Re: [PATCH] drm/panthor: Fix UAF race between device unplug and FW event processing

[Boris Brezillon <boris.brezillon@collabora.com>]

On Wed,  8 Oct 2025 12:53:20 +0200
Ketil Johnsen <ketil.johnsen@arm.com> wrote:

> The function panthor_fw_unplug() will free the FW memory sections.
> The problem is that there could still be pending FW events which are yet
> not handled at this point. process_fw_events_work() can in this case try
> to access said freed memory.
> 
> The fix is to stop FW event processing after IRQs are disabled but before
> the FW memory is freed.
> 
> Signed-off-by: Ketil Johnsen <ketil.johnsen@arm.com>
> ---
>  drivers/gpu/drm/panthor/panthor_fw.c    |  3 +++
>  drivers/gpu/drm/panthor/panthor_sched.c | 12 ++++++++++++
>  drivers/gpu/drm/panthor/panthor_sched.h |  1 +
>  3 files changed, 16 insertions(+)
> 
> diff --git a/drivers/gpu/drm/panthor/panthor_fw.c b/drivers/gpu/drm/panthor/panthor_fw.c
> index 9bf06e55eaee..4f393c5cd26f 100644
> --- a/drivers/gpu/drm/panthor/panthor_fw.c
> +++ b/drivers/gpu/drm/panthor/panthor_fw.c
> @@ -1172,6 +1172,9 @@ void panthor_fw_unplug(struct panthor_device *ptdev)
>  		panthor_fw_stop(ptdev);
>  	}
>  
> +	/* Any pending FW event processing must stop before we free FW memory */
> +	panthor_sched_stop_fw_events(ptdev);
> +
>  	list_for_each_entry(section, &ptdev->fw->sections, node)
>  		panthor_kernel_bo_destroy(section->mem);
>  
> diff --git a/drivers/gpu/drm/panthor/panthor_sched.c b/drivers/gpu/drm/panthor/panthor_sched.c
> index 0cc9055f4ee5..d150c8d99432 100644
> --- a/drivers/gpu/drm/panthor/panthor_sched.c
> +++ b/drivers/gpu/drm/panthor/panthor_sched.c
> @@ -1794,6 +1794,18 @@ void panthor_sched_report_fw_events(struct panthor_device *ptdev, u32 events)
>  	sched_queue_work(ptdev->scheduler, fw_events);
>  }
>  
> +/**
> + * panthor_sched_stop_fw_events() - Stop processing FW events.
> + */
> +void panthor_sched_stop_fw_events(struct panthor_device *ptdev)
> +{
> +	if (!ptdev->scheduler)
> +		return;
> +
> +	atomic_set(&ptdev->scheduler->fw_events, 0);
> +	cancel_work_sync(&ptdev->scheduler->fw_events_work);
> +}

Hm, I'd rather have this called from sched_unplug() and then have an
extra check in panthor_sched_report_fw_events() to bail out if the
scheduler component is no longer functional. This way this helper stays
private to panthor_sched.c.

> +
>  static const char *fence_get_driver_name(struct dma_fence *fence)
>  {
>  	return "panthor";
> diff --git a/drivers/gpu/drm/panthor/panthor_sched.h b/drivers/gpu/drm/panthor/panthor_sched.h
> index f4a475aa34c0..4393599ed330 100644
> --- a/drivers/gpu/drm/panthor/panthor_sched.h
> +++ b/drivers/gpu/drm/panthor/panthor_sched.h
> @@ -51,6 +51,7 @@ void panthor_sched_resume(struct panthor_device *ptdev);
>  
>  void panthor_sched_report_mmu_fault(struct panthor_device *ptdev);
>  void panthor_sched_report_fw_events(struct panthor_device *ptdev, u32 events);
> +void panthor_sched_stop_fw_events(struct panthor_device *ptdev);
>  
>  void panthor_fdinfo_gather_group_samples(struct panthor_file *pfile);
>