Re: [PATCH v14 07/22] KVM: x86: Add fault checks for guest CR4.CET setting

[Xiaoyao Li <xiaoyao.li@intel.com>]

On 9/9/2025 5:39 PM, Chao Gao wrote:
> 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.
> 
> Co-developed-by: Sean Christopherson <seanjc@google.com>
> Signed-off-by: Sean Christopherson <seanjc@google.com>
> Signed-off-by: Yang Weijiang <weijiang.yang@intel.com>
> Reviewed-by: Chao Gao <chao.gao@intel.com>
> Reviewed-by: Maxim Levitsky <mlevitsk@redhat.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: Xiaoyao Li <xiaoyao.li@intel.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 7c0a07be6b64..50c192c99a7e 100644
> --- a/arch/x86/kvm/x86.c
> +++ b/arch/x86/kvm/x86.c
> @@ -1173,6 +1173,9 @@ 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);
> @@ -1372,6 +1375,9 @@ 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);