Re: [PATCH v7 7/7] KVM: x86: Add user-space access interface for CET MSRs

[Jim Mattson <jmattson@google.com>]

On Thu, Sep 26, 2019 at 7:17 PM Yang Weijiang <weijiang.yang@intel.com> wrote:
>
> There're two different places storing Guest CET states, the states
> managed with XSAVES/XRSTORS, as restored/saved
> in previous patch, can be read/write directly from/to the MSRs.
> For those stored in VMCS fields, they're access via vmcs_read/
> vmcs_write.
>
> Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
> ---
>  arch/x86/kvm/vmx/vmx.c | 83 ++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 83 insertions(+)
>
> diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
> index 44913e4ab558..5265db7cd2af 100644
> --- a/arch/x86/kvm/vmx/vmx.c
> +++ b/arch/x86/kvm/vmx/vmx.c
> @@ -1671,6 +1671,49 @@ static int vmx_get_msr_feature(struct kvm_msr_entry *msr)
>         return 0;
>  }
>
> +static int check_cet_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)

I'd suggest changing return type to bool, since you are essentially
returning true or false.

> +{
> +       u64 kvm_xss = kvm_supported_xss();
> +
> +       switch (msr_info->index) {
> +       case MSR_IA32_PL0_SSP ... MSR_IA32_PL2_SSP:
> +               if (!(kvm_xss | XFEATURE_MASK_CET_KERNEL))
'|' should be '&'
> +                       return 1;
> +               if (!msr_info->host_initiated &&
> +                   !guest_cpuid_has(vcpu, X86_FEATURE_SHSTK))
> +                       return 1;
> +               break;
> +       case MSR_IA32_PL3_SSP:
> +               if (!(kvm_xss | XFEATURE_MASK_CET_USER))
'|' should be '&'
> +                       return 1;
> +               if (!msr_info->host_initiated &&
> +                   !guest_cpuid_has(vcpu, X86_FEATURE_SHSTK))
> +                       return 1;
> +               break;
> +       case MSR_IA32_U_CET:
> +               if (!(kvm_xss | XFEATURE_MASK_CET_USER))
'|' should be '&'
> +                       return 1;
> +               if (!msr_info->host_initiated &&
> +                   !guest_cpuid_has(vcpu, X86_FEATURE_SHSTK) &&
> +                   !guest_cpuid_has(vcpu, X86_FEATURE_IBT))
> +                       return 1;
> +               break;
> +       case MSR_IA32_S_CET:
> +               if (!msr_info->host_initiated &&
> +                   !guest_cpuid_has(vcpu, X86_FEATURE_SHSTK) &&
> +                   !guest_cpuid_has(vcpu, X86_FEATURE_IBT))
> +                       return 1;
> +               break;
> +       case MSR_IA32_INT_SSP_TAB:
> +               if (!msr_info->host_initiated &&
> +                   !guest_cpuid_has(vcpu, X86_FEATURE_SHSTK))
> +                       return 1;
> +               break;
> +       default:
> +               return 1;
> +       }
> +       return 0;
> +}
>  /*
>   * Reads an msr value (of 'msr_index') into 'pdata'.
>   * Returns 0 on success, non-0 otherwise.
> @@ -1788,6 +1831,26 @@ static int vmx_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>                 else
>                         msr_info->data = vmx->pt_desc.guest.addr_a[index / 2];
>                 break;
> +       case MSR_IA32_S_CET:
> +               if (check_cet_msr(vcpu, msr_info))
> +                       return 1;
> +               msr_info->data = vmcs_readl(GUEST_S_CET);
Have we ensured that this VMCS field exists?
> +               break;
> +       case MSR_IA32_INT_SSP_TAB:
> +               if (check_cet_msr(vcpu, msr_info))
> +                       return 1;
> +               msr_info->data = vmcs_readl(GUEST_INTR_SSP_TABLE);
Have we ensured that this VMCS field exists?
> +               break;
> +       case MSR_IA32_U_CET:
Can this be lumped together with MSR_IA32_PL0_SSP ... MSR_IA32_PL3_SSP, below?
> +               if (check_cet_msr(vcpu, msr_info))
> +                       return 1;
> +               rdmsrl(MSR_IA32_U_CET, msr_info->data);
> +               break;
> +       case MSR_IA32_PL0_SSP ... MSR_IA32_PL3_SSP:
> +               if (check_cet_msr(vcpu, msr_info))
> +                       return 1;
> +               rdmsrl(msr_info->index, msr_info->data);
> +               break;
>         case MSR_TSC_AUX:
>                 if (!msr_info->host_initiated &&
>                     !guest_cpuid_has(vcpu, X86_FEATURE_RDTSCP))
> @@ -2039,6 +2102,26 @@ static int vmx_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
>                 else
>                         vmx->pt_desc.guest.addr_a[index / 2] = data;
>                 break;
> +       case MSR_IA32_S_CET:
> +               if (check_cet_msr(vcpu, msr_info))
> +                       return 1;
Bits 9:6 must be zero.
> +               vmcs_writel(GUEST_S_CET, data);
Have we ensured that this VMCS field exists?
> +               break;
> +       case MSR_IA32_INT_SSP_TAB:
> +               if (check_cet_msr(vcpu, msr_info))
> +                       return 1;
Must be canonical. vCPU must support longmode.
> +               vmcs_writel(GUEST_INTR_SSP_TABLE, data);
Have we ensured that this VMCS field exists?
> +               break;
> +       case MSR_IA32_U_CET:
> +               if (check_cet_msr(vcpu, msr_info))
> +                       return 1;
Bits 9:6 must be zero.
> +               wrmsrl(MSR_IA32_U_CET, data);
> +               break;
> +       case MSR_IA32_PL0_SSP ... MSR_IA32_PL3_SSP:
> +               if (check_cet_msr(vcpu, msr_info))
> +                       return 1;
'Data' must be canonical and 4-byte aligned. High dword must be zero
on vCPUs that don't support longmode.
> +               wrmsrl(msr_info->index, data);
> +               break;
>         case MSR_TSC_AUX:
>                 if (!msr_info->host_initiated &&
>                     !guest_cpuid_has(vcpu, X86_FEATURE_RDTSCP))
> --
> 2.17.2
>