linux-kernel - [PATCH v2 2/9] KVM: x86: SVM: Emulate reads and writes to shadow stack MSRs

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Date: Mon, 26 Feb 2024 21:32:37 +0000
From: John Allen <john.allen@....com>
To: <kvm@...r.kernel.org>
CC: <weijiang.yang@...el.com>, <rick.p.edgecombe@...el.com>,
	<seanjc@...gle.com>, <thomas.lendacky@....com>, <bp@...en8.de>,
	<pbonzini@...hat.com>, <mlevitsk@...hat.com>, <linux-kernel@...r.kernel.org>,
	<x86@...nel.org>, John Allen <john.allen@....com>
Subject: [PATCH v2 2/9] KVM: x86: SVM: Emulate reads and writes to shadow stack MSRs

Set up interception of shadow stack MSRs. In the event that shadow stack
is unsupported on the host or the MSRs are otherwise inaccessible, the
interception code will return an error. In certain circumstances such as
host initiated MSR reads or writes, the interception code will get or
set the requested MSR value.

Signed-off-by: John Allen <john.allen@....com>
---
 arch/x86/kvm/svm/svm.c | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index e90b429c84f1..70f6fb1a166b 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -2864,6 +2864,15 @@ static int svm_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		if (guest_cpuid_is_intel(vcpu))
 			msr_info->data |= (u64)svm->sysenter_esp_hi << 32;
 		break;
+	case MSR_IA32_S_CET:
+		msr_info->data = svm->vmcb->save.s_cet;
+		break;
+	case MSR_IA32_INT_SSP_TAB:
+		msr_info->data = svm->vmcb->save.isst_addr;
+		break;
+	case MSR_KVM_SSP:
+		msr_info->data = svm->vmcb->save.ssp;
+		break;
 	case MSR_TSC_AUX:
 		msr_info->data = svm->tsc_aux;
 		break;
@@ -3090,6 +3099,15 @@ static int svm_set_msr(struct kvm_vcpu *vcpu, struct msr_data *msr)
 		svm->vmcb01.ptr->save.sysenter_esp = (u32)data;
 		svm->sysenter_esp_hi = guest_cpuid_is_intel(vcpu) ? (data >> 32) : 0;
 		break;
+	case MSR_IA32_S_CET:
+		svm->vmcb->save.s_cet = data;
+		break;
+	case MSR_IA32_INT_SSP_TAB:
+		svm->vmcb->save.isst_addr = data;
+		break;
+	case MSR_KVM_SSP:
+		svm->vmcb->save.ssp = data;
+		break;
 	case MSR_TSC_AUX:
 		/*
 		 * TSC_AUX is always virtualized for SEV-ES guests when the
-- 
2.40.1