Re: [PATCH v15 15/41] KVM: x86: Save and reload SSP to/from SMRAM

[Binbin Wu <binbin.wu@linux.intel.com>]

On 9/13/2025 7:22 AM, Sean Christopherson wrote:
> 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>
> Signed-off-by: Sean Christopherson <seanjc@google.com>

Reviewed-by: Binbin Wu <binbin.wu@linux.intel.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;