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, 44 insertions, 0 deletions

diff --git a/drivers/video/videomode.c b/drivers/video/videomode.c
new file mode 100644
index 000000000..2ecf80c08
--- /dev/null
+++ b/drivers/video/videomode.c
@@ -0,0 +1,44 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * generic display timing functions
+ *
+ * Copyright (c) 2012 Steffen Trumtrar <s.trumtrar@pengutronix.de>, Pengutronix
+ */
+
+#include <linux/errno.h>
+#include <linux/export.h>
+#include <video/display_timing.h>
+#include <video/videomode.h>
+
+void videomode_from_timing(const struct display_timing *dt,
+			  struct videomode *vm)
+{
+	vm->pixelclock = dt->pixelclock.typ;
+	vm->hactive = dt->hactive.typ;
+	vm->hfront_porch = dt->hfront_porch.typ;
+	vm->hback_porch = dt->hback_porch.typ;
+	vm->hsync_len = dt->hsync_len.typ;
+
+	vm->vactive = dt->vactive.typ;
+	vm->vfront_porch = dt->vfront_porch.typ;
+	vm->vback_porch = dt->vback_porch.typ;
+	vm->vsync_len = dt->vsync_len.typ;
+
+	vm->flags = dt->flags;
+}
+EXPORT_SYMBOL_GPL(videomode_from_timing);
+
+int videomode_from_timings(const struct display_timings *disp,
+			  struct videomode *vm, unsigned int index)
+{
+	struct display_timing *dt;
+
+	dt = display_timings_get(disp, index);
+	if (!dt)
+		return -EINVAL;
+
+	videomode_from_timing(dt, vm);
+
+	return 0;
+}
+EXPORT_SYMBOL_GPL(videomode_from_timings);