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, 32 insertions, 0 deletions

diff --git a/drivers/md/dm-vdo/thread-registry.h b/drivers/md/dm-vdo/thread-registry.h
new file mode 100644
index 000000000..cc6d78312
--- /dev/null
+++ b/drivers/md/dm-vdo/thread-registry.h
@@ -0,0 +1,32 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+/*
+ * Copyright 2023 Red Hat
+ */
+
+#ifndef VDO_THREAD_REGISTRY_H
+#define VDO_THREAD_REGISTRY_H
+
+#include <linux/list.h>
+#include <linux/spinlock.h>
+
+struct thread_registry {
+	struct list_head links;
+	spinlock_t lock;
+};
+
+struct registered_thread {
+	struct list_head links;
+	const void *pointer;
+	struct task_struct *task;
+};
+
+void vdo_initialize_thread_registry(struct thread_registry *registry);
+
+void vdo_register_thread(struct thread_registry *registry,
+			 struct registered_thread *new_thread, const void *pointer);
+
+void vdo_unregister_thread(struct thread_registry *registry);
+
+const void *vdo_lookup_thread(struct thread_registry *registry);
+
+#endif /* VDO_THREAD_REGISTRY_H */