KVM: x86: Add fault checks for guest CR4.CET setting

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>
Reviewed-by: Binbin Wu <binbin.wu@linux.intel.com>
Co-developed-by: Sean Christopherson <seanjc@google.com>
Link: https://lore.kernel.org/r/20250919223258.1604852-11-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>

diff --git a/arch/x86/kvm/x86.c b/arch/x86/kvm/x86.c
index c2e11f3d50fbbaded0607541ab4c867cacda5c45..6d67c969e18a089c14a9c4ff7a212c6069916afb 100644 (file)
--- 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);