From patchwork Thu Jun 12 22:25:09 2014 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Kamal Mostafa X-Patchwork-Id: 359362 Return-Path: X-Original-To: incoming@patchwork.ozlabs.org Delivered-To: patchwork-incoming@bilbo.ozlabs.org Received: from huckleberry.canonical.com (huckleberry.canonical.com [91.189.94.19]) by ozlabs.org (Postfix) with ESMTP id A820C14009E; Fri, 13 Jun 2014 08:26:33 +1000 (EST) Received: from localhost ([127.0.0.1] helo=huckleberry.canonical.com) by huckleberry.canonical.com with esmtp (Exim 4.76) (envelope-from ) id 1WvDS2-00058V-Qk; Thu, 12 Jun 2014 22:26:30 +0000 Received: from youngberry.canonical.com ([91.189.89.112]) by huckleberry.canonical.com with esmtp (Exim 4.76) (envelope-from ) id 1WvDQl-0004T7-NO for kernel-team@lists.ubuntu.com; Thu, 12 Jun 2014 22:25:11 +0000 Received: from c-67-160-228-185.hsd1.ca.comcast.net ([67.160.228.185] helo=fourier) by youngberry.canonical.com with esmtpsa (TLS1.0:DHE_RSA_AES_128_CBC_SHA1:16) (Exim 4.71) (envelope-from ) id 1WvDQl-0005up-7s; Thu, 12 Jun 2014 22:25:11 +0000 Received: from kamal by fourier with local (Exim 4.82) (envelope-from ) id 1WvDQj-0004ot-A4; Thu, 12 Jun 2014 15:25:09 -0700 From: Kamal Mostafa To: Mikulas Patocka Subject: [3.8.y.z extended stable] Patch "user namespace: fix incorrect memory barriers" has been added to staging queue Date: Thu, 12 Jun 2014 15:25:09 -0700 Message-Id: <1402611909-18496-1-git-send-email-kamal@canonical.com> X-Mailer: git-send-email 1.9.1 X-Extended-Stable: 3.8 Cc: Kamal Mostafa , Linus Torvalds , kernel-team@lists.ubuntu.com X-BeenThere: kernel-team@lists.ubuntu.com X-Mailman-Version: 2.1.14 Precedence: list List-Id: Kernel team discussions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , MIME-Version: 1.0 Errors-To: kernel-team-bounces@lists.ubuntu.com Sender: kernel-team-bounces@lists.ubuntu.com This is a note to let you know that I have just added a patch titled user namespace: fix incorrect memory barriers to the linux-3.8.y-queue branch of the 3.8.y.z extended stable tree which can be found at: http://kernel.ubuntu.com/git?p=ubuntu/linux.git;a=shortlog;h=refs/heads/linux-3.8.y-queue This patch is scheduled to be released in version 3.8.13.24. If you, or anyone else, feels it should not be added to this tree, please reply to this email. For more information about the 3.8.y.z tree, see https://wiki.ubuntu.com/Kernel/Dev/ExtendedStable Thanks. -Kamal ------ From 8b547dfc58e88ae7d2622f047a292dd309610f0b Mon Sep 17 00:00:00 2001 From: Mikulas Patocka Date: Mon, 14 Apr 2014 16:58:55 -0400 Subject: user namespace: fix incorrect memory barriers commit e79323bd87808fdfbc68ce6c5371bd224d9672ee upstream. smp_read_barrier_depends() can be used if there is data dependency between the readers - i.e. if the read operation after the barrier uses address that was obtained from the read operation before the barrier. In this file, there is only control dependency, no data dependecy, so the use of smp_read_barrier_depends() is incorrect. The code could fail in the following way: * the cpu predicts that idx < entries is true and starts executing the body of the for loop * the cpu fetches map->extent[0].first and map->extent[0].count * the cpu fetches map->nr_extents * the cpu verifies that idx < extents is true, so it commits the instructions in the body of the for loop The problem is that in this scenario, the cpu read map->extent[0].first and map->nr_extents in the wrong order. We need a full read memory barrier to prevent it. Signed-off-by: Mikulas Patocka Signed-off-by: Linus Torvalds Signed-off-by: Kamal Mostafa --- kernel/user_namespace.c | 11 +++++------ 1 file changed, 5 insertions(+), 6 deletions(-) -- 1.9.1 diff --git a/kernel/user_namespace.c b/kernel/user_namespace.c index b9b0b51..372211d 100644 --- a/kernel/user_namespace.c +++ b/kernel/user_namespace.c @@ -147,7 +147,7 @@ static u32 map_id_range_down(struct uid_gid_map *map, u32 id, u32 count) /* Find the matching extent */ extents = map->nr_extents; - smp_read_barrier_depends(); + smp_rmb(); for (idx = 0; idx < extents; idx++) { first = map->extent[idx].first; last = first + map->extent[idx].count - 1; @@ -171,7 +171,7 @@ static u32 map_id_down(struct uid_gid_map *map, u32 id) /* Find the matching extent */ extents = map->nr_extents; - smp_read_barrier_depends(); + smp_rmb(); for (idx = 0; idx < extents; idx++) { first = map->extent[idx].first; last = first + map->extent[idx].count - 1; @@ -194,7 +194,7 @@ static u32 map_id_up(struct uid_gid_map *map, u32 id) /* Find the matching extent */ extents = map->nr_extents; - smp_read_barrier_depends(); + smp_rmb(); for (idx = 0; idx < extents; idx++) { first = map->extent[idx].lower_first; last = first + map->extent[idx].count - 1; @@ -574,9 +574,8 @@ static ssize_t map_write(struct file *file, const char __user *buf, * were written before the count of the extents. * * To achieve this smp_wmb() is used on guarantee the write - * order and smp_read_barrier_depends() is guaranteed that we - * don't have crazy architectures returning stale data. - * + * order and smp_rmb() is guaranteed that we don't have crazy + * architectures returning stale data. */ mutex_lock(&id_map_mutex);