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, 144 insertions, 0 deletions

diff --git a/drivers/nvmem/max77759-nvmem.c b/drivers/nvmem/max77759-nvmem.c
new file mode 100644
index 000000000..283000ec3
--- /dev/null
+++ b/drivers/nvmem/max77759-nvmem.c
@@ -0,0 +1,144 @@
+// SPDX-License-Identifier: GPL-2.0-only
+//
+// Copyright 2020 Google Inc
+// Copyright 2025 Linaro Ltd.
+//
+// NVMEM driver for Maxim MAX77759
+
+#include <linux/dev_printk.h>
+#include <linux/device.h>
+#include <linux/device/driver.h>
+#include <linux/err.h>
+#include <linux/mfd/max77759.h>
+#include <linux/module.h>
+#include <linux/nvmem-provider.h>
+#include <linux/overflow.h>
+#include <linux/platform_device.h>
+#include <linux/string.h>
+
+#define MAX77759_NVMEM_OPCODE_HEADER_LEN 3
+/*
+ * NVMEM commands have a three byte header (which becomes part of the command),
+ * so we need to subtract that.
+ */
+#define MAX77759_NVMEM_SIZE (MAX77759_MAXQ_OPCODE_MAXLENGTH \
+			     - MAX77759_NVMEM_OPCODE_HEADER_LEN)
+
+struct max77759_nvmem {
+	struct device *dev;
+	struct max77759 *max77759;
+};
+
+static int max77759_nvmem_reg_read(void *priv, unsigned int offset,
+				   void *val, size_t bytes)
+{
+	struct max77759_nvmem *nvmem = priv;
+	DEFINE_FLEX(struct max77759_maxq_command, cmd, cmd, length,
+		    MAX77759_NVMEM_OPCODE_HEADER_LEN);
+	DEFINE_FLEX(struct max77759_maxq_response, rsp, rsp, length,
+		    MAX77759_MAXQ_OPCODE_MAXLENGTH);
+	int ret;
+
+	cmd->cmd[0] = MAX77759_MAXQ_OPCODE_USER_SPACE_READ;
+	cmd->cmd[1] = offset;
+	cmd->cmd[2] = bytes;
+	rsp->length = bytes + MAX77759_NVMEM_OPCODE_HEADER_LEN;
+
+	ret = max77759_maxq_command(nvmem->max77759, cmd, rsp);
+	if (ret < 0)
+		return ret;
+
+	if (memcmp(cmd->cmd, rsp->rsp, MAX77759_NVMEM_OPCODE_HEADER_LEN)) {
+		dev_warn(nvmem->dev, "protocol error (read)\n");
+		return -EIO;
+	}
+
+	memcpy(val, &rsp->rsp[MAX77759_NVMEM_OPCODE_HEADER_LEN], bytes);
+
+	return 0;
+}
+
+static int max77759_nvmem_reg_write(void *priv, unsigned int offset,
+				    void *val, size_t bytes)
+{
+	struct max77759_nvmem *nvmem = priv;
+	DEFINE_FLEX(struct max77759_maxq_command, cmd, cmd, length,
+		    MAX77759_MAXQ_OPCODE_MAXLENGTH);
+	DEFINE_FLEX(struct max77759_maxq_response, rsp, rsp, length,
+		    MAX77759_MAXQ_OPCODE_MAXLENGTH);
+	int ret;
+
+	cmd->cmd[0] = MAX77759_MAXQ_OPCODE_USER_SPACE_WRITE;
+	cmd->cmd[1] = offset;
+	cmd->cmd[2] = bytes;
+	memcpy(&cmd->cmd[MAX77759_NVMEM_OPCODE_HEADER_LEN], val, bytes);
+	cmd->length = bytes + MAX77759_NVMEM_OPCODE_HEADER_LEN;
+	rsp->length = cmd->length;
+
+	ret = max77759_maxq_command(nvmem->max77759, cmd, rsp);
+	if (ret < 0)
+		return ret;
+
+	if (memcmp(cmd->cmd, rsp->rsp, cmd->length)) {
+		dev_warn(nvmem->dev, "protocol error (write)\n");
+		return -EIO;
+	}
+
+	return 0;
+}
+
+static int max77759_nvmem_probe(struct platform_device *pdev)
+{
+	struct nvmem_config config = {
+		.dev = &pdev->dev,
+		.name = dev_name(&pdev->dev),
+		.id = NVMEM_DEVID_NONE,
+		.type = NVMEM_TYPE_EEPROM,
+		.ignore_wp = true,
+		.size = MAX77759_NVMEM_SIZE,
+		.word_size = sizeof(u8),
+		.stride = sizeof(u8),
+		.reg_read = max77759_nvmem_reg_read,
+		.reg_write = max77759_nvmem_reg_write,
+	};
+	struct max77759_nvmem *nvmem;
+
+	nvmem = devm_kzalloc(&pdev->dev, sizeof(*nvmem), GFP_KERNEL);
+	if (!nvmem)
+		return -ENOMEM;
+
+	nvmem->dev = &pdev->dev;
+	nvmem->max77759 = dev_get_drvdata(pdev->dev.parent);
+
+	config.priv = nvmem;
+
+	return PTR_ERR_OR_ZERO(devm_nvmem_register(config.dev, &config));
+}
+
+static const struct of_device_id max77759_nvmem_of_id[] = {
+	{ .compatible = "maxim,max77759-nvmem", },
+	{ }
+};
+MODULE_DEVICE_TABLE(of, max77759_nvmem_of_id);
+
+static const struct platform_device_id max77759_nvmem_platform_id[] = {
+	{ "max77759-nvmem", },
+	{ }
+};
+MODULE_DEVICE_TABLE(platform, max77759_nvmem_platform_id);
+
+static struct platform_driver max77759_nvmem_driver = {
+	.driver = {
+		.name = "max77759-nvmem",
+		.probe_type = PROBE_PREFER_ASYNCHRONOUS,
+		.of_match_table = max77759_nvmem_of_id,
+	},
+	.probe = max77759_nvmem_probe,
+	.id_table = max77759_nvmem_platform_id,
+};
+
+module_platform_driver(max77759_nvmem_driver);
+
+MODULE_AUTHOR("André Draszik <andre.draszik@linaro.org>");
+MODULE_DESCRIPTION("NVMEM driver for Maxim MAX77759");
+MODULE_LICENSE("GPL");