linux-kernel - Re: [PATCH v5 07/27] mm/mmap: Create a guard area between VMAs

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Message-ID: <87va67799i.fsf@mid.deneb.enyo.de>
Date:   Fri, 12 Oct 2018 12:24:25 +0200
From:   Florian Weimer <fw@...eb.enyo.de>
To:     Dave Hansen <dave.hansen@...ux.intel.com>
Cc:     Yu-cheng Yu <yu-cheng.yu@...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@...capital.net>,
        Balbir Singh <bsingharora@...il.com>,
        Cyrill Gorcunov <gorcunov@...il.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>
Subject: Re: [PATCH v5 07/27] mm/mmap: Create a guard area between VMAs

* Dave Hansen:

> On 10/11/2018 08:15 AM, Yu-cheng Yu wrote:
>> Create a guard area between VMAs to detect memory corruption.
>
> This is a pretty major change that has a bunch of end-user implications.
>  It's not dependent on any debugging options and can't be turned on/off
> by individual apps, at runtime, or even at boot.
>
> Its connection to this series is also tenuous and not spelled out in the
> exceptionally terse changelog.

I agree.  We did have application failures due to the introduction of
the stack gap, so this change is likely to cause failures when applied
to existing mappings as well.