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

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Date:   Wed, 3 Oct 2018 23:21:44 +0200
From:   Eugene Syromiatnikov <esyr@...hat.com>
To:     Jann Horn <jannh@...gle.com>
Cc:     yu-cheng.yu@...el.com, Andy Lutomirski <luto@...capital.net>,
        the arch/x86 maintainers <x86@...nel.org>,
        "H . Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>,
        kernel list <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>, hjl.tools@...il.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>, rdunlap@...radead.org,
        ravi.v.shankar@...el.com, vedvyas.shanbhogue@...el.com
Subject: Re: [RFC PATCH v4 24/27] mm/mmap: Create a guard area between VMAs

On Wed, Oct 03, 2018 at 06:52:40PM +0200, Jann Horn wrote:
> On Wed, Oct 3, 2018 at 6:32 PM Eugene Syromiatnikov <esyr@...hat.com> wrote:
> > I'm not sure, however, whether such a change that provides no ability
> > to configure or affect it will go well with all the supported
> > architectures.
> 
> Is there a concrete reason why you think an architecture might not
> like this? As far as I can tell, the virtual address space overhead
> should be insignificant even for 32-bit systems.

Not really, and not architectures per se, but judging by some past
experiences with enabling ASLR, I would expect that all kinds of weird
applications may start to behave in all kinds of strange ways.

Not that I have anything more than this doubt, however; but this sort of
change without any ability to tune or revert it still looks unusual to me.