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 CC572C77B75 for ; Wed, 19 Apr 2023 10:05:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232892AbjDSKFy (ORCPT ); Wed, 19 Apr 2023 06:05:54 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:59494 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232816AbjDSKFu (ORCPT ); Wed, 19 Apr 2023 06:05:50 -0400 Received: from foss.arm.com (foss.arm.com [217.140.110.172]) by lindbergh.monkeyblade.net (Postfix) with ESMTP id 5AE1EA5CE for ; Wed, 19 Apr 2023 03:05:49 -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 DA6BB106F; Wed, 19 Apr 2023 03:06:32 -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 777643F6C4; Wed, 19 Apr 2023 03:05:47 -0700 (PDT) Message-ID: <12a775f5-a4fe-6a61-c187-fb3afa0ab6e2@arm.com> Date: Wed, 19 Apr 2023 11:05:45 +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 From: Steven Price 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> In-Reply-To: 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 10:53, Steven Price wrote: > 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? Answering my own question, the conflicting commit is: baad10973fdb ("Revert "drm/scheduler: track GPU active time per entity"") But that commit isn't (yet) in drm-misc-next. Which unfortunately means drm-misc-next is broken until a back-merge happens. Steve