[PATCH v16 15/51] KVM: x86: Save and reload SSP to/from SMRAM

Sean Christopherson
2025-09-19T22:33:33Z

From: Yang Weijiang <weijiang.yang@intel.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@google.com>
Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
Tested-by: Mathias Krause <minipli@grsecurity.net>
Tested-by: John Allen <john.allen@amd.com>
Tested-by: Rick Edgecombe <rick.p.edgecombe@intel.com>
Signed-off-by: Chao Gao <chao.gao@intel.com>
Reviewed-by: Binbin Wu <binbin.wu@linux.intel.com>
Reviewed-by: Xiaoyao Li <xiaoyao.li@intel.com>
Signed-off-by: Sean Christopherson <seanjc@google.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;
--
2.51.0.470.ga7dc726c21-goog