releases/6.10.8/drm-xe-prevent-uaf-around-preempt-fence.patch

From e59cf8c139edce087792a08b37ec50bc5da56e47 Mon Sep 17 00:00:00 2001
From: Sasha Levin <sashal@kernel.org>
Date: Wed, 14 Aug 2024 12:01:30 +0100
Subject: drm/xe: prevent UAF around preempt fence

From: Matthew Auld <matthew.auld@intel.com>

[ Upstream commit 730b72480e29f63fd644f5fa57c9d46109428953 ]

The fence lock is part of the queue, therefore in the current design
anything locking the fence should then also hold a ref to the queue to
prevent the queue from being freed.

However, currently it looks like we signal the fence and then drop the
queue ref, but if something is waiting on the fence, the waiter is
kicked to wake up at some later point, where upon waking up it first
grabs the lock before checking the fence state. But if we have already
dropped the queue ref, then the lock might already be freed as part of
the queue, leading to uaf.

To prevent this, move the fence lock into the fence itself so we don't
run into lifetime issues. Alternative might be to have device level
lock, or only release the queue in the fence release callback, however
that might require pushing to another worker to avoid locking issues.

Fixes: dd08ebf6c352 ("drm/xe: Introduce a new DRM driver for Intel GPUs")
References: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/2454
References: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/2342
References: https://gitlab.freedesktop.org/drm/xe/kernel/-/issues/2020
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Cc: Matthew Brost <matthew.brost@intel.com>
Cc: <stable@vger.kernel.org> # v6.8+
Reviewed-by: Matthew Brost <matthew.brost@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240814110129.825847-2-matthew.auld@intel.com
(cherry picked from commit 7116c35aacedc38be6d15bd21b2fc936eed0008b)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
 drivers/gpu/drm/xe/xe_exec_queue.c          | 1 -
 drivers/gpu/drm/xe/xe_exec_queue_types.h    | 2 --
 drivers/gpu/drm/xe/xe_preempt_fence.c       | 3 ++-
 drivers/gpu/drm/xe/xe_preempt_fence_types.h | 2 ++
 4 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/xe/xe_exec_queue.c b/drivers/gpu/drm/xe/xe_exec_queue.c
index 316731c5cce6d..ba7013f82c8b6 100644
--- a/drivers/gpu/drm/xe/xe_exec_queue.c
+++ b/drivers/gpu/drm/xe/xe_exec_queue.c
@@ -632,7 +632,6 @@ int xe_exec_queue_create_ioctl(struct drm_device *dev, void *data,
 
 		if (xe_vm_in_preempt_fence_mode(vm)) {
 			q->lr.context = dma_fence_context_alloc(1);
-			spin_lock_init(&q->lr.lock);
 
 			err = xe_vm_add_compute_exec_queue(vm, q);
 			if (XE_IOCTL_DBG(xe, err))
diff --git a/drivers/gpu/drm/xe/xe_exec_queue_types.h b/drivers/gpu/drm/xe/xe_exec_queue_types.h
index 52a1965d91375..a5aa43942d8cf 100644
--- a/drivers/gpu/drm/xe/xe_exec_queue_types.h
+++ b/drivers/gpu/drm/xe/xe_exec_queue_types.h
@@ -125,8 +125,6 @@ struct xe_exec_queue {
 		u32 seqno;
 		/** @lr.link: link into VM's list of exec queues */
 		struct list_head link;
-		/** @lr.lock: preemption fences lock */
-		spinlock_t lock;
 	} lr;
 
 	/** @ops: submission backend exec queue operations */
diff --git a/drivers/gpu/drm/xe/xe_preempt_fence.c b/drivers/gpu/drm/xe/xe_preempt_fence.c
index e8b8ae5c6485e..c453f45328b1c 100644
--- a/drivers/gpu/drm/xe/xe_preempt_fence.c
+++ b/drivers/gpu/drm/xe/xe_preempt_fence.c
@@ -128,8 +128,9 @@ xe_preempt_fence_arm(struct xe_preempt_fence *pfence, struct xe_exec_queue *q,
 {
 	list_del_init(&pfence->link);
 	pfence->q = xe_exec_queue_get(q);
+	spin_lock_init(&pfence->lock);
 	dma_fence_init(&pfence->base, &preempt_fence_ops,
-		      &q->lr.lock, context, seqno);
+		      &pfence->lock, context, seqno);
 
 	return &pfence->base;
 }
diff --git a/drivers/gpu/drm/xe/xe_preempt_fence_types.h b/drivers/gpu/drm/xe/xe_preempt_fence_types.h
index b54b5c29b5331..312c3372a49f9 100644
--- a/drivers/gpu/drm/xe/xe_preempt_fence_types.h
+++ b/drivers/gpu/drm/xe/xe_preempt_fence_types.h
@@ -25,6 +25,8 @@ struct xe_preempt_fence {
 	struct xe_exec_queue *q;
 	/** @preempt_work: work struct which issues preemption */
 	struct work_struct preempt_work;
+	/** @lock: dma-fence fence lock */
+	spinlock_t lock;
 	/** @error: preempt fence is in error state */
 	int error;
 };
-- 
2.43.0