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, 29 insertions, 0 deletions

diff --git a/arch/mips/ralink/bootrom.c b/arch/mips/ralink/bootrom.c
new file mode 100644
index 000000000..8c8cc0a81
--- /dev/null
+++ b/arch/mips/ralink/bootrom.c
@@ -0,0 +1,29 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *
+ * Copyright (C) 2013 John Crispin <john@phrozen.org>
+ */
+
+#include <linux/debugfs.h>
+#include <linux/seq_file.h>
+
+#define BOOTROM_OFFSET	0x10118000
+#define BOOTROM_SIZE	0x8000
+
+static void __iomem *membase = (void __iomem *) KSEG1ADDR(BOOTROM_OFFSET);
+
+static int bootrom_show(struct seq_file *s, void *unused)
+{
+	seq_write(s, membase, BOOTROM_SIZE);
+
+	return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(bootrom);
+
+static int __init bootrom_setup(void)
+{
+	debugfs_create_file("bootrom", 0444, NULL, NULL, &bootrom_fops);
+	return 0;
+}
+
+postcore_initcall(bootrom_setup);