KVM: x86: Save and reload SSP to/from SMRAM

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>
Link: https://lore.kernel.org/r/20250919223258.1604852-16-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

diff --git a/arch/x86/kvm/smm.c b/arch/x86/kvm/smm.c
index 5dd8a16468006ccf51ca9d6599fc84ed216c1ca9..b0b14ba37f9ab26726d65f9b2318001b18a31274 100644 (file)
--- 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 551703fbe200ce56adcf29cc817ee4ea7bc39051..db3c88f16138942039372640c895b150b546a7e5 100644 (file)
--- 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;