[PATCH v15 06/14] KVM: x86: Add fault checks for CR4.CET

[Yang Weijiang]

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@xxxxxxxxx>
Signed-off-by: Sean Christopherson <sean.j.christopherson@xxxxxxxxx>
Signed-off-by: Yang Weijiang <weijiang.yang@xxxxxxxxx>
---
 arch/x86/kvm/x86.c | 6 ++++++
 arch/x86/kvm/x86.h | 3 +++
 2 files changed, 9 insertions(+)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index d9d3bae40a8c..6af240d87a33 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -868,6 +868,9 @@ 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);
@@ -1034,6 +1037,9 @@ 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);
diff --git a/arch/x86/kvm/x86.h b/arch/x86/kvm/x86.h
index bdbd0b023ecc..fd8c46da2030 100644
--- a/arch/x86/kvm/x86.h
+++ b/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;                                \
 })
 
-- 
2.26.2