[PATCH v5 5/8] KVM: VMX: Load Guest CET via VMCS when CET is enabled in Guest

[Yang Weijiang]

"Load Guest CET state" bit controls whether Guest CET states
will be loaded at Guest entry. Before doing that, KVM needs
to check if CPU CET feature is available to Guest.

Note: SHSTK and IBT features share one control MSR:
MSR_IA32_{U,S}_CET, which means it's difficult to hide
one feature from another in the case of SHSTK != IBT,
after discussed in community, it's agreed to allow Guest
control two features independently as it won't introduce
security hole.

Signed-off-by: Yang Weijiang <weijiang.yang@xxxxxxxxx>
Co-developed-by: Zhang Yi Z <yi.z.zhang@xxxxxxxxxxxxxxx>
---
 arch/x86/kvm/vmx/vmx.c | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/arch/x86/kvm/vmx/vmx.c b/arch/x86/kvm/vmx/vmx.c
index 9321da538f65..1c0d487a4037 100644
--- a/arch/x86/kvm/vmx/vmx.c
+++ b/arch/x86/kvm/vmx/vmx.c
@@ -47,6 +47,7 @@
 #include <asm/spec-ctrl.h>
 #include <asm/virtext.h>
 #include <asm/vmx.h>
+#include <asm/cet.h>
 
 #include "capabilities.h"
 #include "cpuid.h"
@@ -2929,6 +2930,17 @@ int vmx_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
 		if (!nested_vmx_allowed(vcpu) || is_smm(vcpu))
 			return 1;
 	}
+	if (guest_cpuid_has(vcpu, X86_FEATURE_SHSTK) ||
+	    guest_cpuid_has(vcpu, X86_FEATURE_IBT)) {
+		if (cr4 & X86_CR4_CET)
+			vmcs_set_bits(VM_ENTRY_CONTROLS,
+				      VM_ENTRY_LOAD_GUEST_CET_STATE);
+		else
+			vmcs_clear_bits(VM_ENTRY_CONTROLS,
+					VM_ENTRY_LOAD_GUEST_CET_STATE);
+	} else if (cr4 & X86_CR4_CET) {
+		return 1;
+	}
 
 	if (to_vmx(vcpu)->nested.vmxon && !nested_cr4_valid(vcpu, cr4))
 		return 1;
-- 
2.17.2