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

[Ketil Johnsen <ketil.johnsen@arm.com>]

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);
+}
+
 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);
 
-- 
2.43.0