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, 37 insertions, 0 deletions

diff --git a/include/uapi/asm-generic/ipcbuf.h b/include/uapi/asm-generic/ipcbuf.h
new file mode 100644
index 000000000..41a01b494
--- /dev/null
+++ b/include/uapi/asm-generic/ipcbuf.h
@@ -0,0 +1,37 @@
+/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
+#ifndef __ASM_GENERIC_IPCBUF_H
+#define __ASM_GENERIC_IPCBUF_H
+
+#include <linux/posix_types.h>
+
+/*
+ * The generic ipc64_perm structure:
+ * Note extra padding because this structure is passed back and forth
+ * between kernel and user space.
+ *
+ * ipc64_perm was originally meant to be architecture specific, but
+ * everyone just ended up making identical copies without specific
+ * optimizations, so we may just as well all use the same one.
+ *
+ * Pad space is left for:
+ * - 32-bit mode_t on architectures that only had 16 bit
+ * - 32-bit seq
+ * - 2 miscellaneous 32-bit values
+ */
+
+struct ipc64_perm {
+	__kernel_key_t		key;
+	__kernel_uid32_t	uid;
+	__kernel_gid32_t	gid;
+	__kernel_uid32_t	cuid;
+	__kernel_gid32_t	cgid;
+	__kernel_mode_t		mode;
+				/* pad if mode_t is u16: */
+	unsigned char		__pad1[4 - sizeof(__kernel_mode_t)];
+	unsigned short		seq;
+	unsigned short		__pad2;
+	__kernel_ulong_t	__unused1;
+	__kernel_ulong_t	__unused2;
+};
+
+#endif /* __ASM_GENERIC_IPCBUF_H */