From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 19BAAC77B75 for ; Wed, 19 Apr 2023 09:53:23 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232377AbjDSJxV (ORCPT ); Wed, 19 Apr 2023 05:53:21 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47936 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231783AbjDSJxS (ORCPT ); Wed, 19 Apr 2023 05:53:18 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 5062DE7 for ; Wed, 19 Apr 2023 02:53:17 -0700 (PDT) Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id A81B01063; Wed, 19 Apr 2023 02:54:00 -0700 (PDT) Received: from [10.57.20.93] (unknown [10.57.20.93]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id C10963F6C4; Wed, 19 Apr 2023 02:53:14 -0700 (PDT) Message-ID: Date: Wed, 19 Apr 2023 10:53:12 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.9.0 Subject: Re: [PATCH v2] drm/scheduler: set entity to NULL in drm_sched_entity_pop_job() Content-Language: en-GB To: Lucas Stach , Danilo Krummrich , luben.tuikov@amd.com, airlied@gmail.com, daniel@ffwll.ch, christian.koenig@amd.com Cc: linux-kernel@vger.kernel.org, dri-devel@lists.freedesktop.org References: <20230418100453.4433-1-dakr@redhat.com> <04f039ac71f3c0685a849b492478d18ec6ea4d11.camel@pengutronix.de> From: Steven Price In-Reply-To: <04f039ac71f3c0685a849b492478d18ec6ea4d11.camel@pengutronix.de> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 19/04/2023 10:44, Lucas Stach wrote: > Hi Steven, > > Am Mittwoch, dem 19.04.2023 um 10:39 +0100 schrieb Steven Price: >> On 18/04/2023 11:04, Danilo Krummrich wrote: >>> It already happend a few times that patches slipped through which >>> implemented access to an entity through a job that was already removed >>> from the entities queue. Since jobs and entities might have different >>> lifecycles, this can potentially cause UAF bugs. >>> >>> In order to make it obvious that a jobs entity pointer shouldn't be >>> accessed after drm_sched_entity_pop_job() was called successfully, set >>> the jobs entity pointer to NULL once the job is removed from the entity >>> queue. >>> >>> Moreover, debugging a potential NULL pointer dereference is way easier >>> than potentially corrupted memory through a UAF. >>> >>> Signed-off-by: Danilo Krummrich >> >> This triggers a splat for me (with Panfrost driver), the cause of which >> is the following code in drm_sched_get_cleanup_job(): >> >> if (job) { >> job->entity->elapsed_ns += ktime_to_ns( >> ktime_sub(job->s_fence->finished.timestamp, >> job->s_fence->scheduled.timestamp)); >> } >> >> which indeed is accessing entity after the job has been returned from >> drm_sched_entity_pop_job(). And obviously job->entity is a NULL pointer >> with this patch. >> >> I'm afraid I don't fully understand the lifecycle so I'm not sure if >> this is simply exposing an existing bug in drm_sched_get_cleanup_job() >> or if this commit needs to be reverted. >> > Not sure which tree you are on. The offending commit has been reverted > in 6.3-rc5. This is in drm-misc-next - I'm not sure which "offending commit" you are referring to. I'm referring to: 96c7c2f4d5bd ("drm/scheduler: set entity to NULL in drm_sched_entity_pop_job()") which was merged yesterday to drm-misc-next (and is currently the top commit). Is there another commit which has been reverted elsewhere which is conflicting? Steve > Regards, > Lucas > >> Thanks, >> >> Steve >> >>> --- >>> drivers/gpu/drm/scheduler/sched_entity.c | 6 ++++++ >>> drivers/gpu/drm/scheduler/sched_main.c | 4 ++++ >>> 2 files changed, 10 insertions(+) >>> >>> diff --git a/drivers/gpu/drm/scheduler/sched_entity.c b/drivers/gpu/drm/scheduler/sched_entity.c >>> index 15d04a0ec623..a9c6118e534b 100644 >>> --- a/drivers/gpu/drm/scheduler/sched_entity.c >>> +++ b/drivers/gpu/drm/scheduler/sched_entity.c >>> @@ -448,6 +448,12 @@ struct drm_sched_job *drm_sched_entity_pop_job(struct drm_sched_entity *entity) >>> drm_sched_rq_update_fifo(entity, next->submit_ts); >>> } >>> >>> + /* Jobs and entities might have different lifecycles. Since we're >>> + * removing the job from the entities queue, set the jobs entity pointer >>> + * to NULL to prevent any future access of the entity through this job. >>> + */ >>> + sched_job->entity = NULL; >>> + >>> return sched_job; >>> } >>> >>> diff --git a/drivers/gpu/drm/scheduler/sched_main.c b/drivers/gpu/drm/scheduler/sched_main.c >>> index 9b16480686f6..e89a3e469cd5 100644 >>> --- a/drivers/gpu/drm/scheduler/sched_main.c >>> +++ b/drivers/gpu/drm/scheduler/sched_main.c >>> @@ -42,6 +42,10 @@ >>> * the hardware. >>> * >>> * The jobs in a entity are always scheduled in the order that they were pushed. >>> + * >>> + * Note that once a job was taken from the entities queue and pushed to the >>> + * hardware, i.e. the pending queue, the entity must not be referenced anymore >>> + * through the jobs entity pointer. >>> */ >>> >>> #include >> >