Re: [PATCH v5 13/19] KVM:VMX: Set up interception for CET MSRs

[Chao Gao]

On Thu, Aug 03, 2023 at 12:27:26AM -0400, Yang Weijiang wrote:
>Pass through CET MSRs when the associated feature is enabled.
>Shadow Stack feature requires all the CET MSRs to make it
>architectural support in guest. IBT feature only depends on
>MSR_IA32_U_CET and MSR_IA32_S_CET to enable both user and
>supervisor IBT. Note, This MSR design introduced an architectual
>limitation of SHSTK and IBT control for guest, i.e., when SHSTK
>is exposed, IBT is also available to guest from architectual level
>since IBT relies on subset of SHSTK relevant MSRs.
>
>Signed-off-by: Yang Weijiang <weijiang.yang@xxxxxxxxx>

Reviewed-by: Chao Gao <chao.gao@xxxxxxxxx>

one nit below

>---
> arch/x86/kvm/vmx/vmx.c | 41 +++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 41 insertions(+)
>
>diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
>index ccf750e79608..6779b8a63789 100644
>--- a/arch/x86/kvm/vmx/vmx.c
>+++ b/arch/x86/kvm/vmx/vmx.c
>@@ -709,6 +709,10 @@ static bool is_valid_passthrough_msr(u32 msr)
> 	case MSR_LBR_CORE_TO ... MSR_LBR_CORE_TO + 8:
> 		/* LBR MSRs. These are handled in vmx_update_intercept_for_lbr_msrs() */
> 		return true;
>+	case MSR_IA32_U_CET:
>+	case MSR_IA32_S_CET:
>+	case MSR_IA32_PL0_SSP ... MSR_IA32_INT_SSP_TAB:
>+		return true;
> 	}
> 
> 	r = possible_passthrough_msr_slot(msr) != -ENOENT;
>@@ -7747,6 +7751,41 @@ static void update_intel_pt_cfg(struct kvm_vcpu *vcpu)
> 		vmx->pt_desc.ctl_bitmask &= ~(0xfULL << (32 + i * 4));
> }
> 
>+static void vmx_update_intercept_for_cet_msr(struct kvm_vcpu *vcpu)
>+{
>+	bool incpt;
>+
>+	if (kvm_cpu_cap_has(X86_FEATURE_SHSTK)) {
>+		incpt = !guest_cpuid_has(vcpu, X86_FEATURE_SHSTK);

...

>+
>+		vmx_set_intercept_for_msr(vcpu, MSR_IA32_U_CET,
>+					  MSR_TYPE_RW, incpt);
>+		vmx_set_intercept_for_msr(vcpu, MSR_IA32_S_CET,
>+					  MSR_TYPE_RW, incpt);
>+		vmx_set_intercept_for_msr(vcpu, MSR_IA32_PL0_SSP,
>+					  MSR_TYPE_RW, incpt);
>+		vmx_set_intercept_for_msr(vcpu, MSR_IA32_PL1_SSP,
>+					  MSR_TYPE_RW, incpt);
>+		vmx_set_intercept_for_msr(vcpu, MSR_IA32_PL2_SSP,
>+					  MSR_TYPE_RW, incpt);
>+		vmx_set_intercept_for_msr(vcpu, MSR_IA32_PL3_SSP,
>+					  MSR_TYPE_RW, incpt);
>+		vmx_set_intercept_for_msr(vcpu, MSR_IA32_INT_SSP_TAB,
>+					  MSR_TYPE_RW, incpt);
>+		if (!incpt)
>+			return;
>+	}
>+
>+	if (kvm_cpu_cap_has(X86_FEATURE_IBT)) {
>+		incpt = !guest_can_use(vcpu, X86_FEATURE_IBT);

can you use guest_can_use() or guest_cpuid_has() consistently?

>+
>+		vmx_set_intercept_for_msr(vcpu, MSR_IA32_U_CET,
>+					  MSR_TYPE_RW, incpt);
>+		vmx_set_intercept_for_msr(vcpu, MSR_IA32_S_CET,
>+					  MSR_TYPE_RW, incpt);
>+	}
>+}
>+
> static void vmx_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
> {
> 	struct vcpu_vmx *vmx = to_vmx(vcpu);
>@@ -7814,6 +7853,8 @@ static void vmx_vcpu_after_set_cpuid(struct kvm_vcpu *vcpu)
> 
> 	/* Refresh #PF interception to account for MAXPHYADDR changes. */
> 	vmx_update_exception_bitmap(vcpu);
>+
>+	vmx_update_intercept_for_cet_msr(vcpu);
> }
> 
> static u64 vmx_get_perf_capabilities(void)
>-- 
>2.27.0
>