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, 48 insertions, 0 deletions

diff --git a/arch/mips/sni/reset.c b/arch/mips/sni/reset.c
new file mode 100644
index 000000000..66f963d8d
--- /dev/null
+++ b/arch/mips/sni/reset.c
@@ -0,0 +1,48 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ *  linux/arch/mips/sni/process.c
+ *
+ *  Reset a SNI machine.
+ */
+#include <linux/delay.h>
+
+#include <asm/io.h>
+#include <asm/reboot.h>
+#include <asm/sni.h>
+
+/*
+ * This routine reboots the machine by asking the keyboard
+ * controller to pulse the reset-line low. We try that for a while,
+ * and if it doesn't work, we do some other stupid things.
+ */
+static inline void kb_wait(void)
+{
+	int i;
+
+	for (i = 0; i < 0x10000; i++)
+		if ((inb_p(0x64) & 0x02) == 0)
+			break;
+}
+
+/* XXX This ends up at the ARC firmware prompt ...  */
+void sni_machine_restart(char *command)
+{
+	int i;
+
+	/* This does a normal via the keyboard controller like a PC.
+	   We can do that easier ...  */
+	local_irq_disable();
+	for (;;) {
+		for (i = 0; i < 100; i++) {
+			kb_wait();
+			udelay(50);
+			outb_p(0xfe, 0x64);	 /* pulse reset low */
+			udelay(50);
+		}
+	}
+}
+
+void sni_machine_power_off(void)
+{
+	*(volatile unsigned char *)PCIMT_CSWCSM = 0xfd;
+}