Re: [PATCHv6 1/2] ARM: sunxi: Initial support for Allwinner's SecurityID fuses

From: Emilio López
Date: Sun Sep 01 2013 - 12:48:21 EST

Hi Oliver,

Most of my comments on this are nitpicks, overall it looks good to me

El 01/09/13 08:30, oliver+list@xxxxxxxxxxx escribió:
From: Oliver Schinagl <oliver@xxxxxxxxxxx>

Allwinner has electric fuses (efuse) on their line of chips. This driver
reads those fuses, seeds the kernel entropy and exports them as a sysfs
node.

These fuses are most likely to be programmed at the factory, encoding
things like Chip ID, some sort of serial number etc and appear to be

"..number, etc. and appear.."

reasonable unique.

reasonably

While in theory, these should be writeable by the user, it will probably
be inconvinient to do so. Allwinner recommends that a certain input pin,

inconvenient

labeled 'efuse_vddq', be connected to GND. To write these fuses however,
a 2.5 V programming voltage needs to be applied to this pin.

Even so, they can still be used to generate a board-unique mac from,
board unique RSA key and seed the kernel RNG.

On sun7i additional storage is available, this is initially used for an
UEFI BOOT key, Secure JTAG key, HDMI-HDCP key and vendor specific keys.

Currently supported are the following known chips:
Allwinner sun4i (A10)
Allwinner sun5i (A10s, A13)
Allwinner sun7i (A20)

Signed-off-by: Oliver Schinagl <oliver@xxxxxxxxxxx>
---
Documentation/ABI/testing/sysfs-driver-sunxi-sid | 22 +++
.../bindings/misc/allwinner,sunxi-sid.txt | 17 ++
drivers/misc/eeprom/Kconfig | 13 ++
drivers/misc/eeprom/Makefile | 1 +
drivers/misc/eeprom/sunxi_sid.c | 177 +++++++++++++++++++++
5 files changed, 230 insertions(+)
create mode 100644 Documentation/ABI/testing/sysfs-driver-sunxi-sid
create mode 100644 Documentation/devicetree/bindings/misc/allwinner,sunxi-sid.txt
create mode 100644 drivers/misc/eeprom/sunxi_sid.c

diff --git a/Documentation/ABI/testing/sysfs-driver-sunxi-sid b/Documentation/ABI/testing/sysfs-driver-sunxi-sid
new file mode 100644
index 0000000..ffb9536
--- /dev/null
+++ b/Documentation/ABI/testing/sysfs-driver-sunxi-sid
@@ -0,0 +1,22 @@
+What: /sys/devices/*/<our-device>/eeprom
+Date: August 2013
+Contact: Oliver Schinagl <oliver@xxxxxxxxxxx>
+Description: read-only access to the SID (Security-ID) on current
+ A-series SoC's from Allwinner. Currently supports A10, A10s, A13
+ and A20 CPU's. The earlier A1x series of SoCs exports 16 bytes,
+ whereas the newer A20 SoC exposes 512 bytes split into sections.
+ Besides the 16 bytes of SID, there's also an SJTAG area,
+ HDMI-HDCP key and some custom keys. Below a quick overview, for
+ details see the user manual:
+ 0x000 128 bit root-key (sun[457]i)
+ 0x010 128 bit boot-key (sun7i)
+ 0x020 64 bit security-jtag-key (sun7i)
+ 0x028 16 bit key configuration (sun7i)
+ 0x02b 16 bit custom-vendor-key (sun7i)
+ 0x02c 320 bit low general key (sun7i)
+ 0x040 32 bit read-control access (sun7i)
+ 0x064 224 bit low general key (sun7i)
+ 0x080 2304 bit HDCP-key (sun7i)
+ 0x1a0 768 bit high general key (sun7i)
+Users: any user space application which wants to read the SID on
+ Allwinner's A-series of CPU's.
diff --git a/Documentation/devicetree/bindings/misc/allwinner,sunxi-sid.txt b/Documentation/devicetree/bindings/misc/allwinner,sunxi-sid.txt
new file mode 100644
index 0000000..68ba372
--- /dev/null
+++ b/Documentation/devicetree/bindings/misc/allwinner,sunxi-sid.txt
@@ -0,0 +1,17 @@
+Allwinner sunxi-sid
+
+Required properties:
+- compatible: "allwinner,sun4i-sid" or "allwinner,sun7i-a20-sid".
+- reg: Should contain registers location and length
+
+Example for sun4i:
+ sid@01c23800 {
+ compatible = "allwinner,sun4i-sid";
+ reg = <0x01c23800 0x10>
+ };
+
+Example for sun7i:
+ sid@01c23800 {
+ compatible = "allwinner,sun7i-a20-sid";
+ reg = <0x01c23800 0x200>
+ };
diff --git a/drivers/misc/eeprom/Kconfig b/drivers/misc/eeprom/Kconfig
index 04f2e1f..9536852f 100644
--- a/drivers/misc/eeprom/Kconfig
+++ b/drivers/misc/eeprom/Kconfig
@@ -96,4 +96,17 @@ config EEPROM_DIGSY_MTC_CFG

If unsure, say N.

+config EEPROM_SUNXI_SID
+ tristate "Allwinner sunxi security ID support"
+ depends on ARCH_SUNXI && SYSFS
+ help
+ This is a driver for the 'security ID' available on various Allwinner
+ devices.
+
+ Due to the potential risks involved with changing e-fuses,
+ this driver is read-only.
+
+ This driver can also be built as a module. If so, the module
+ will be called sunxi_sid.
+
endmenu
diff --git a/drivers/misc/eeprom/Makefile b/drivers/misc/eeprom/Makefile
index fc1e81d..9507aec 100644
--- a/drivers/misc/eeprom/Makefile
+++ b/drivers/misc/eeprom/Makefile
@@ -4,4 +4,5 @@ obj-$(CONFIG_EEPROM_LEGACY) += eeprom.o
obj-$(CONFIG_EEPROM_MAX6875) += max6875.o
obj-$(CONFIG_EEPROM_93CX6) += eeprom_93cx6.o
obj-$(CONFIG_EEPROM_93XX46) += eeprom_93xx46.o
+obj-$(CONFIG_EEPROM_SUNXI_SID) += sunxi_sid.o
obj-$(CONFIG_EEPROM_DIGSY_MTC_CFG) += digsy_mtc_eeprom.o
diff --git a/drivers/misc/eeprom/sunxi_sid.c b/drivers/misc/eeprom/sunxi_sid.c
new file mode 100644
index 0000000..39a9a62
--- /dev/null
+++ b/drivers/misc/eeprom/sunxi_sid.c
@@ -0,0 +1,177 @@
+/*
+ * Copyright (c) 2013 Oliver Schinagl <oliver@xxxxxxxxxxx>
+ * http://www.linux-sunxi.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+ * GNU General Public License for more details.
+ *
+ * This driver exposes the Allwinner security ID, efuses exported in byte-
+ * sized chunks.
+ */
+
+#include <linux/compiler.h>
+#include <linux/device.h>
+#include <linux/err.h>
+#include <linux/export.h>
+#include <linux/fs.h>
+#include <linux/init.h>
+#include <linux/io.h>
+#include <linux/kernel.h>
+#include <linux/kobject.h>
+#include <linux/module.h>
+#include <linux/of_device.h>
+#include <linux/platform_device.h>
+#include <linux/random.h>
+#include <linux/slab.h>
+#include <linux/stat.h>
+#include <linux/sysfs.h>
+#include <linux/types.h>
+
+#define DRV_NAME "sunxi-sid"
+
+struct sunxi_sid_data {
+ void __iomem *reg_base;
+ unsigned int keysize;
+};
+
+/* We read the entire key, due to a 32 bit read alignment requirement. Since we
+ * want to return the requested byte, this resuls in somewhat slower code and
+ * uses 4 times more reads as needed but keeps code simpler. Since the SID is
+ * only very rarly probed, this is not really an issue.

rarely

+ */
+static u8 sunxi_sid_read_byte(const struct sunxi_sid_data *sid_data,
+ const unsigned int offset)
+{
+ u32 sid_key;
+
+ if (offset >= sid_data->keysize)
+ return 0;
+
+ sid_key = ioread32be(sid_data->reg_base + round_down(offset, 4));
+ sid_key >>= (offset % 4) * 8;
+
+ return sid_key; /* Only return the last byte */
+}
+
+static ssize_t sid_read(struct file *fd, struct kobject *kobj,
+ struct bin_attribute *attr, char *buf,
+ loff_t pos, size_t size)
+{
+ struct platform_device *pdev;
+ struct sunxi_sid_data *sid_data;
+ int i;
+
+ pdev = to_platform_device(kobj_to_dev(kobj));
+ sid_data = platform_get_drvdata(pdev);
+
+ if (pos < 0 || pos >= sid_data->keysize)
+ return 0;
+ if (size > sid_data->keysize - pos)
+ size = sid_data->keysize - pos;
+
+ for (i = 0; i < size; i++)
+ buf[i] = sunxi_sid_read_byte(sid_data, pos + i);
+
+ return i;
+}
+
+static struct bin_attribute sid_bin_attr = {
+ .attr = { .name = "eeprom", .mode = S_IRUGO, },
+ .read = sid_read,
+};
+
+static struct bin_attribute *sunxi_sid_bin_attrs[] = {
+ &sid_bin_attr,
+ NULL,
+};
+
+static const struct attribute_group sunxi_sid_group = {
+ .bin_attrs = sunxi_sid_bin_attrs,
+};
+
+/* fixme: Unused struct to be used with proper sysfs bin_attr groups */
+static const struct attribute_group *sunxi_sid_groups[] = {
+ &sunxi_sid_group,
+ NULL,
+};
+
+static int sunxi_sid_remove(struct platform_device *pdev)
+{
+ struct sunxi_sid_data *sid_data;
+
+ device_remove_bin_file(&pdev->dev, &sid_bin_attr); /* fixme: remove when using sysfs bin attrs */
+ sid_data = platform_get_drvdata(pdev);
+ dev_dbg(&pdev->dev, "driver unloaded\n");
+
+ return 0;
+}
+
+static const struct of_device_id sunxi_sid_of_match[] = {
+ { .compatible = "allwinner,sun4i-sid", .data = (void *)16},
+ { .compatible = "allwinner,sun7i-a20-sid", .data = (void *)512},
+ {/* sentinel */},
+};
+MODULE_DEVICE_TABLE(of, sunxi_sid_of_match);
+
+static int __init sunxi_sid_probe(struct platform_device *pdev)
+{
+ struct sunxi_sid_data *sid_data;
+ struct resource *res;
+ const struct of_device_id *of_dev_id;
+ u8 *entropy;
+ unsigned int i;
+
+ sid_data = devm_kzalloc(&pdev->dev, sizeof(struct sunxi_sid_data),
+ GFP_KERNEL);
+ if (!sid_data)
+ return -ENOMEM;
+
+ res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+ sid_data->reg_base = devm_ioremap_resource(&pdev->dev, res);
+ if (IS_ERR(sid_data->reg_base))
+ return PTR_ERR(sid_data->reg_base);
+
+ of_dev_id = of_match_device(sunxi_sid_of_match, &pdev->dev);
+ if (!of_dev_id)
+ return -ENODEV;
+ sid_data->keysize = (int)of_dev_id->data;
+
+ platform_set_drvdata(pdev, sid_data);
+
+ sid_bin_attr.size = sid_data->keysize; /* fixme: this should be properly set by the sysfs bin attr groups later */
+ if (device_create_bin_file(&pdev->dev, &sid_bin_attr)) /* fixme: this will need to be removed when using sysfs bin attr groups */
+ return -ENODEV;
+
+ entropy = kzalloc(sizeof(u8) * sid_data->keysize, GFP_KERNEL);
+ for (i = 0; i < sid_data->keysize; i++)
+ entropy[i] = sunxi_sid_read_byte(sid_data, i);
+ add_device_randomness(entropy, sid_data->keysize);
+ kfree(entropy);
+
+ dev_dbg(&pdev->dev, "loaded\n");
+
+ return 0;
+}
+
+static struct platform_driver sunxi_sid_driver = {
+ .probe = sunxi_sid_probe,
+ .remove = sunxi_sid_remove,
+ .driver = {
+ .name = DRV_NAME,
+ .owner = THIS_MODULE,
+ .of_match_table = sunxi_sid_of_match,
+ /* .groups = sunxi_sid_groups, fixme: this is the proper way using bin attr groups */
+ },
+};
+module_platform_driver(sunxi_sid_driver);

As the probe function is marked __init, and this is a non-hotpluggable device, I think you should use module_platform_driver_probe(...) instead of module_platform_driver(...)

+
+MODULE_AUTHOR("Oliver Schinagl <oliver@xxxxxxxxxxx>");
+MODULE_DESCRIPTION("Allwinner sunxi security id driver");
+MODULE_LICENSE("GPL");


Thanks for working on this!

Emilio
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