[PATCH 15/19] KVM: x86: Save/Restore GUEST_SSP to/from SMM state save area

[Yang Weijiang]

Save GUEST_SSP in the SMM state save area when guest exits to SMM
due to SMI and restore it when guest exits SMM.

Signed-off-by: Yang Weijiang <weijiang.yang@xxxxxxxxx>
Message-Id: <20210203113421.5759-15-weijiang.yang@xxxxxxxxx>
[Change the SMM offset to some place that is actually free. - Paolo]
Signed-off-by: Paolo Bonzini <pbonzini@xxxxxxxxxx>
---
 arch/x86/kvm/emulate.c | 11 +++++++++++
 arch/x86/kvm/x86.c     | 10 ++++++++++
 2 files changed, 21 insertions(+)

diff --git a/arch/x86/kvm/emulate.c b/arch/x86/kvm/emulate.c
index 39ea9138224c..eb0d45ae5214 100644
--- a/arch/x86/kvm/emulate.c
+++ b/arch/x86/kvm/emulate.c
@@ -2558,6 +2558,17 @@ static int rsm_load_state_64(struct x86_emulate_ctxt *ctxt,
 			return r;
 	}
 
+	if (kvm_cet_user_supported()) {
+		struct msr_data msr;
+
+		val = GET_SMSTATE(u64, smstate, 0x7f08);
+		msr.index = MSR_KVM_GUEST_SSP;
+		msr.host_initiated = true;
+		msr.data = val;
+		/* Mimic host_initiated access to bypass ssp access check. */
+		kvm_x86_ops.set_msr(ctxt->vcpu, &msr);
+	}
+
 	return X86EMUL_CONTINUE;
 }
 #endif
diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index 3613b73f13fb..86bccb12f036 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -9833,6 +9833,16 @@ static void enter_smm_save_state_64(struct kvm_vcpu *vcpu, char *buf)
 
 	for (i = 0; i < 6; i++)
 		enter_smm_save_seg_64(vcpu, buf, i);
+
+	if (kvm_cet_user_supported()) {
+		struct msr_data msr;
+
+		msr.index = MSR_KVM_GUEST_SSP;
+		msr.host_initiated = true;
+		/* GUEST_SSP is stored in VMCS at vm-exit. */
+		kvm_x86_ops.get_msr(vcpu, &msr);
+		put_smstate(u64, buf, 0x7f08, msr.data);
+	}
 }
 #endif
 
-- 
2.27.0