linux-kernel - Re: [RFC PATCH v4 24/27] mm/mmap: Create a guard area between VMAs

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Date:   Tue, 2 Oct 2018 22:36:15 -0700
From:   Andy Lutomirski <luto@...capital.net>
To:     Eugene Syromiatnikov <esyr@...hat.com>
Cc:     Yu-cheng Yu <yu-cheng.yu@...el.com>, X86 ML <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>,
        Balbir Singh <bsingharora@...il.com>,
        Cyrill Gorcunov <gorcunov@...il.com>,
        Dave Hansen <dave.hansen@...ux.intel.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>,
        "Shanbhogue, Vedvyas" <vedvyas.shanbhogue@...el.com>
Subject: Re: [RFC PATCH v4 24/27] mm/mmap: Create a guard area between VMAs

On Tue, Oct 2, 2018 at 9:55 PM Eugene Syromiatnikov <esyr@...hat.com> wrote:
>
> On Fri, Sep 21, 2018 at 08:03:48AM -0700, Yu-cheng Yu wrote:
> > Create a guard area between VMAs, to detect memory corruption.
>
> Do I understand correctly that with this patch a user space program
> no longer be able to place two mappings back to back? If it is so,
> it will likely break a lot of things; for example, it's a common ring
> buffer implementations technique, to map buffer memory twice back
> to back in order to avoid special handling of items wrapping its end.

I haven't checked what the patch actually does, but it shouldn't have
any affect on MAP_FIXED or the new no-replace MAP_FIXED variant.

--Andy