linux-kernel - [PATCH v15 25/41] KVM: x86: SVM: Emulate reads and writes to shadow stack MSRs

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Message-ID: <20250912232319.429659-26-seanjc@google.com>
Date: Fri, 12 Sep 2025 16:23:03 -0700
From: Sean Christopherson <seanjc@...gle.com>
To: Paolo Bonzini <pbonzini@...hat.com>, Sean Christopherson <seanjc@...gle.com>
Cc: kvm@...r.kernel.org, linux-kernel@...r.kernel.org, 
	Tom Lendacky <thomas.lendacky@....com>, Mathias Krause <minipli@...ecurity.net>, 
	John Allen <john.allen@....com>, Rick Edgecombe <rick.p.edgecombe@...el.com>, 
	Chao Gao <chao.gao@...el.com>, Maxim Levitsky <mlevitsk@...hat.com>, 
	Xiaoyao Li <xiaoyao.li@...el.com>, Zhang Yi Z <yi.z.zhang@...ux.intel.com>
Subject: [PATCH v15 25/41] KVM: x86: SVM: Emulate reads and writes to shadow
 stack MSRs

From: John Allen <john.allen@....com>

Emulate shadow stack MSR access by reading and writing to the
corresponding fields in the VMCB.

Signed-off-by: John Allen <john.allen@....com>
[sean: mark VMCB_CET dirty/clean as appropriate]
Signed-off-by: Sean Christopherson <seanjc@...gle.com>
---
 arch/x86/kvm/svm/svm.c | 21 +++++++++++++++++++++
 arch/x86/kvm/svm/svm.h |  3 ++-
 2 files changed, 23 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/svm/svm.c b/arch/x86/kvm/svm/svm.c
index d4e1fdcf56da..0c0115b52e5c 100644
--- a/arch/x86/kvm/svm/svm.c
+++ b/arch/x86/kvm/svm/svm.c
@@ -2767,6 +2767,15 @@ static int svm_get_msr(struct kvm_vcpu *vcpu, struct msr_data *msr_info)
 		if (guest_cpuid_is_intel_compatible(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_INTERNAL_GUEST_SSP:
+		msr_info->data = svm->vmcb->save.ssp;
+		break;
 	case MSR_TSC_AUX:
 		msr_info->data = svm->tsc_aux;
 		break;
@@ -2999,6 +3008,18 @@ 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_compatible(vcpu) ? (data >> 32) : 0;
 		break;
+	case MSR_IA32_S_CET:
+		svm->vmcb->save.s_cet = data;
+		vmcb_mark_dirty(svm->vmcb01.ptr, VMCB_CET);
+		break;
+	case MSR_IA32_INT_SSP_TAB:
+		svm->vmcb->save.isst_addr = data;
+		vmcb_mark_dirty(svm->vmcb01.ptr, VMCB_CET);
+		break;
+	case MSR_KVM_INTERNAL_GUEST_SSP:
+		svm->vmcb->save.ssp = data;
+		vmcb_mark_dirty(svm->vmcb01.ptr, VMCB_CET);
+		break;
 	case MSR_TSC_AUX:
 		/*
 		 * TSC_AUX is always virtualized for SEV-ES guests when the
diff --git a/arch/x86/kvm/svm/svm.h b/arch/x86/kvm/svm/svm.h
index c2316adde3cc..a42e95883b45 100644
--- a/arch/x86/kvm/svm/svm.h
+++ b/arch/x86/kvm/svm/svm.h
@@ -74,6 +74,7 @@ enum {
 			  * AVIC PHYSICAL_TABLE pointer,
 			  * AVIC LOGICAL_TABLE pointer
 			  */
+	VMCB_CET,	 /* S_CET, SSP, ISST_ADDR */
 	VMCB_SW = 31,    /* Reserved for hypervisor/software use */
 };
 
@@ -82,7 +83,7 @@ enum {
 	(1U << VMCB_ASID) | (1U << VMCB_INTR) |			\
 	(1U << VMCB_NPT) | (1U << VMCB_CR) | (1U << VMCB_DR) |	\
 	(1U << VMCB_DT) | (1U << VMCB_SEG) | (1U << VMCB_CR2) |	\
-	(1U << VMCB_LBR) | (1U << VMCB_AVIC) |			\
+	(1U << VMCB_LBR) | (1U << VMCB_AVIC) | (1U << VMCB_CET) | \
 	(1U << VMCB_SW))
 
 /* TPR and CR2 are always written before VMRUN */
-- 
2.51.0.384.g4c02a37b29-goog