Commit c5ba4945 authored by Sean Christopherson's avatar Sean Christopherson
Browse files

KVM: nSVM: Save/load CET Shadow Stack state to/from vmcb12/vmcb02 

Transfer the three CET Shadow Stack VMCB fields (S_CET, ISST_ADDR, and
SSP) on VMRUN, #VMEXIT, and loading nested state (saving nested state
simply copies the entire save area).  SVM doesn't provide a way to
disallow L1 from enabling Shadow Stacks for L2, i.e. KVM *must* provide
nested support before advertising SHSTK to userspace.

Link: https://lore.kernel.org/r/20250919223258.1604852-37-seanjc@google.com


Signed-off-by: default avatarSean Christopherson <seanjc@google.com>
parent 48b2ec0d

arch/x86/kvm/svm/nested.c

+20 −0
Original line number Diff line number Diff line
@@ -636,6 +636,14 @@ static void nested_vmcb02_prepare_save(struct vcpu_svm *svm, struct vmcb *vmcb12 
		vmcb_mark_dirty(vmcb02, VMCB_DT);

	}



	if (guest_cpu_cap_has(vcpu, X86_FEATURE_SHSTK) &&

	    (unlikely(new_vmcb12 || vmcb_is_dirty(vmcb12, VMCB_CET)))) {

		vmcb02->save.s_cet  = vmcb12->save.s_cet;

		vmcb02->save.isst_addr = vmcb12->save.isst_addr;

		vmcb02->save.ssp = vmcb12->save.ssp;

		vmcb_mark_dirty(vmcb02, VMCB_CET);

	}



	kvm_set_rflags(vcpu, vmcb12->save.rflags | X86_EFLAGS_FIXED);



	svm_set_efer(vcpu, svm->nested.save.efer);
@@ -1044,6 +1052,12 @@ void svm_copy_vmrun_state(struct vmcb_save_area *to_save, 
	to_save->rsp = from_save->rsp;

	to_save->rip = from_save->rip;

	to_save->cpl = 0;



	if (kvm_cpu_cap_has(X86_FEATURE_SHSTK)) {

		to_save->s_cet  = from_save->s_cet;

		to_save->isst_addr = from_save->isst_addr;

		to_save->ssp = from_save->ssp;

	}

}



void svm_copy_vmloadsave_state(struct vmcb *to_vmcb, struct vmcb *from_vmcb)
@@ -1111,6 +1125,12 @@ int nested_svm_vmexit(struct vcpu_svm *svm) 
	vmcb12->save.dr6    = svm->vcpu.arch.dr6;

	vmcb12->save.cpl    = vmcb02->save.cpl;



	if (guest_cpu_cap_has(vcpu, X86_FEATURE_SHSTK)) {

		vmcb12->save.s_cet	= vmcb02->save.s_cet;

		vmcb12->save.isst_addr	= vmcb02->save.isst_addr;

		vmcb12->save.ssp	= vmcb02->save.ssp;

	}



	vmcb12->control.int_state         = vmcb02->control.int_state;

	vmcb12->control.exit_code         = vmcb02->control.exit_code;

	vmcb12->control.exit_code_hi      = vmcb02->control.exit_code_hi;