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, 42 insertions, 0 deletions

diff --git a/init/noinitramfs.c b/init/noinitramfs.c
new file mode 100644
index 000000000..d1d26b93d
--- /dev/null
+++ b/init/noinitramfs.c
@@ -0,0 +1,42 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * init/noinitramfs.c
+ *
+ * Copyright (C) 2006, NXP Semiconductors, All Rights Reserved
+ * Author: Jean-Paul Saman <jean-paul.saman@nxp.com>
+ */
+#include <linux/init.h>
+#include <linux/stat.h>
+#include <linux/kdev_t.h>
+#include <linux/syscalls.h>
+#include <linux/init_syscalls.h>
+#include <linux/umh.h>
+
+/*
+ * Create a simple rootfs that is similar to the default initramfs
+ */
+static int __init default_rootfs(void)
+{
+	int err;
+
+	usermodehelper_enable();
+	err = init_mkdir("/dev", 0755);
+	if (err < 0)
+		goto out;
+
+	err = init_mknod("/dev/console", S_IFCHR | S_IRUSR | S_IWUSR,
+			new_encode_dev(MKDEV(5, 1)));
+	if (err < 0)
+		goto out;
+
+	err = init_mkdir("/root", 0700);
+	if (err < 0)
+		goto out;
+
+	return 0;
+
+out:
+	printk(KERN_WARNING "Failed to create a rootfs\n");
+	return err;
+}
+rootfs_initcall(default_rootfs);