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, 19 insertions, 0 deletions

diff --git a/arch/powerpc/math-emu/fabs.c b/arch/powerpc/math-emu/fabs.c
new file mode 100644
index 000000000..3b62fd70b
--- /dev/null
+++ b/arch/powerpc/math-emu/fabs.c
@@ -0,0 +1,19 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/types.h>
+#include <linux/errno.h>
+#include <linux/uaccess.h>
+
+int
+fabs(u32 *frD, u32 *frB)
+{
+	frD[0] = frB[0] & 0x7fffffff;
+	frD[1] = frB[1];
+
+#ifdef DEBUG
+	printk("%s: D %p, B %p: ", __func__, frD, frB);
+	dump_double(frD);
+	printk("\n");
+#endif
+
+	return 0;
+}