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Date: Wed, 3 Oct 2018 23:21:44 +0200
From: Eugene Syromiatnikov <esyr@redhat.com>
Subject: Re: [RFC PATCH v4 24/27] mm/mmap: Create a guard area between VMAs
Message-ID: <20181003212029.GH32759@asgard.redhat.com>
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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

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.