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, 27 insertions, 0 deletions

diff --git a/rust/helpers/binder.c b/rust/helpers/binder.c
new file mode 100644
index 000000000..a2327f1b3
--- /dev/null
+++ b/rust/helpers/binder.c
@@ -0,0 +1,27 @@
+// SPDX-License-Identifier: GPL-2.0
+
+/*
+ * Copyright (C) 2025 Google LLC.
+ */
+
+#include <linux/list_lru.h>
+#include <linux/task_work.h>
+
+__rust_helper unsigned long rust_helper_list_lru_count(struct list_lru *lru)
+{
+	return list_lru_count(lru);
+}
+
+__rust_helper unsigned long rust_helper_list_lru_walk(struct list_lru *lru,
+						      list_lru_walk_cb isolate,
+						      void *cb_arg,
+						      unsigned long nr_to_walk)
+{
+	return list_lru_walk(lru, isolate, cb_arg, nr_to_walk);
+}
+
+__rust_helper void rust_helper_init_task_work(struct callback_head *twork,
+					      task_work_func_t func)
+{
+	init_task_work(twork, func);
+}