From mboxrd@z Thu Jan 1 00:00:00 1970 From: Yu-cheng Yu Subject: Re: [RFC PATCH v4 24/27] mm/mmap: Create a guard area between VMAs Date: Wed, 03 Oct 2018 09:40:58 -0700 Message-ID: <36fa923c4ed6b78517b93475aa2544aa8ba7243c.camel@intel.com> References: <20180921150351.20898-1-yu-cheng.yu@intel.com> <20180921150351.20898-25-yu-cheng.yu@intel.com> <20181003045611.GB22724@asgard.redhat.com> <5ddb0ad33298d1858e530fce9c9ea2788b2fac81.camel@intel.com> <20181003163226.GC9449@asgard.redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20181003163226.GC9449@asgard.redhat.com> Sender: linux-kernel-owner@vger.kernel.org To: Eugene Syromiatnikov Cc: Andy Lutomirski , X86 ML , "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , LKML , linux-doc@vger.kernel.org, Linux-MM , linux-arch , Linux API , Arnd Bergmann , Balbir Singh , Cyrill Gorcunov , Dave Hansen , Florian Weimer , "H. J. Lu" , Jann Horn , Jonathan Corbet , Kees Cook , Mike Kravetz , Nadav Amit , Oleg List-Id: linux-arch.vger.kernel.org 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 > > > 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? From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mga11.intel.com ([192.55.52.93]:19275 "EHLO mga11.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726842AbeJCXfA (ORCPT ); Wed, 3 Oct 2018 19:35:00 -0400 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 Date: Wed, 03 Oct 2018 09:40:58 -0700 In-Reply-To: <20181003163226.GC9449@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> <5ddb0ad33298d1858e530fce9c9ea2788b2fac81.camel@intel.com> <20181003163226.GC9449@asgard.redhat.com> Content-Type: text/plain; charset="UTF-8" Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Sender: linux-arch-owner@vger.kernel.org List-ID: To: Eugene Syromiatnikov Cc: Andy Lutomirski , X86 ML , "H. Peter Anvin" , Thomas Gleixner , Ingo Molnar , LKML , linux-doc@vger.kernel.org, Linux-MM , linux-arch , Linux API , Arnd Bergmann , Balbir Singh , Cyrill Gorcunov , Dave Hansen , Florian Weimer , "H. J. Lu" , Jann Horn , Jonathan Corbet , Kees Cook , Mike Kravetz , Nadav Amit , Oleg Nesterov , Pavel Machek , Peter Zijlstra , Randy Dunlap , "Ravi V. Shankar" , "Shanbhogue, Vedvyas" Message-ID: <20181003164058.G3dgYhXFYgttvFx1Kyy5UOnA3y14p20vMQF5_-Yqpy0@z> 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 > > > 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?