[PATCH 1/2] eeprom: at24: Add support for the Sony VAIO EEPROMs

[Jean Delvare <jdelvare@suse.de>]

Special handling of the Sony VAIO EEPROMs is the last feature of the
legacy eeprom driver that the at24 driver does not support. Adding
this would let us deprecate and eventually remove the legacy eeprom
driver.

So add the option to specify a post-processing callback function that
is called after reading data from the EEPROM, before it is returned
to the user. The 24c02-vaio type is the first use case of that option:
the callback function will mask the sensitive data for non-root users
exactly as the legacy eeprom driver was doing.

Signed-off-by: Jean Delvare <jdelvare@suse.de>
Cc: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
Bartosz, this is a different approach to solving the problem compared
to your suggestion. It's even more generic in a way. Let me know what
you think.

 drivers/misc/eeprom/at24.c |   42 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 42 insertions(+)

--- linux-5.7.orig/drivers/misc/eeprom/at24.c	2020-06-01 01:49:15.000000000 +0200
+++ linux-5.7/drivers/misc/eeprom/at24.c	2020-08-07 12:46:47.075238130 +0200
@@ -8,6 +8,7 @@
 
 #include <linux/acpi.h>
 #include <linux/bitops.h>
+#include <linux/capability.h>
 #include <linux/delay.h>
 #include <linux/i2c.h>
 #include <linux/init.h>
@@ -89,6 +90,7 @@ struct at24_data {
 
 	struct nvmem_device *nvmem;
 	struct regulator *vcc_reg;
+	void (*read_post)(unsigned int off, char *buf, size_t count);
 
 	/*
 	 * Some chips tie up multiple I2C addresses; dummy devices reserve
@@ -121,6 +123,7 @@ MODULE_PARM_DESC(at24_write_timeout, "Ti
 struct at24_chip_data {
 	u32 byte_len;
 	u8 flags;
+	void (*read_post)(unsigned int off, char *buf, size_t count);
 };
 
 #define AT24_CHIP_DATA(_name, _len, _flags)				\
@@ -128,6 +131,33 @@ struct at24_chip_data {
 		.byte_len = _len, .flags = _flags,			\
 	}
 
+#define AT24_CHIP_DATA_CB(_name, _len, _flags, _read_post)		\
+	static const struct at24_chip_data _name = {			\
+		.byte_len = _len, .flags = _flags,			\
+		.read_post = _read_post,				\
+	}
+
+
+static void at24_read_post_vaio(unsigned int off, char *buf, size_t count)
+{
+	int i;
+
+	if (capable(CAP_SYS_ADMIN))
+		return;
+
+	/*
+	 * Hide VAIO private settings to regular users:
+	 * - BIOS passwords: bytes 0x00 to 0x0f
+	 * - UUID: bytes 0x10 to 0x1f
+	 * - Serial number: 0xc0 to 0xdf
+	 */
+	for (i = 0; i < count; i++) {
+		if ((off + i <= 0x1f) ||
+		    (off + i >= 0xc0 && off + i <= 0xdf))
+			buf[i] = 0;
+	}
+}
+
 /* needs 8 addresses as A0-A2 are ignored */
 AT24_CHIP_DATA(at24_data_24c00, 128 / 8, AT24_FLAG_TAKE8ADDR);
 /* old variants can't be handled with this generic entry! */
@@ -144,6 +174,10 @@ AT24_CHIP_DATA(at24_data_24mac602, 64 /
 /* spd is a 24c02 in memory DIMMs */
 AT24_CHIP_DATA(at24_data_spd, 2048 / 8,
 	AT24_FLAG_READONLY | AT24_FLAG_IRUGO);
+/* 24c02_vaio is a 24c02 on some Sony laptops */
+AT24_CHIP_DATA_CB(at24_data_24c02_vaio, 2048 / 8,
+	AT24_FLAG_READONLY | AT24_FLAG_IRUGO,
+	at24_read_post_vaio);
 AT24_CHIP_DATA(at24_data_24c04, 4096 / 8, 0);
 AT24_CHIP_DATA(at24_data_24cs04, 16,
 	AT24_FLAG_SERIAL | AT24_FLAG_READONLY);
@@ -177,6 +211,7 @@ static const struct i2c_device_id at24_i
 	{ "24mac402",	(kernel_ulong_t)&at24_data_24mac402 },
 	{ "24mac602",	(kernel_ulong_t)&at24_data_24mac602 },
 	{ "spd",	(kernel_ulong_t)&at24_data_spd },
+	{ "24c02-vaio",	(kernel_ulong_t)&at24_data_24c02_vaio },
 	{ "24c04",	(kernel_ulong_t)&at24_data_24c04 },
 	{ "24cs04",	(kernel_ulong_t)&at24_data_24cs04 },
 	{ "24c08",	(kernel_ulong_t)&at24_data_24c08 },
@@ -389,6 +424,9 @@ static int at24_read(void *priv, unsigne
 	struct device *dev;
 	char *buf = val;
 	int ret;
+	unsigned int orig_off = off;
+	char *orig_buf = buf;
+	size_t orig_count = count;
 
 	at24 = priv;
 	dev = at24_base_client_dev(at24);
@@ -427,6 +465,9 @@ static int at24_read(void *priv, unsigne
 
 	pm_runtime_put(dev);
 
+	if (unlikely(at24->read_post))
+		at24->read_post(orig_off, orig_buf, orig_count);
+
 	return 0;
 }
 
@@ -654,6 +695,7 @@ static int at24_probe(struct i2c_client
 	at24->byte_len = byte_len;
 	at24->page_size = page_size;
 	at24->flags = flags;
+	at24->read_post = cdata->read_post;
 	at24->num_addresses = num_addresses;
 	at24->offset_adj = at24_get_offset_adj(flags, byte_len);
 	at24->client[0].client = client;


-- 
Jean Delvare
SUSE L3 Support