[PATCH v2 5/6] nvmem: rmem: add CRC validation for Mobileye EyeQ5 NVMEM

[Théo Lebrun <theo.lebrun@xxxxxxxxxxx>]

Mobileye EyeQ5 has a non-volatile memory region which
gets used to store MAC addresses. Its format includes
a prefix 12-byte header and a suffix 4-byte CRC.

Add an optional ->checksum() callback inside match data;
it runs CRC32 onto the content.

Signed-off-by: Théo Lebrun <theo.lebrun@xxxxxxxxxxx>
---
 drivers/nvmem/rmem.c | 81 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 81 insertions(+)

diff --git a/drivers/nvmem/rmem.c b/drivers/nvmem/rmem.c
index ca89c2689031534ff316a48e03360aeec823b025..1f0caf1d2dc1b3d42e5ac79b55222beb59fdd30d 100644
--- a/drivers/nvmem/rmem.c
+++ b/drivers/nvmem/rmem.c
@@ -3,11 +3,13 @@
  * Copyright (C) 2020 Nicolas Saenz Julienne <nsaenzjulienne@xxxxxxx>
  */
 
+#include <linux/crc32.h>
 #include <linux/io.h>
 #include <linux/module.h>
 #include <linux/nvmem-provider.h>
 #include <linux/of_reserved_mem.h>
 #include <linux/platform_device.h>
+#include <linux/slab.h>
 
 struct rmem {
 	struct device *dev;
@@ -15,6 +17,18 @@ struct rmem {
 	struct reserved_mem *mem;
 };
 
+struct rmem_match_data {
+	int (*checksum)(struct rmem *priv);
+};
+
+struct __packed rmem_eyeq5_header {
+	u32 magic;
+	u32 version;
+	u32 size;
+};
+
+#define RMEM_EYEQ5_MAGIC	((u32)0xDABBAD00)
+
 static int rmem_read(void *context, unsigned int offset,
 		     void *val, size_t bytes)
 {
@@ -47,10 +61,66 @@ static int rmem_read(void *context, unsigned int offset,
 	return 0;
 }
 
+static int rmem_eyeq5_checksum(struct rmem *priv)
+{
+	struct rmem_eyeq5_header header;
+	void *buf __free(kfree) = NULL;
+	u32 computed_crc, *target_crc;
+	size_t data_size;
+	int ret;
+
+	ret = rmem_read(priv, 0, &header, sizeof(header));
+	if (ret)
+		return ret;
+
+	if (header.magic != RMEM_EYEQ5_MAGIC)
+		return -EINVAL;
+
+	/*
+	 * Avoid massive kmalloc() if header read is invalid;
+	 * the check would be done by the next rmem_read() anyway.
+	 */
+	if (header.size > priv->mem->size)
+		return -EINVAL;
+
+	/*
+	 *           0 +-------------------+
+	 *             | Header (12 bytes) | \
+	 *             +-------------------+ |
+	 *             |                   | | data to be CRCed
+	 *             |        ...        | |
+	 *             |                   | /
+	 *   data_size +-------------------+
+	 *             |   CRC (4 bytes)   |
+	 * header.size +-------------------+
+	 */
+
+	buf = kmalloc(header.size, GFP_KERNEL);
+	if (!buf)
+		return -ENOMEM;
+
+	ret = rmem_read(priv, 0, buf, header.size);
+	if (ret)
+		return ret;
+
+	data_size = header.size - sizeof(*target_crc);
+	target_crc = buf + data_size;
+	computed_crc = crc32(U32_MAX, buf, data_size) ^ U32_MAX;
+
+	if (computed_crc == *target_crc)
+		return 0;
+
+	dev_err(priv->dev,
+		"checksum failed: computed %#x, expected %#x, header (%#x, %#x, %#x)\n",
+		computed_crc, *target_crc, header.magic, header.version, header.size);
+	return -EINVAL;
+}
+
 static int rmem_probe(struct platform_device *pdev)
 {
 	struct nvmem_config config = { };
 	struct device *dev = &pdev->dev;
+	const struct rmem_match_data *match_data = device_get_match_data(dev);
 	struct reserved_mem *mem;
 	struct rmem *priv;
 
@@ -73,10 +143,21 @@ static int rmem_probe(struct platform_device *pdev)
 	config.size = mem->size;
 	config.reg_read = rmem_read;
 
+	if (match_data && match_data->checksum) {
+		int ret = match_data->checksum(priv);
+		if (ret)
+			return ret;
+	}
+
 	return PTR_ERR_OR_ZERO(devm_nvmem_register(dev, &config));
 }
 
+static const struct rmem_match_data rmem_eyeq5_match_data = {
+	.checksum = rmem_eyeq5_checksum,
+};
+
 static const struct of_device_id rmem_match[] = {
+	{ .compatible = "mobileye,eyeq5-bootloader-config", .data = &rmem_eyeq5_match_data },
 	{ .compatible = "nvmem-rmem", },
 	{ /* sentinel */ },
 };

-- 
2.47.1