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, 46 insertions, 0 deletions

diff --git a/drivers/soc/microchip/mpfs-mss-top-sysreg.c b/drivers/soc/microchip/mpfs-mss-top-sysreg.c
new file mode 100644
index 000000000..b0f42b8dd
--- /dev/null
+++ b/drivers/soc/microchip/mpfs-mss-top-sysreg.c
@@ -0,0 +1,46 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <linux/array_size.h>
+#include <linux/of.h>
+#include <linux/mfd/core.h>
+#include <linux/mfd/syscon.h>
+#include <linux/of_platform.h>
+#include <linux/platform_device.h>
+
+static const struct mfd_cell mpfs_mss_top_sysreg_devs[] = {
+	MFD_CELL_NAME("mpfs-reset"),
+};
+
+static int mpfs_mss_top_sysreg_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	int ret;
+
+	ret = devm_mfd_add_devices(dev, PLATFORM_DEVID_NONE,
+				   mpfs_mss_top_sysreg_devs,
+				   ARRAY_SIZE(mpfs_mss_top_sysreg_devs), NULL,
+				   0, NULL);
+	if (ret)
+		return ret;
+
+	return devm_of_platform_populate(dev);
+}
+
+static const struct of_device_id mpfs_mss_top_sysreg_of_match[] = {
+	{ .compatible = "microchip,mpfs-mss-top-sysreg", },
+	{},
+};
+MODULE_DEVICE_TABLE(of, mpfs_mss_top_sysreg_of_match);
+
+static struct platform_driver mpfs_mss_top_sysreg_driver = {
+	.driver = {
+		.name = "mpfs-mss-top-sysreg",
+		.of_match_table = mpfs_mss_top_sysreg_of_match,
+	},
+	.probe = mpfs_mss_top_sysreg_probe,
+};
+module_platform_driver(mpfs_mss_top_sysreg_driver);
+
+MODULE_LICENSE("GPL");
+MODULE_AUTHOR("Conor Dooley <conor.dooley@microchip.com>");
+MODULE_DESCRIPTION("PolarFire SoC mss top sysreg driver");