Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
Date:   Wed, 3 Oct 2018 23:21:44 +0200
From:   Eugene Syromiatnikov <esyr@redhat.com>
To:     Jann Horn <jannh@google.com>
Cc:     yu-cheng.yu@intel.com, Andy Lutomirski <luto@amacapital.net>,
        the arch/x86 maintainers <x86@kernel.org>,
        "H . Peter Anvin" <hpa@zytor.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Ingo Molnar <mingo@redhat.com>,
        kernel list <linux-kernel@vger.kernel.org>,
        linux-doc@vger.kernel.org, Linux-MM <linux-mm@kvack.org>,
        linux-arch <linux-arch@vger.kernel.org>,
        Linux API <linux-api@vger.kernel.org>,
        Arnd Bergmann <arnd@arndb.de>,
        Balbir Singh <bsingharora@gmail.com>,
        Cyrill Gorcunov <gorcunov@gmail.com>,
        Dave Hansen <dave.hansen@linux.intel.com>,
        Florian Weimer <fweimer@redhat.com>, hjl.tools@gmail.com,
        Jonathan Corbet <corbet@lwn.net>,
        Kees Cook <keescook@chromium.org>,
        Mike Kravetz <mike.kravetz@oracle.com>,
        Nadav Amit <nadav.amit@gmail.com>,
        Oleg Nesterov <oleg@redhat.com>, Pavel Machek <pavel@ucw.cz>,
        Peter Zijlstra <peterz@infradead.org>, rdunlap@infradead.org,
        ravi.v.shankar@intel.com, vedvyas.shanbhogue@intel.com
Subject: Re: [RFC PATCH v4 24/27] mm/mmap: Create a guard area between VMAs
Message-ID: <20181003212029.GH32759@asgard.redhat.com>
References: <20180921150351.20898-1-yu-cheng.yu@intel.com>
 <20180921150351.20898-25-yu-cheng.yu@intel.com>
 <20181003045611.GB22724@asgard.redhat.com>
 <CALCETrU-Ny-uC1NqRedQwNKe2MMhsFEqZ08TtHJwbLfCACMmLw@mail.gmail.com>
 <5ddb0ad33298d1858e530fce9c9ea2788b2fac81.camel@intel.com>
 <20181003163226.GC9449@asgard.redhat.com>
 <CAG48ez0KZYv9BECMm0-BNypJ232jrdkFp6_4VYTA=WoB-8w89w@mail.gmail.com>
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <CAG48ez0KZYv9BECMm0-BNypJ232jrdkFp6_4VYTA=WoB-8w89w@mail.gmail.com>
User-Agent: Mutt/1.5.23 (2014-03-12)
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

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@redhat.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.