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, 21 insertions, 0 deletions

diff --git a/arch/powerpc/math-emu/stfd.c b/arch/powerpc/math-emu/stfd.c
new file mode 100644
index 000000000..463d2f083
--- /dev/null
+++ b/arch/powerpc/math-emu/stfd.c
@@ -0,0 +1,21 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/types.h>
+#include <linux/errno.h>
+#include <linux/uaccess.h>
+
+int
+stfd(void *frS, void *ea)
+{
+#if 0
+#ifdef DEBUG
+	printk("%s: S %p, ea %p: ", __func__, frS, ea);
+	dump_double(frS);
+	printk("\n");
+#endif
+#endif
+
+	if (copy_to_user(ea, frS, sizeof(double)))
+		return -EFAULT;
+
+	return 0;
+}