selftests/bpf: Reject graph kptr use after RCU unlockgrafted

Add a sleepable verifier test that loads a graph-node local kptr in an
explicit RCU read-side critical section, then passes its node to
bpf_rbtree_remove() after the section ends.

Before the verifier fix, the stale NON_OWN_REF flag makes the node look like
a live borrowed reference and the program is accepted. After the fix, the
pointer is demoted without NON_OWN_REF and the graph kfunc argument is
rejected.

Also exercise a graph kptr loaded while a spin lock provides implicit RCU
protection. The pointer must be invalidated when the lock is released, which
guards the required ordering between non-owning-reference invalidation and
RCU demotion.

Update the existing fault-protected load test state description. The
post-unlock pointer no longer carries NON_OWN_REF, but remains readable
because the load is rewritten to use BPF_PROBE_MEM.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20260904084325.52250-7-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

1 files changed, 136 insertions, 0 deletions

diff --git a/include/drm/drm_syncobj.h b/include/drm/drm_syncobj.h
new file mode 100644
index 000000000..b40052132
--- /dev/null
+++ b/include/drm/drm_syncobj.h
@@ -0,0 +1,136 @@
+/*
+ * Copyright © 2017 Red Hat
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice (including the next
+ * paragraph) shall be included in all copies or substantial portions of the
+ * Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
+ * FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS
+ * IN THE SOFTWARE.
+ *
+ * Authors:
+ *
+ */
+#ifndef __DRM_SYNCOBJ_H__
+#define __DRM_SYNCOBJ_H__
+
+#include <linux/dma-fence.h>
+#include <linux/dma-fence-chain.h>
+
+struct drm_file;
+
+/**
+ * struct drm_syncobj - sync object.
+ *
+ * This structure defines a generic sync object which wraps a &dma_fence.
+ */
+struct drm_syncobj {
+	/**
+	 * @refcount: Reference count of this object.
+	 */
+	struct kref refcount;
+	/**
+	 * @fence:
+	 * NULL or a pointer to the fence bound to this object.
+	 *
+	 * This field should not be used directly. Use drm_syncobj_fence_get()
+	 * and drm_syncobj_replace_fence() instead.
+	 */
+	struct dma_fence __rcu *fence;
+	/**
+	 * @cb_list: List of callbacks to call when the &fence gets replaced.
+	 */
+	struct list_head cb_list;
+	/**
+	 * @ev_fd_list: List of registered eventfd.
+	 */
+	struct list_head ev_fd_list;
+	/**
+	 * @lock: Protects &cb_list and &ev_fd_list, and write-locks &fence.
+	 */
+	spinlock_t lock;
+	/**
+	 * @file: A file backing for this syncobj.
+	 */
+	struct file *file;
+};
+
+void drm_syncobj_free(struct kref *kref);
+
+/**
+ * drm_syncobj_get - acquire a syncobj reference
+ * @obj: sync object
+ *
+ * This acquires an additional reference to @obj. It is illegal to call this
+ * without already holding a reference. No locks required.
+ */
+static inline void
+drm_syncobj_get(struct drm_syncobj *obj)
+{
+	kref_get(&obj->refcount);
+}
+
+/**
+ * drm_syncobj_put - release a reference to a sync object.
+ * @obj: sync object.
+ */
+static inline void
+drm_syncobj_put(struct drm_syncobj *obj)
+{
+	kref_put(&obj->refcount, drm_syncobj_free);
+}
+
+/**
+ * drm_syncobj_fence_get - get a reference to a fence in a sync object
+ * @syncobj: sync object.
+ *
+ * This acquires additional reference to &drm_syncobj.fence contained in @obj,
+ * if not NULL. It is illegal to call this without already holding a reference.
+ * No locks required.
+ *
+ * Returns:
+ * Either the fence of @obj or NULL if there's none.
+ */
+static inline struct dma_fence *
+drm_syncobj_fence_get(struct drm_syncobj *syncobj)
+{
+	struct dma_fence *fence;
+
+	rcu_read_lock();
+	fence = dma_fence_get_rcu_safe(&syncobj->fence);
+	rcu_read_unlock();
+
+	return fence;
+}
+
+struct drm_syncobj *drm_syncobj_find(struct drm_file *file_private,
+				     u32 handle);
+void drm_syncobj_add_point(struct drm_syncobj *syncobj,
+			   struct dma_fence_chain *chain,
+			   struct dma_fence *fence,
+			   uint64_t point);
+void drm_syncobj_replace_fence(struct drm_syncobj *syncobj,
+			       struct dma_fence *fence);
+int drm_syncobj_find_fence(struct drm_file *file_private,
+			   u32 handle, u64 point, u64 flags,
+			   struct dma_fence **fence);
+void drm_syncobj_free(struct kref *kref);
+int drm_syncobj_create(struct drm_syncobj **out_syncobj, uint32_t flags,
+		       struct dma_fence *fence);
+int drm_syncobj_get_handle(struct drm_file *file_private,
+			   struct drm_syncobj *syncobj, u32 *handle);
+int drm_syncobj_get_fd(struct drm_syncobj *syncobj, int *p_fd);
+
+#endif