linux-kernel - Re: [RFC PATCH v9 01/27] Documentation/x86: Add CET description

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Message-Id: <2F4A39C5-34EF-4D41-A178-08C34FFA9762@amacapital.net>
Date:   Mon, 9 Mar 2020 15:02:47 -0700
From:   Andy Lutomirski <luto@...capital.net>
To:     "H.J. Lu" <hjl.tools@...il.com>
Cc:     Dave Hansen <dave.hansen@...el.com>,
        Yu-cheng Yu <yu-cheng.yu@...el.com>,
        the arch/x86 maintainers <x86@...nel.org>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        LKML <linux-kernel@...r.kernel.org>, linux-doc@...r.kernel.org,
        Linux-MM <linux-mm@...ck.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Linux API <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>,
        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>, x86-patch-review@...el.com
Subject: Re: [RFC PATCH v9 01/27] Documentation/x86: Add CET description


> On Mar 9, 2020, at 2:13 PM, H.J. Lu <hjl.tools@...il.com> wrote:
> 
> On Mon, Mar 9, 2020 at 1:59 PM Dave Hansen <dave.hansen@...el.com> wrote:
>> 
>> On 3/9/20 1:54 PM, H.J. Lu wrote:
>>>> If a program with the magic ELF CET flags missing can’t make a
>>>> thread with IBT and/or SHSTK enabled, then I think we’ve made an
>>>> error and should fix it.
>>>> 
>>> A non-CET program can start a CET program and vice versa.
>> 
>> Could we be specific here, please?
>> 
>> HJ are you saying that:
>> * CET program can execve() a non-CET program, and
>> * a non-CET program can execve() a CET program
>> 
>> ?
> 
> Yes.
> 
>> That's obvious.
>> 
>> But what are the rules for clone()?  Should there be rules for
>> mismatches for CET enabling between threads if a process (not child
>> processes)?
> 
> What did you mean? A threaded application is either CET enabled or not
> CET enabled.   A new thread from clone makes no difference.

Why?  Dave’s example seems like a good reason to allow per-thread control.



> 
> -- 
> H.J.