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, 40 insertions, 0 deletions

diff --git a/arch/powerpc/sysdev/dcr.c b/arch/powerpc/sysdev/dcr.c
new file mode 100644
index 000000000..cb44a6995
--- /dev/null
+++ b/arch/powerpc/sysdev/dcr.c
@@ -0,0 +1,40 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ * (c) Copyright 2006 Benjamin Herrenschmidt, IBM Corp.
+ *                    <benh@kernel.crashing.org>
+ */
+
+#undef DEBUG
+
+#include <linux/kernel.h>
+#include <linux/export.h>
+#include <linux/of_address.h>
+#include <asm/dcr.h>
+
+unsigned int dcr_resource_start(const struct device_node *np,
+				unsigned int index)
+{
+	unsigned int ds;
+	const u32 *dr = of_get_property(np, "dcr-reg", &ds);
+
+	if (dr == NULL || ds & 1 || index >= (ds / 8))
+		return 0;
+
+	return dr[index * 2];
+}
+EXPORT_SYMBOL_GPL(dcr_resource_start);
+
+unsigned int dcr_resource_len(const struct device_node *np, unsigned int index)
+{
+	unsigned int ds;
+	const u32 *dr = of_get_property(np, "dcr-reg", &ds);
+
+	if (dr == NULL || ds & 1 || index >= (ds / 8))
+		return 0;
+
+	return dr[index * 2 + 1];
+}
+EXPORT_SYMBOL_GPL(dcr_resource_len);
+
+DEFINE_SPINLOCK(dcr_ind_lock);
+EXPORT_SYMBOL_GPL(dcr_ind_lock);