KVM: x86: Add fault checks for CR4.CET

Add the fault checks for CR4.CET, which is the master control for all
CET features (SHSTK and IBT).  In addition to basic support checks, CET
can be enabled if and only if CR0.WP==1, i.e. setting CR4.CET=1 faults
if CR0.WP==0 and setting CR0.WP=0 fails if CR4.CET==1.

Co-developed-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Sean Christopherson <sean.j.christopherson@intel.com>
Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>

arch/x86/kvm/x86.c

@@ -867,6 +867,9 @@ int kvm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)
 	if (!(cr0 & X86_CR0_PG) && kvm_read_cr4_bits(vcpu, X86_CR4_PCIDE))
 		return 1;
 
+	if (!(cr0 & X86_CR0_WP) && kvm_read_cr4_bits(vcpu, X86_CR4_CET))
+		return 1;
+
 	kvm_x86_ops.set_cr0(vcpu, cr0);
 
 	kvm_post_set_cr0(vcpu, old_cr0, cr0);
@@ -1033,6 +1036,9 @@ int kvm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
 			return 1;
 	}
 
+	if ((cr4 & X86_CR4_CET) && !(kvm_read_cr0(vcpu) & X86_CR0_WP))
+		return 1;
+
 	kvm_x86_ops.set_cr4(vcpu, cr4);
 
 	kvm_post_set_cr4(vcpu, old_cr4, cr4);

arch/x86/kvm/x86.h

@@ -425,6 +425,9 @@ bool kvm_msr_allowed(struct kvm_vcpu *vcpu, u32 index, u32 type);
 		__reserved_bits |= X86_CR4_UMIP;        \
 	if (!__cpu_has(__c, X86_FEATURE_VMX))           \
 		__reserved_bits |= X86_CR4_VMXE;        \
+	if (!__cpu_has(__c, X86_FEATURE_SHSTK) &&	\
+	    !__cpu_has(__c, X86_FEATURE_IBT))		\
+		__reserved_bits |= X86_CR4_CET;		\
 	__reserved_bits;                                \
 })