[PATCH v15 10/41] KVM: x86: Add fault checks for guest CR4.CET setting

Sean Christopherson
2025-09-12T23:23:43Z

From: Yang Weijiang <weijiang.yang@intel.com>

Check potential faults for CR4.CET setting per Intel SDM requirements.
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.

Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
Reviewed-by: Chao Gao <chao.gao@intel.com>
Reviewed-by: Maxim Levitsky <mlevitsk@redhat.com>
Reviewed-by: Xiaoyao Li <xiaoyao.li@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>
Co-developed-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Sean Christopherson <seanjc@google.com>
---
arch/x86/kvm/x86.c | 6 ++++++
1 file changed, 6 insertions(+)

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index a95ca2fbd3a9..5653ddfe124e 100644
--- a/arch/x86/kvm/x86.c
+++ b/arch/x86/kvm/x86.c
@@ -1176,6 +1176,9 @@ int kvm_set_cr0(struct kvm_vcpu *vcpu, unsigned long cr0)
(is_64_bit_mode(vcpu) || kvm_is_cr4_bit_set(vcpu, X86_CR4_PCIDE)))
return 1;

+ if (!(cr0 & X86_CR0_WP) && kvm_is_cr4_bit_set(vcpu, X86_CR4_CET))
+ return 1;
+
kvm_x86_call(set_cr0)(vcpu, cr0);

kvm_post_set_cr0(vcpu, old_cr0, cr0);
@@ -1376,6 +1379,9 @@ int kvm_set_cr4(struct kvm_vcpu *vcpu, unsigned long cr4)
return 1;
}

+ if ((cr4 & X86_CR4_CET) && !kvm_is_cr0_bit_set(vcpu, X86_CR0_WP))
+ return 1;
+
kvm_x86_call(set_cr4)(vcpu, cr4);

kvm_post_set_cr4(vcpu, old_cr4, cr4);
--
2.51.0.384.g4c02a37b29-goog