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Message-ID: <36fa923c4ed6b78517b93475aa2544aa8ba7243c.camel@intel.com>
Subject: Re: [RFC PATCH v4 24/27] mm/mmap: Create a guard area between VMAs
From: Yu-cheng Yu <yu-cheng.yu@intel.com>
Date: Wed, 03 Oct 2018 09:40:58 -0700
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To: Eugene Syromiatnikov <esyr@redhat.com>
Cc: Andy Lutomirski <luto@amacapital.net>, X86 ML <x86@kernel.org>, "H.
 Peter Anvin" <hpa@zytor.com>, Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>, LKML <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>, "H. J. Lu" <hjl.tools@gmail.com>, Jann Horn <jannh@google.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>, Randy Dunlap <rdunlap@infradead.org>, "Ravi V. Shankar" <ravi.v.shankar@intel.com>, "Shanbhogue, Vedvyas" <vedvyas.shanbhogue@intel.com>

On Wed, 2018-10-03 at 18:32 +0200, Eugene Syromiatnikov wrote:
> On Wed, Oct 03, 2018 at 09:00:04AM -0700, Yu-cheng Yu wrote:
> > On Tue, 2018-10-02 at 22:36 -0700, Andy Lutomirski wrote:
> > > On Tue, Oct 2, 2018 at 9:55 PM Eugene Syromiatnikov <esyr@redhat.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
> > 
> > I did some mmap tests with/without MAP_FIXED, and it works as intended.
> > In addition to the ring buffer, are there other test cases?
> 
> Right, after some more code reading I figured out that it indeed
> shouldn't affect MAP_FIXED, thank you for confirmation.
> 
> 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.

Can we do CONFIG_MMAP_GUARD_GAP?