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, 24 insertions, 0 deletions

diff --git a/arch/mips/generic/board-serval.its.S b/arch/mips/generic/board-serval.its.S
new file mode 100644
index 000000000..dde833efe
--- /dev/null
+++ b/arch/mips/generic/board-serval.its.S
@@ -0,0 +1,24 @@
+/* SPDX-License-Identifier: (GPL-2.0 OR MIT) */
+/ {
+	images {
+		fdt-serval_pcb105 {
+			description = "MSCC Serval PCB105 Device Tree";
+			data = /incbin/("boot/dts/mscc/serval_pcb105.dtb");
+			type = "flat_dt";
+			arch = "mips";
+			compression = "none";
+			hash {
+				algo = "sha1";
+			};
+		};
+	};
+
+	configurations {
+		pcb105 {
+			description = "Serval Linux kernel";
+			kernel = "kernel";
+			fdt = "fdt-serval_pcb105";
+			ramdisk = "ramdisk";
+		};
+	};
+};