linux-kernel - Re: [PATCH v18 24/25] x86/cet/shstk: Add arch

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Message-ID: <8d8bccab-12f3-0ecb-f2b2-91c26f82958a@intel.com>
Date:   Fri, 29 Jan 2021 11:53:01 -0800
From:   "Yu, Yu-cheng" <yu-cheng.yu@...el.com>
To:     Dave Hansen <dave.hansen@...el.com>, 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>,
        Borislav Petkov <bp@...en8.de>,
        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>,
        Vedvyas Shanbhogue <vedvyas.shanbhogue@...el.com>,
        Dave Martin <Dave.Martin@....com>,
        Weijiang Yang <weijiang.yang@...el.com>,
        Pengfei Xu <pengfei.xu@...el.com>
Subject: Re: [PATCH v18 24/25] x86/cet/shstk: Add arch_prctl functions for
 shadow stack

On 1/29/2021 11:15 AM, Dave Hansen wrote:
> On 1/29/21 10:56 AM, Yu, Yu-cheng wrote:
>> On 1/29/2021 9:07 AM, Dave Hansen wrote:
>>> On 1/27/21 1:25 PM, Yu-cheng Yu wrote:
[...]
>>> What's the point of doing copy_status_to_user() if the processor doesn't
>>> support CET?  In other words, shouldn't this be below the CPU feature
>>> check?
>>
>> The thought was to tell the difference between the kernel itself does
>> not support CET and the system does not have CET.  And, if the kernel
>> supports it, show CET status of the thread.
> 
> Why would that matter to userspace?
> 
> If they want to know if the processor has CET support there are existing
> ways to do it.  I don't think this should be part of the ABI.
> 

Ok, I will make it:

if (!cpu_feature_enabled(X86_FEATURE_CET))
	...