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, 98 insertions, 0 deletions

diff --git a/drivers/soc/atmel/sfr.c b/drivers/soc/atmel/sfr.c
new file mode 100644
index 000000000..cc94ca1b4
--- /dev/null
+++ b/drivers/soc/atmel/sfr.c
@@ -0,0 +1,98 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * sfr.c - driver for special function registers
+ *
+ * Copyright (C) 2019 Bootlin.
+ *
+ */
+#include <linux/mfd/syscon.h>
+#include <linux/module.h>
+#include <linux/nvmem-provider.h>
+#include <linux/random.h>
+#include <linux/of.h>
+#include <linux/platform_device.h>
+#include <linux/regmap.h>
+
+#define SFR_SN0		0x4c
+#define SFR_SN_SIZE	8
+
+struct atmel_sfr_priv {
+	struct regmap			*regmap;
+};
+
+static int atmel_sfr_read(void *context, unsigned int offset,
+			  void *buf, size_t bytes)
+{
+	struct atmel_sfr_priv *priv = context;
+
+	return regmap_bulk_read(priv->regmap, SFR_SN0 + offset,
+				buf, bytes / 4);
+}
+
+static struct nvmem_config atmel_sfr_nvmem_config = {
+	.name = "atmel-sfr",
+	.read_only = true,
+	.word_size = 4,
+	.stride = 4,
+	.size = SFR_SN_SIZE,
+	.reg_read = atmel_sfr_read,
+};
+
+static int atmel_sfr_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct device_node *np = dev->of_node;
+	struct nvmem_device *nvmem;
+	struct atmel_sfr_priv *priv;
+	u8 sn[SFR_SN_SIZE];
+	int ret;
+
+	priv = devm_kmalloc(dev, sizeof(*priv), GFP_KERNEL);
+	if (!priv)
+		return -ENOMEM;
+
+	priv->regmap = syscon_node_to_regmap(np);
+	if (IS_ERR(priv->regmap)) {
+		dev_err(dev, "cannot get parent's regmap\n");
+		return PTR_ERR(priv->regmap);
+	}
+
+	atmel_sfr_nvmem_config.dev = dev;
+	atmel_sfr_nvmem_config.priv = priv;
+
+	nvmem = devm_nvmem_register(dev, &atmel_sfr_nvmem_config);
+	if (IS_ERR(nvmem)) {
+		dev_err(dev, "error registering nvmem config\n");
+		return PTR_ERR(nvmem);
+	}
+
+	ret = atmel_sfr_read(priv, 0, sn, SFR_SN_SIZE);
+	if (ret == 0)
+		add_device_randomness(sn, SFR_SN_SIZE);
+
+	return ret;
+}
+
+static const struct of_device_id atmel_sfr_dt_ids[] = {
+	{
+		.compatible = "atmel,sama5d2-sfr",
+	}, {
+		.compatible = "atmel,sama5d4-sfr",
+	}, {
+		/* sentinel */
+	},
+};
+MODULE_DEVICE_TABLE(of, atmel_sfr_dt_ids);
+
+static struct platform_driver atmel_sfr_driver = {
+	.probe = atmel_sfr_probe,
+	.driver = {
+		.name = "atmel-sfr",
+		.of_match_table = atmel_sfr_dt_ids,
+	},
+};
+module_platform_driver(atmel_sfr_driver);
+
+MODULE_AUTHOR("Kamel Bouhara <kamel.bouhara@bootlin.com>");
+MODULE_DESCRIPTION("Atmel SFR SN driver for SAMA5D2/4 SoC family");
+MODULE_LICENSE("GPL v2");