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, 24 insertions, 0 deletions

diff --git a/drivers/base/hypervisor.c b/drivers/base/hypervisor.c
new file mode 100644
index 000000000..1ce59b4b5
--- /dev/null
+++ b/drivers/base/hypervisor.c
@@ -0,0 +1,24 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * hypervisor.c - /sys/hypervisor subsystem.
+ *
+ * Copyright (C) IBM Corp. 2006
+ * Copyright (C) 2007 Greg Kroah-Hartman <gregkh@suse.de>
+ * Copyright (C) 2007 Novell Inc.
+ */
+
+#include <linux/kobject.h>
+#include <linux/device.h>
+#include <linux/export.h>
+#include "base.h"
+
+struct kobject *hypervisor_kobj;
+EXPORT_SYMBOL_GPL(hypervisor_kobj);
+
+int __init hypervisor_init(void)
+{
+	hypervisor_kobj = kobject_create_and_add("hypervisor", NULL);
+	if (!hypervisor_kobj)
+		return -ENOMEM;
+	return 0;
+}