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, 159 insertions, 0 deletions

diff --git a/drivers/video/console/dummycon.c b/drivers/video/console/dummycon.c
new file mode 100644
index 000000000..7d02470f1
--- /dev/null
+++ b/drivers/video/console/dummycon.c
@@ -0,0 +1,159 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ *  linux/drivers/video/dummycon.c -- A dummy console driver
+ *
+ *  To be used if there's no other console driver (e.g. for plain VGA text)
+ *  available, usually until fbcon takes console over.
+ */
+
+#include <linux/types.h>
+#include <linux/kdev_t.h>
+#include <linux/console.h>
+#include <linux/vt_kern.h>
+#include <linux/screen_info.h>
+#include <linux/init.h>
+#include <linux/module.h>
+
+/*
+ *  Dummy console driver
+ */
+
+#if defined(CONFIG_ARCH_FOOTBRIDGE) && defined(CONFIG_VGA_CONSOLE)
+#include <asm/vga.h>
+#define DUMMY_COLUMNS	vgacon_screen_info.orig_video_cols
+#define DUMMY_ROWS	vgacon_screen_info.orig_video_lines
+#else
+/* set by Kconfig. Use 80x25 for 640x480 and 160x64 for 1280x1024 */
+#define DUMMY_COLUMNS	CONFIG_DUMMY_CONSOLE_COLUMNS
+#define DUMMY_ROWS	CONFIG_DUMMY_CONSOLE_ROWS
+#endif
+
+#ifdef CONFIG_FRAMEBUFFER_CONSOLE_DEFERRED_TAKEOVER
+/* These are both protected by the console_lock */
+static RAW_NOTIFIER_HEAD(dummycon_output_nh);
+static bool dummycon_putc_called;
+
+void dummycon_register_output_notifier(struct notifier_block *nb)
+{
+	WARN_CONSOLE_UNLOCKED();
+
+	raw_notifier_chain_register(&dummycon_output_nh, nb);
+
+	if (dummycon_putc_called)
+		nb->notifier_call(nb, 0, NULL);
+}
+
+void dummycon_unregister_output_notifier(struct notifier_block *nb)
+{
+	WARN_CONSOLE_UNLOCKED();
+
+	raw_notifier_chain_unregister(&dummycon_output_nh, nb);
+}
+
+static void dummycon_putc(struct vc_data *vc, u16 c, unsigned int y,
+                          unsigned int x)
+{
+	WARN_CONSOLE_UNLOCKED();
+
+	dummycon_putc_called = true;
+	raw_notifier_call_chain(&dummycon_output_nh, 0, NULL);
+}
+
+static void dummycon_putcs(struct vc_data *vc, const u16 *s, unsigned int count,
+			   unsigned int ypos, unsigned int xpos)
+{
+	unsigned int i;
+
+	if (!dummycon_putc_called) {
+		/* Ignore erases */
+		for (i = 0 ; i < count; i++) {
+			if (s[i] != vc->vc_video_erase_char)
+				break;
+		}
+		if (i == count)
+			return;
+
+		dummycon_putc_called = true;
+	}
+
+	raw_notifier_call_chain(&dummycon_output_nh, 0, NULL);
+}
+
+static bool dummycon_blank(struct vc_data *vc, enum vesa_blank_mode blank,
+			   bool mode_switch)
+{
+	/* Redraw, so that we get putc(s) for output done while blanked */
+	return true;
+}
+
+static bool dummycon_switch(struct vc_data *vc)
+{
+	/*
+	 * Redraw, so that we get putc(s) for output done while switched
+	 * away. Informs deferred consoles to take over the display.
+	 */
+	return true;
+}
+#else
+static void dummycon_putc(struct vc_data *vc, u16 c, unsigned int y,
+			  unsigned int x) { }
+static void dummycon_putcs(struct vc_data *vc, const u16 *s, unsigned int count,
+			   unsigned int ypos, unsigned int xpos) { }
+static bool dummycon_blank(struct vc_data *vc, enum vesa_blank_mode blank,
+			   bool mode_switch)
+{
+	return false;
+}
+static bool dummycon_switch(struct vc_data *vc)
+{
+	return false;
+}
+#endif
+
+static const char *dummycon_startup(void)
+{
+    return "dummy device";
+}
+
+static void dummycon_init(struct vc_data *vc, bool init)
+{
+    vc->vc_can_do_color = 1;
+    if (init) {
+	vc->vc_cols = DUMMY_COLUMNS;
+	vc->vc_rows = DUMMY_ROWS;
+    } else
+	vc_resize(vc, DUMMY_COLUMNS, DUMMY_ROWS);
+}
+
+static void dummycon_deinit(struct vc_data *vc) { }
+static void dummycon_clear(struct vc_data *vc, unsigned int sy, unsigned int sx,
+			   unsigned int width) { }
+static void dummycon_cursor(struct vc_data *vc, bool enable) { }
+
+static bool dummycon_scroll(struct vc_data *vc, unsigned int top,
+			    unsigned int bottom, enum con_scroll dir,
+			    unsigned int lines)
+{
+	return false;
+}
+
+/*
+ *  The console `switch' structure for the dummy console
+ *
+ *  Most of the operations are dummies.
+ */
+
+const struct consw dummy_con = {
+	.owner =		THIS_MODULE,
+	.con_startup =	dummycon_startup,
+	.con_init =		dummycon_init,
+	.con_deinit =	dummycon_deinit,
+	.con_clear =	dummycon_clear,
+	.con_putc =		dummycon_putc,
+	.con_putcs =	dummycon_putcs,
+	.con_cursor =	dummycon_cursor,
+	.con_scroll =	dummycon_scroll,
+	.con_switch =	dummycon_switch,
+	.con_blank =	dummycon_blank,
+};
+EXPORT_SYMBOL_GPL(dummy_con);