linux-kernel - Re: [PATCH v14 15/22] KVM: x86: Don't emulate instructions guarded by CET

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [day] [month] [year] [list]

Message-ID: <aMKniY+GguBPe8tK@intel.com>
Date: Thu, 11 Sep 2025 18:42:17 +0800
From: Chao Gao <chao.gao@...el.com>
To: Xiaoyao Li <xiaoyao.li@...el.com>
CC: <kvm@...r.kernel.org>, <linux-kernel@...r.kernel.org>, <acme@...hat.com>,
	<bp@...en8.de>, <dave.hansen@...ux.intel.com>, <hpa@...or.com>,
	<john.allen@....com>, <mingo@...nel.org>, <mingo@...hat.com>,
	<minipli@...ecurity.net>, <mlevitsk@...hat.com>, <namhyung@...nel.org>,
	<pbonzini@...hat.com>, <prsampat@....com>, <rick.p.edgecombe@...el.com>,
	<seanjc@...gle.com>, <shuah@...nel.org>, <tglx@...utronix.de>,
	<weijiang.yang@...el.com>, <x86@...nel.org>, <xin@...or.com>
Subject: Re: [PATCH v14 15/22] KVM: x86: Don't emulate instructions guarded
 by CET

>> @@ -4941,6 +4947,24 @@ int x86_decode_insn(struct x86_emulate_ctxt *ctxt, void *insn, int insn_len, int
>>   	if (ctxt->d == 0)
>>   		return EMULATION_FAILED;
>> +	if (ctxt->ops->get_cr(ctxt, 4) & X86_CR4_CET) {
>> +		u64 u_cet, s_cet;
>> +		bool stop_em;
>> +
>> +		if (ctxt->ops->get_msr(ctxt, MSR_IA32_U_CET, &u_cet) ||
>> +		    ctxt->ops->get_msr(ctxt, MSR_IA32_S_CET, &s_cet))
>> +			return EMULATION_FAILED;
>> +
>> +		stop_em = ((u_cet & CET_SHSTK_EN) || (s_cet & CET_SHSTK_EN)) &&
>> +			  (opcode.flags & ShadowStack);
>> +
>> +		stop_em |= ((u_cet & CET_ENDBR_EN) || (s_cet & CET_ENDBR_EN)) &&
>> +			   (opcode.flags & IndirBrnTrk);
>
>Why don't check CPL here? Just for simplicity?

I think so. This is a corner case and we don't want to make it very precise
(and thus complex). The reason is that no one had a strong opinion on whether
to do the CPL check or not. I asked the same question before [*], but I don't
have a strong opinion on this either.

[*]: https://lore.kernel.org/kvm/ZaSQn7RCRTaBK1bc@chao-email/