linux-kernel - [PATCH v13 11/21] KVM: x86: Save and reload SSP to/from SMRAM

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Message-ID: <20250821133132.72322-12-chao.gao@intel.com>
Date: Thu, 21 Aug 2025 06:30:45 -0700
From: Chao Gao <chao.gao@...el.com>
To: kvm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: chao.gao@...el.com,
	bp@...en8.de,
	dave.hansen@...ux.intel.com,
	hpa@...or.com,
	john.allen@....com,
	mingo@...hat.com,
	minipli@...ecurity.net,
	mlevitsk@...hat.com,
	pbonzini@...hat.com,
	rick.p.edgecombe@...el.com,
	seanjc@...gle.com,
	tglx@...utronix.de,
	weijiang.yang@...el.com,
	x86@...nel.org,
	xin@...or.com
Subject: [PATCH v13 11/21] KVM: x86: Save and reload SSP to/from SMRAM

From: Yang Weijiang <weijiang.yang@...el.com>

Save CET SSP to SMRAM on SMI and reload it on RSM. KVM emulates HW arch
behavior when guest enters/leaves SMM mode,i.e., save registers to SMRAM
at the entry of SMM and reload them at the exit to SMM. Per SDM, SSP is
one of such registers on 64-bit Arch, and add the support for SSP.

Suggested-by: Sean Christopherson <seanjc@...gle.com>
Signed-off-by: Yang Weijiang <weijiang.yang@...el.com>
Tested-by: Mathias Krause <minipli@...ecurity.net>
Tested-by: John Allen <john.allen@....com>
Tested-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
Signed-off-by: Chao Gao <chao.gao@...el.com>
---
 arch/x86/kvm/smm.c | 8 ++++++++
 arch/x86/kvm/smm.h | 2 +-
 2 files changed, 9 insertions(+), 1 deletion(-)

diff --git a/arch/x86/kvm/smm.c b/arch/x86/kvm/smm.c
index 5dd8a1646800..b0b14ba37f9a 100644
--- a/arch/x86/kvm/smm.c
+++ b/arch/x86/kvm/smm.c
@@ -269,6 +269,10 @@ static void enter_smm_save_state_64(struct kvm_vcpu *vcpu,
 	enter_smm_save_seg_64(vcpu, &smram->gs, VCPU_SREG_GS);
 
 	smram->int_shadow = kvm_x86_call(get_interrupt_shadow)(vcpu);
+
+	if (guest_cpu_cap_has(vcpu, X86_FEATURE_SHSTK) &&
+	    kvm_msr_read(vcpu, MSR_KVM_INTERNAL_GUEST_SSP, &smram->ssp))
+		kvm_make_request(KVM_REQ_TRIPLE_FAULT, vcpu);
 }
 #endif
 
@@ -558,6 +562,10 @@ static int rsm_load_state_64(struct x86_emulate_ctxt *ctxt,
 	kvm_x86_call(set_interrupt_shadow)(vcpu, 0);
 	ctxt->interruptibility = (u8)smstate->int_shadow;
 
+	if (guest_cpu_cap_has(vcpu, X86_FEATURE_SHSTK) &&
+	    kvm_msr_write(vcpu, MSR_KVM_INTERNAL_GUEST_SSP, smstate->ssp))
+		return X86EMUL_UNHANDLEABLE;
+
 	return X86EMUL_CONTINUE;
 }
 #endif
diff --git a/arch/x86/kvm/smm.h b/arch/x86/kvm/smm.h
index 551703fbe200..db3c88f16138 100644
--- a/arch/x86/kvm/smm.h
+++ b/arch/x86/kvm/smm.h
@@ -116,8 +116,8 @@ struct kvm_smram_state_64 {
 	u32 smbase;
 	u32 reserved4[5];
 
-	/* ssp and svm_* fields below are not implemented by KVM */
 	u64 ssp;
+	/* svm_* fields below are not implemented by KVM */
 	u64 svm_guest_pat;
 	u64 svm_host_efer;
 	u64 svm_host_cr4;
-- 
2.47.3