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, 17 insertions, 0 deletions

diff --git a/scripts/Makefile.randstruct b/scripts/Makefile.randstruct
new file mode 100644
index 000000000..24e283e89
--- /dev/null
+++ b/scripts/Makefile.randstruct
@@ -0,0 +1,17 @@
+# SPDX-License-Identifier: GPL-2.0
+
+randstruct-cflags-y += -DRANDSTRUCT
+
+ifdef CONFIG_GCC_PLUGIN_RANDSTRUCT
+randstruct-cflags-y	\
+	+= -fplugin=$(objtree)/scripts/gcc-plugins/randomize_layout_plugin.so
+randstruct-cflags-$(CONFIG_RANDSTRUCT_PERFORMANCE)		\
+	+= -fplugin-arg-randomize_layout_plugin-performance-mode
+else
+randstruct-cflags-y	\
+	+= -frandomize-layout-seed-file=$(objtree)/scripts/basic/randstruct.seed
+endif
+
+export RANDSTRUCT_CFLAGS := $(randstruct-cflags-y)
+
+KBUILD_CFLAGS	+= $(RANDSTRUCT_CFLAGS)