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

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Message-ID: <bdeb40c0-a17e-4a71-9be2-62ee3ef699a6@linux.intel.com>
Date: Tue, 16 Sep 2025 16:33:09 +0800
From: Binbin Wu <binbin.wu@...ux.intel.com>
To: Sean Christopherson <seanjc@...gle.com>
Cc: Paolo Bonzini <pbonzini@...hat.com>, kvm@...r.kernel.org,
 linux-kernel@...r.kernel.org, Tom Lendacky <thomas.lendacky@....com>,
 Mathias Krause <minipli@...ecurity.net>, John Allen <john.allen@....com>,
 Rick Edgecombe <rick.p.edgecombe@...el.com>, Chao Gao <chao.gao@...el.com>,
 Maxim Levitsky <mlevitsk@...hat.com>, Xiaoyao Li <xiaoyao.li@...el.com>,
 Zhang Yi Z <yi.z.zhang@...ux.intel.com>
Subject: Re: [PATCH v15 10/41] KVM: x86: Add fault checks for guest CR4.CET
 setting



On 9/13/2025 7:22 AM, Sean Christopherson wrote:
> From: Yang Weijiang <weijiang.yang@...el.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@...el.com>
> Reviewed-by: Chao Gao <chao.gao@...el.com>
> Reviewed-by: Maxim Levitsky <mlevitsk@...hat.com>
> Reviewed-by: Xiaoyao Li <xiaoyao.li@...el.com>
> Tested-by: Mathias Krause <minipli@...ecurity.net>
> Tested-by: John Allen <john.allen@....com>
> Tested-by: Rick Edgecombe <rick.p.edgecombe@...el.com>
> Signed-off-by: Chao Gao <chao.gao@...el.com>
> Co-developed-by: Sean Christopherson <seanjc@...gle.com>
> Signed-off-by: Sean Christopherson <seanjc@...gle.com>
Reviewed-by: Binbin Wu <binbin.wu@...ux.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 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);