linux-kernel - Re: [PATCH v3 12/21] KVM:x86: Add fault checks for guest CR4.CET setting

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Date:   Thu, 8 Jun 2023 14:06:48 +0800
From:   "Yang, Weijiang" <weijiang.yang@...el.com>
To:     Chao Gao <chao.gao@...el.com>
CC:     <seanjc@...gle.com>, <pbonzini@...hat.com>, <kvm@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <peterz@...radead.org>,
        <rppt@...nel.org>, <binbin.wu@...ux.intel.com>,
        <rick.p.edgecombe@...el.com>, <john.allen@....com>,
        Sean Christopherson <sean.j.christopherson@...el.com>
Subject: Re: [PATCH v3 12/21] KVM:x86: Add fault checks for guest CR4.CET
 setting


On 6/6/2023 7:03 PM, Chao Gao wrote:
> On Thu, May 11, 2023 at 12:08:48AM -0400, Yang Weijiang wrote:
>> Check potential faults for CR4.CET setting per Intel SDM.
>> CR4.CET is the master control bit for CET features (SHSTK and IBT).
>> In addition to basic support checks,
> To me, this implies some checks against CR4.CET when enabling SHSTK or
> IBT. but the checks are not added by this patch. Then, why bother to
> mention this?

OK, I'll remove these unnecessary words and change the commit logs.

>
>> 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@...el.com>
>> Signed-off-by: Sean Christopherson <sean.j.christopherson@...el.com>
>> Signed-off-by: Yang Weijiang <weijiang.yang@...el.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 a768cbf3fbb7..b6eec9143129 100644
>> --- a/arch/x86/kvm/x86.c
>> +++ b/arch/x86/kvm/x86.c
>> @@ -995,6 +995,9 @@ 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;
>> +
>> 	static_call(kvm_x86_set_cr0)(vcpu, cr0);
>>
>> 	kvm_post_set_cr0(vcpu, old_cr0, cr0);
>> @@ -1210,6 +1213,9 @@ 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;
>> +
>> 	static_call(kvm_x86_set_cr4)(vcpu, cr4);
>>
>> 	kvm_post_set_cr4(vcpu, old_cr4, cr4);
>> -- 
>> 2.27.0
>>