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 <d...@redhat.com>
>
> 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.
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 <linux/kthread.h>
>
