[PATCH] drm/xe/guc_submit: add missing locking in wedged_fini

[Matthew Auld]

Any non-wedged queue can have a zero refcount here and can be running
concurrently with an async queue destroy, therefore dereferencing the
queue ptr to check wedge status after the lookup can trigger UAF if
queue is not wedged.  Fix this by keeping the submission_state lock held
around the check to postpone the free and make the check safe, before
dropping again around the put() to avoid the deadlock.

Fixes: 8ed9aaae39f3 ("drm/xe: Force wedged state and block GT reset upon any GPU hang")
Signed-off-by: Matthew Auld <matthew.auld at intel.com>
Cc: Matthew Brost <matthew.brost at intel.com>
---
 drivers/gpu/drm/xe/xe_guc_submit.c | 10 ++++++++--
 1 file changed, 8 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/xe/xe_guc_submit.c b/drivers/gpu/drm/xe/xe_guc_submit.c
index fbbe6a487bbb..715c761dc7d6 100644
--- a/drivers/gpu/drm/xe/xe_guc_submit.c
+++ b/drivers/gpu/drm/xe/xe_guc_submit.c
@@ -290,9 +290,15 @@ static void guc_submit_wedged_fini(void *arg)
 	struct xe_exec_queue *q;
 	unsigned long index;
 
-	xa_for_each(&guc->submission_state.exec_queue_lookup, index, q)
-		if (exec_queue_wedged(q))
+	mutex_lock(&guc->submission_state.lock);
+	xa_for_each(&guc->submission_state.exec_queue_lookup, index, q) {
+		if (exec_queue_wedged(q)) {
+			mutex_unlock(&guc->submission_state.lock);
 			xe_exec_queue_put(q);
+			mutex_lock(&guc->submission_state.lock);
+		}
+	}
+	mutex_unlock(&guc->submission_state.lock);
 }
 
 static const struct xe_exec_queue_ops guc_exec_queue_ops;
-- 
2.46.1