linux-kernel - Re: [PATCH v28 04/32] x86/cpufeatures: Introduce CPU setup and option parsing for CET

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Date:   Tue, 10 Aug 2021 08:39:00 -0700
From:   "Yu, Yu-cheng" <yu-cheng.yu@...el.com>
To:     Borislav Petkov <bp@...en8.de>
CC:     <x86@...nel.org>, "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, <linux-kernel@...r.kernel.org>,
        <linux-doc@...r.kernel.org>, <linux-mm@...ck.org>,
        <linux-arch@...r.kernel.org>, <linux-api@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Andy Lutomirski <luto@...nel.org>,
        Balbir Singh <bsingharora@...il.com>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        "Eugene Syromiatnikov" <esyr@...hat.com>,
        Florian Weimer <fweimer@...hat.com>,
        "H.J. Lu" <hjl.tools@...il.com>, Jann Horn <jannh@...gle.com>,
        Jonathan Corbet <corbet@....net>,
        Kees Cook <keescook@...omium.org>,
        Mike Kravetz <mike.kravetz@...cle.com>,
        Nadav Amit <nadav.amit@...il.com>,
        Oleg Nesterov <oleg@...hat.com>, Pavel Machek <pavel@....cz>,
        Peter Zijlstra <peterz@...radead.org>,
        Randy Dunlap <rdunlap@...radead.org>,
        "Ravi V. Shankar" <ravi.v.shankar@...el.com>,
        Dave Martin <Dave.Martin@....com>,
        Weijiang Yang <weijiang.yang@...el.com>,
        Pengfei Xu <pengfei.xu@...el.com>,
        Haitao Huang <haitao.huang@...el.com>,
        Rick P Edgecombe <rick.p.edgecombe@...el.com>
Subject: Re: [PATCH v28 04/32] x86/cpufeatures: Introduce CPU setup and option
 parsing for CET

On 8/9/2021 9:06 AM, Borislav Petkov wrote:
> On Thu, Jul 22, 2021 at 01:51:51PM -0700, Yu-cheng Yu wrote:
>>   /*
>>    * Some CPU features depend on higher CPUID levels, which may not always
>>    * be available due to CPUID level capping or broken virtualization
>> @@ -1249,6 +1257,11 @@ static void __init cpu_parse_early_param(void)
>>   	if (cmdline_find_option_bool(boot_command_line, "noxsaves"))
>>   		setup_clear_cpu_cap(X86_FEATURE_XSAVES);
>>   
>> +	if (cmdline_find_option_bool(boot_command_line, "no_user_shstk"))
>> +		setup_clear_cpu_cap(X86_FEATURE_SHSTK);
>> +	if (cmdline_find_option_bool(boot_command_line, "no_user_ibt"))
>> +		setup_clear_cpu_cap(X86_FEATURE_IBT);
> 
> Patch 1 says:
> 
> "Disabling shadow stack also disables IBT."
> 
> I don't see that here.
> 

We have X86_FEATURE_IBT dependent on X86_FEATURE_SHSTK (patch #3).