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, 73 insertions, 0 deletions

diff --git a/arch/mips/cobalt/serial.c b/arch/mips/cobalt/serial.c
new file mode 100644
index 000000000..5fb676719
--- /dev/null
+++ b/arch/mips/cobalt/serial.c
@@ -0,0 +1,73 @@
+// SPDX-License-Identifier: GPL-2.0-or-later
+/*
+ *  Registration of Cobalt UART platform device.
+ *
+ *  Copyright (C) 2007  Yoichi Yuasa <yuasa@linux-mips.org>
+ */
+#include <linux/errno.h>
+#include <linux/init.h>
+#include <linux/ioport.h>
+#include <linux/platform_device.h>
+#include <linux/serial_8250.h>
+
+#include <cobalt.h>
+#include <irq.h>
+
+static struct resource cobalt_uart_resource[] __initdata = {
+	{
+		.start	= 0x1c800000,
+		.end	= 0x1c800007,
+		.flags	= IORESOURCE_MEM,
+	},
+	{
+		.start	= SERIAL_IRQ,
+		.end	= SERIAL_IRQ,
+		.flags	= IORESOURCE_IRQ,
+	},
+};
+
+static struct plat_serial8250_port cobalt_serial8250_port[] = {
+	{
+		.irq		= SERIAL_IRQ,
+		.uartclk	= 18432000,
+		.iotype		= UPIO_MEM,
+		.flags		= UPF_IOREMAP | UPF_BOOT_AUTOCONF | UPF_SKIP_TEST,
+		.mapbase	= 0x1c800000,
+	},
+	{},
+};
+
+static __init int cobalt_uart_add(void)
+{
+	struct platform_device *pdev;
+	int retval;
+
+	/*
+	 * Cobalt Qube1 has no UART.
+	 */
+	if (cobalt_board_id == COBALT_BRD_ID_QUBE1)
+		return 0;
+
+	pdev = platform_device_alloc("serial8250", -1);
+	if (!pdev)
+		return -ENOMEM;
+
+	pdev->id = PLAT8250_DEV_PLATFORM;
+	pdev->dev.platform_data = cobalt_serial8250_port;
+
+	retval = platform_device_add_resources(pdev, cobalt_uart_resource, ARRAY_SIZE(cobalt_uart_resource));
+	if (retval)
+		goto err_free_device;
+
+	retval = platform_device_add(pdev);
+	if (retval)
+		goto err_free_device;
+
+	return 0;
+
+err_free_device:
+	platform_device_put(pdev);
+
+	return retval;
+}
+device_initcall(cobalt_uart_add);