_info->host_initiated ||
> +		guest_cpuid_has(&vmx->vcpu, X86_FEATURE_INTEL_PT));
> +}
> +
> +static inline bool pt_can_read_msr(struct kvm_vcpu *vcpu,
> +				   struct msr_data *msr_info)
> +{
> +	return vmx_pt_mode_is_host_guest() &&
> +	       (msr_info->host_initiated ||
> +		guest_cpuid_has(vcpu, X86_FEATURE_INTEL_PT));
>   }
>   
>   static inline bool pt_output_base_valid(struct kvm_vcpu *vcpu, u64 base)
> @@ -1852,24 +1863,24 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>   							&msr_info->data);
>   		break;
>   	case MSR_IA32_RTIT_CTL:
> -		if (!vmx_pt_mode_is_host_guest())
> +		if (!pt_can_read_msr(vcpu, msr_info))
>   			return 1;
>   		msr_info->data = vmx->pt_desc.guest.ctl;
>   		break;
>   	case MSR_IA32_RTIT_STATUS:
> -		if (!vmx_pt_mode_is_host_guest())
> +		if (!pt_can_read_msr(vcpu, msr_info))
>   			return 1;
>   		msr_info->data = vmx->pt_desc.guest.status;
>   		break;
>   	case MSR_IA32_RTIT_CR3_MATCH:
> -		if (!vmx_pt_mode_is_host_guest() ||
> +		if (!pt_can_read_msr(vcpu, msr_info) ||
>   			!intel_pt_validate_cap(vmx->pt_desc.caps,
>   						PT_CAP_cr3_filtering))
>   			return 1;
>   		msr_info->data = vmx->pt_desc.guest.cr3_match;
>   		break;
>   	case MSR_IA32_RTIT_OUTPUT_BASE:
> -		if (!vmx_pt_mode_is_host_guest() ||
> +		if (!pt_can_read_msr(vcpu, msr_info) ||
>   			(!intel_pt_validate_cap(vmx->pt_desc.caps,
>   					PT_CAP_topa_output) &&
>   			 !intel_pt_validate_cap(vmx->pt_desc.caps,
> @@ -1878,7 +1889,7 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>   		msr_info->data = vmx->pt_desc.guest.output_base;
>   		break;
>   	case MSR_IA32_RTIT_OUTPUT_MASK:
> -		if (!vmx_pt_mode_is_host_guest() ||
> +		if (!pt_can_read_msr(vcpu, msr_info) ||
>   			(!intel_pt_validate_cap(vmx->pt_desc.caps,
>   					PT_CAP_topa_output) &&
>   			 !intel_pt_validate_cap(vmx->pt_desc.caps,
> @@ -1888,7 +1899,7 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>   		break;
>   	case MSR_IA32_RTIT_ADDR0_A ... MSR_IA32_RTIT_ADDR3_B:
>   		index = msr_info->index - MSR_IA32_RTIT_ADDR0_A;
> -		if (!vmx_pt_mode_is_host_guest() ||
> +		if (!pt_can_read_msr(vcpu, msr_info) ||
>   		    (index >= 2 * vmx->pt_desc.nr_addr_ranges))
>   			return 1;
>   		if (index % 2)
> @@ -2156,6 +2167,7 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>   		return vmx_set_vmx_msr(vcpu, msr_index, data);
>   	case MSR_IA32_RTIT_CTL:
>   		if (!vmx_pt_mode_is_host_guest() ||
> +		    !guest_cpuid_has(vcpu, X86_FEATURE_INTEL_PT) ||
>   			vmx_rtit_ctl_check(vcpu, data) ||
>   			vmx->nested.vmxon)
>   			return 1;
> @@ -2164,14 +2176,14 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>   		pt_update_intercept_for_msr(vcpu);
>   		break;
>   	case MSR_IA32_RTIT_STATUS:
> -		if (!pt_can_write_msr(vmx))
> +		if (!pt_can_write_msr(vmx, msr_info))
>   			return 1;
>   		if (data & MSR_IA32_RTIT_STATUS_MASK)
>   			return 1;
>   		vmx->pt_desc.guest.status = data;
>   		break;
>   	case MSR_IA32_RTIT_CR3_MATCH:
> -		if (!pt_can_write_msr(vmx))
> +		if (!pt_can_write_msr(vmx, msr_info))
>   			return 1;
>   		if (!intel_pt_validate_cap(vmx->pt_desc.caps,
>   					   PT_CAP_cr3_filtering))
> @@ -2179,7 +2191,7 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>   		vmx->pt_desc.guest.cr3_match = data;
>   		break;
>   	case MSR_IA32_RTIT_OUTPUT_BASE:
> -		if (!pt_can_write_msr(vmx))
> +		if (!pt_can_write_msr(vmx, msr_info))
>   			return 1;
>   		if (!intel_pt_validate_cap(vmx->pt_desc.caps,
>   					   PT_CAP_topa_output) &&
> @@ -2191,7 +2203,7 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>   		vmx->pt_desc.guest.output_base = data;
>   		break;
>   	case MSR_IA32_RTIT_OUTPUT_MASK:
> -		if (!pt_can_write_msr(vmx))
> +		if (!pt_can_write_msr(vmx, msr_info))
>   			return 1;
>   		if (!intel_pt_validate_cap(vmx->pt_desc.caps,
>   					   PT_CAP_topa_output) &&
> @@ -2201,7 +2213,7 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>   		vmx->pt_desc.guest.output_mask = data;
>   		break;
>   	case MSR_IA32_RTIT_ADDR0_A ... MSR_IA32_RTIT_ADDR3_B:
> -		if (!pt_can_write_msr(vmx))
> +		if (!pt_can_write_msr(vmx, msr_info))
>   			return 1;
>   		index = msr_info->index - MSR_IA32_RTIT_ADDR0_A;
>   		if (index >= 2 * vmx->pt_desc.nr_addr_ranges)