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, 57 insertions, 0 deletions

diff --git a/arch/mips/jazz/reset.c b/arch/mips/jazz/reset.c
new file mode 100644
index 000000000..052b01f5d
--- /dev/null
+++ b/arch/mips/jazz/reset.c
@@ -0,0 +1,57 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Reset a Jazz machine.
+ *
+ * We don't trust the firmware so we do it the classic way by poking and
+ * stabbing at the keyboard controller ...
+ */
+#include <linux/jiffies.h>
+#include <asm/jazz.h>
+
+#define KBD_STAT_IBF		0x02	/* Keyboard input buffer full */
+
+static void jazz_write_output(unsigned char val)
+{
+	int status;
+
+	do {
+		status = jazz_kh->command;
+	} while (status & KBD_STAT_IBF);
+	jazz_kh->data = val;
+}
+
+static void jazz_write_command(unsigned char val)
+{
+	int status;
+
+	do {
+		status = jazz_kh->command;
+	} while (status & KBD_STAT_IBF);
+	jazz_kh->command = val;
+}
+
+static unsigned char jazz_read_status(void)
+{
+	return jazz_kh->command;
+}
+
+static inline void kb_wait(void)
+{
+	unsigned long start = jiffies;
+	unsigned long timeout = start + HZ/2;
+
+	do {
+		if (! (jazz_read_status() & 0x02))
+			return;
+	} while (time_before_eq(jiffies, timeout));
+}
+
+void jazz_machine_restart(char *command)
+{
+	while(1) {
+		kb_wait();
+		jazz_write_command(0xd1);
+		kb_wait();
+		jazz_write_output(0x00);
+	}
+}