usb: Add driver for Altus Metrum ChaosKey device (v2)

This is a hardware random number generator. The driver provides both a
/dev/chaoskeyX entry and hooks the entropy source up to the kernel
hwrng interface. More information about the device can be found at
http://chaoskey.org

The USB ID for ChaosKey was allocated from the OpenMoko USB vendor
space and is visible as 'USBtrng' here:

http://wiki.openmoko.org/wiki/USB_Product_IDs

v2: Respond to review from Oliver Neukum <[e-mail]>

* Delete extensive debug infrastructure and replace it with calls to
dev_dbg.

* Allocate I/O buffer separately from device structure to obey
requirements for non-coherant architectures.

* Initialize mutexes before registering device to ensure that open
cannot be invoked before the device is ready to proceed.

* Return number of bytes read instead of -EINTR when partial read
operation is aborted due to a signal.

* Make sure device mutex is unlocked in read error paths.

* Add MAINTAINERS entry for the driver

Signed-off-by: Keith Packard <[e-mail]>
Cc: Oliver Neukum <[e-mail]>
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

MAINTAINERS

···
 F:	drivers/net/usb/cdc_*.c
 F:	include/uapi/linux/usb/cdc.h
 
+USB CHAOSKEY DRIVER
+M:	Keith Packard <[e-mail]>
+L:	[e-mail]
+S:	Maintained
+F:	drivers/usb/misc/chaoskey.c
+
 USB CYPRESS C67X00 DRIVER
 M:	Peter Korsgaard <[e-mail]>
 L:	[e-mail]

drivers/usb/misc/Kconfig

···
 	  This driver is for generating specific traffic for Super Speed Link
 	  Layer Test Device. Say Y only when you want to conduct USB Super Speed
 	  Link Layer Test for host controllers.
+
+config USB_CHAOSKEY
+	tristate "ChaosKey random number generator driver support"
+	help
+	  Say Y here if you want to connect an AltusMetrum ChaosKey to
+	  your computer's USB port. The ChaosKey is a hardware random
+	  number generator which hooks into the kernel entropy pool to
+	  ensure a large supply of entropy for /dev/random and
+	  /dev/urandom and also provides direct access via /dev/chaoskeyX
+
+	  To compile this driver as a module, choose M here: the
+	  module will be called chaoskey.

drivers/usb/misc/Makefile

···
 obj-$(CONFIG_USB_SEVSEG)		+= usbsevseg.o
 obj-$(CONFIG_USB_YUREX)			+= yurex.o
 obj-$(CONFIG_USB_HSIC_USB3503)		+= usb3503.o
+obj-$(CONFIG_USB_CHAOSKEY)		+= chaoskey.o
 
 obj-$(CONFIG_USB_SISUSBVGA)		+= sisusbvga/
 obj-$(CONFIG_USB_LINK_LAYER_TEST)	+= lvstest.o

drivers/usb/misc/chaoskey.c

···
+/*
+ * chaoskey - driver for ChaosKey device from Altus Metrum.
+ *
+ * This device provides true random numbers using a noise source based
+ * on a reverse-biased p-n junction in avalanche breakdown. More
+ * details can be found at http://chaoskey.org
+ *
+ * The driver connects to the kernel hardware RNG interface to provide
+ * entropy for /dev/random and other kernel activities. It also offers
+ * a separate /dev/ entry to allow for direct access to the random
+ * bit stream.
+ *
+ * Copyright © 2015 Keith Packard <[e-mail]>
+ *
+ * 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; version 2 of the License.
+ *
+ * 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.
+ */
+
+#include <linux/module.h>
+#include <linux/slab.h>
+#include <linux/usb.h>
+#include <linux/wait.h>
+#include <linux/hw_random.h>
+
+static struct usb_driver chaoskey_driver;
+static struct usb_class_driver chaoskey_class;
+static int chaoskey_rng_read(struct hwrng *rng, void *data,
+			     size_t max, bool wait);
+
+#define usb_dbg(usb_if, format, arg...) \
+	dev_dbg(&(usb_if)->dev, format, ## arg)
+
+#define usb_err(usb_if, format, arg...) \
+	dev_err(&(usb_if)->dev, format, ## arg)
+
+/* Version Information */
+#define DRIVER_VERSION	"v0.1"
+#define DRIVER_AUTHOR	"Keith Packard, [e-mail]"
+#define DRIVER_DESC	"Altus Metrum ChaosKey driver"
+#define DRIVER_SHORT	"chaoskey"
+
+MODULE_VERSION(DRIVER_VERSION);
+MODULE_AUTHOR(DRIVER_AUTHOR);
+MODULE_DESCRIPTION(DRIVER_DESC);
+MODULE_LICENSE("GPL");
+
+#define CHAOSKEY_VENDOR_ID	0x1d50	/* OpenMoko */
+#define CHAOSKEY_PRODUCT_ID	0x60c6	/* ChaosKey */
+
+#define CHAOSKEY_BUF_LEN	64	/* max size of USB full speed packet */
+
+#define NAK_TIMEOUT (HZ)		/* stall/wait timeout for device */
+
+#ifdef CONFIG_USB_DYNAMIC_MINORS
+#define USB_CHAOSKEY_MINOR_BASE 0
+#else
+
+/* IOWARRIOR_MINOR_BASE + 16, not official yet */
+#define USB_CHAOSKEY_MINOR_BASE 224
+#endif
+
+static const struct usb_device_id chaoskey_table[] = {
+	{ USB_DEVICE(CHAOSKEY_VENDOR_ID, CHAOSKEY_PRODUCT_ID) },
+	{ },
+};
+MODULE_DEVICE_TABLE(usb, chaoskey_table);
+
+/* Driver-local specific stuff */
+struct chaoskey {
+	struct usb_interface *interface;
+	char in_ep;
+	struct mutex lock;
+	struct mutex rng_lock;
+	int open;			/* open count */
+	int present;			/* device not disconnected */
+	int size;			/* size of buf */
+	int valid;			/* bytes of buf read */
+	int used;			/* bytes of buf consumed */
+	char *name;			/* product + serial */
+	struct hwrng hwrng;		/* Embedded struct for hwrng */
+	int hwrng_registered;		/* registered with hwrng API */
+	wait_queue_head_t wait_q;	/* for timeouts */
+	char *buf;
+};
+
+static void chaoskey_free(struct chaoskey *dev)
+{
+	usb_dbg(dev->interface, "free");
+	kfree(dev->name);
+	kfree(dev->buf);
+	kfree(dev);
+}
+
+static int chaoskey_probe(struct usb_interface *interface,
+			  const struct usb_device_id *id)
+{
+	struct usb_device *udev = interface_to_usbdev(interface);
+	struct usb_host_interface *altsetting = interface->cur_altsetting;
+	int i;
+	int in_ep = -1;
+	struct chaoskey *dev;
+	int result;
+	int size;
+
+	usb_dbg(interface, "probe %s-%s", udev->product, udev->serial);
+
+	/* Find the first bulk IN endpoint and its packet size */
+	for (i = 0; i < altsetting->desc.bNumEndpoints; i++) {
+		if (usb_endpoint_is_bulk_in(&altsetting->endpoint[i].desc)) {
+			in_ep = altsetting->endpoint[i].desc.bEndpointAddress;
+			size = altsetting->endpoint[i].desc.wMaxPacketSize;
+			break;
+		}
+	}
+
+	/* Validate endpoint and size */
+	if (in_ep == -1) {
+		usb_dbg(interface, "no IN endpoint found");
+		return -ENODEV;
+	}
+	if (size <= 0) {
+		usb_dbg(interface, "invalid size (%d)", size);
+		return -ENODEV;
+	}
+
+	if (size > CHAOSKEY_BUF_LEN) {
+		usb_dbg(interface, "size reduced from %d to %d\n",
+			size, CHAOSKEY_BUF_LEN);
+		size = CHAOSKEY_BUF_LEN;
+	}
+
+	/* Looks good, allocate and initialize */
+
+	dev = kzalloc(sizeof(struct chaoskey), GFP_KERNEL);
+
+	if (dev == NULL)
+		return -ENOMEM;
+
+	dev->buf = kmalloc(size, GFP_KERNEL);
+
+	if (dev->buf == NULL) {
+		kfree(dev);
+		return -ENOMEM;
+	}
+
+	/* Construct a name using the product and serial values. Each
+	 * device needs a unique name for the hwrng code
+	 */
+
+	if (udev->product && udev->serial) {
+		dev->name = kmalloc(strlen(udev->product) + 1 +
+				    strlen(udev->serial) + 1, GFP_KERNEL);
+		if (dev->name == NULL) {
+			kfree(dev->buf);
+			kfree(dev);
+			return -ENOMEM;
+		}
+
+		strcpy(dev->name, udev->product);
+		strcat(dev->name, "-");
+		strcat(dev->name, udev->serial);
+	}
+
+	dev->interface = interface;
+
+	dev->in_ep = in_ep;
+
+	dev->size = size;
+	dev->present = 1;
+
+	init_waitqueue_head(&dev->wait_q);
+
+	mutex_init(&dev->lock);
+	mutex_init(&dev->rng_lock);
+
+	usb_set_intfdata(interface, dev);
+
+	result = usb_register_dev(interface, &chaoskey_class);
+	if (result) {
+		usb_err(interface, "Unable to allocate minor number.");
+		usb_set_intfdata(interface, NULL);
+		chaoskey_free(dev);
+		return result;
+	}
+
+	dev->hwrng.name = dev->name ? dev->name : chaoskey_driver.name;
+	dev->hwrng.read = chaoskey_rng_read;
+
+	/* Set the 'quality' metric.  Quality is measured in units of
+	 * 1/1024's of a bit ("mills"). This should be set to 1024,
+	 * but there is a bug in the hwrng core which masks it with
+	 * 1023.
+	 *
+	 * The patch that has been merged to the crypto development
+	 * tree for that bug limits the value to 1024 at most, so by
+	 * setting this to 1024 + 1023, we get 1023 before the fix is
+	 * merged and 1024 afterwards. We'll patch this driver once
+	 * both bits of code are in the same tree.
+	 */
+	dev->hwrng.quality = 1024 + 1023;
+
+	dev->hwrng_registered = (hwrng_register(&dev->hwrng) == 0);
+	if (!dev->hwrng_registered)
+		usb_err(interface, "Unable to register with hwrng");
+
+	usb_enable_autosuspend(udev);
+
+	usb_dbg(interface, "chaoskey probe success, size %d", dev->size);
+	return 0;
+}
+
+static void chaoskey_disconnect(struct usb_interface *interface)
+{
+	struct chaoskey	*dev;
+
+	usb_dbg(interface, "disconnect");
+	dev = usb_get_intfdata(interface);
+	if (!dev) {
+		usb_dbg(interface, "disconnect failed - no dev");
+		return;
+	}
+
+	if (dev->hwrng_registered)
+		hwrng_unregister(&dev->hwrng);
+
+	usb_deregister_dev(interface, &chaoskey_class);
+
+	usb_set_intfdata(interface, NULL);
+	mutex_lock(&dev->lock);
+
+	dev->present = 0;
+
+	if (!dev->open) {
+		mutex_unlock(&dev->lock);
+		chaoskey_free(dev);
+	} else
+		mutex_unlock(&dev->lock);
+
+	usb_dbg(interface, "disconnect done");
+}
+
+static int chaoskey_open(struct inode *inode, struct file *file)
+{
+	struct chaoskey *dev;
+	struct usb_interface *interface;
+
+	/* get the interface from minor number and driver information */
+	interface = usb_find_interface(&chaoskey_driver, iminor(inode));
+	if (!interface)
+		return -ENODEV;
+
+	usb_dbg(interface, "open");
+
+	dev = usb_get_intfdata(interface);
+	if (!dev) {
+		usb_dbg(interface, "open (dev)");
+		return -ENODEV;
+	}
+
+	file->private_data = dev;
+	mutex_lock(&dev->lock);
+	++dev->open;
+	mutex_unlock(&dev->lock);
+
+	usb_dbg(interface, "open success");
+	return 0;
+}
+
+static int chaoskey_release(struct inode *inode, struct file *file)
+{
+	struct chaoskey *dev = file->private_data;
+	struct usb_interface *interface;
+
+	if (dev == NULL)
+		return -ENODEV;
+
+	interface = dev->interface;
+
+	usb_dbg(interface, "release");
+
+	mutex_lock(&dev->lock);
+
+	usb_dbg(interface, "open count at release is %d", dev->open);
+
+	if (dev->open <= 0) {
+		usb_dbg(interface, "invalid open count (%d)", dev->open);
+		mutex_unlock(&dev->lock);
+		return -ENODEV;
+	}
+
+	--dev->open;
+
+	if (!dev->present) {
+		if (dev->open == 0) {
+			mutex_unlock(&dev->lock);
+			chaoskey_free(dev);
+		} else
+			mutex_unlock(&dev->lock);
+	} else
+		mutex_unlock(&dev->lock);
+
+	usb_dbg(interface, "release success");
+	return 0;
+}
+
+/* Fill the buffer. Called with dev->lock held
+ */
+static int _chaoskey_fill(struct chaoskey *dev)
+{
+	DEFINE_WAIT(wait);
+	int result;
+	int this_read;
+	struct usb_device *udev = interface_to_usbdev(dev->interface);
+
+	usb_dbg(dev->interface, "fill");
+
+	/* Return immediately if someone called before the buffer was
+	 * empty */
+	if (dev->valid != dev->used) {
+		usb_dbg(dev->interface, "not empty yet (valid %d used %d)",
+			dev->valid, dev->used);
+		return 0;
+	}
+
+	/* Bail if the device has been removed */
+	if (!dev->present) {
+		usb_dbg(dev->interface, "device not present");
+		return -ENODEV;
+	}
+
+	/* Make sure the device is awake */
+	result = usb_autopm_get_interface(dev->interface);
+	if (result) {
+		usb_dbg(dev->interface, "wakeup failed (result %d)", result);
+		return result;
+	}
+
+	result = usb_bulk_msg(udev,
+			      usb_rcvbulkpipe(udev, dev->in_ep),
+			      dev->buf, dev->size, &this_read,
+			      NAK_TIMEOUT);
+
+	/* Let the device go back to sleep eventually */
+	usb_autopm_put_interface(dev->interface);
+
+	if (result == 0) {
+		dev->valid = this_read;
+		dev->used = 0;
+	}
+
+	usb_dbg(dev->interface, "bulk_msg result %d this_read %d",
+		result, this_read);
+
+	return result;
+}
+
+static ssize_t chaoskey_read(struct file *file,
+			     char __user *buffer,
+			     size_t count,
+			     loff_t *ppos)
+{
+	struct chaoskey *dev;
+	ssize_t read_count = 0;
+	int this_time;
+	int result = 0;
+	unsigned long remain;
+
+	dev = file->private_data;
+
+	if (dev == NULL || !dev->present)
+		return -ENODEV;
+
+	usb_dbg(dev->interface, "read %zu", count);
+
+	while (count > 0) {
+
+		/* Grab the rng_lock briefly to ensure that the hwrng interface
+		 * gets priority over other user access
+		 */
+		result = mutex_lock_interruptible(&dev->rng_lock);
+		if (result)
+			goto bail;
+		mutex_unlock(&dev->rng_lock);
+
+		result = mutex_lock_interruptible(&dev->lock);
+		if (result)
+			goto bail;
+		if (dev->valid == dev->used) {
+			result = _chaoskey_fill(dev);
+			if (result) {
+				mutex_unlock(&dev->lock);
+				goto bail;
+			}
+
+			/* Read returned zero bytes */
+			if (dev->used == dev->valid) {
+				mutex_unlock(&dev->lock);
+				goto bail;
+			}
+		}
+
+		this_time = dev->valid - dev->used;
+		if (this_time > count)
+			this_time = count;
+
+		remain = copy_to_user(buffer, dev->buf + dev->used, this_time);
+		if (remain) {
+			result = -EFAULT;
+
+			/* Consume the bytes that were copied so we don't leak
+			 * data to user space
+			 */
+			dev->used += this_time - remain;
+			mutex_unlock(&dev->lock);
+			goto bail;
+		}
+
+		count -= this_time;
+		read_count += this_time;
+		buffer += this_time;
+		dev->used += this_time;
+		mutex_unlock(&dev->lock);
+	}
+bail:
+	if (read_count) {
+		usb_dbg(dev->interface, "read %zu bytes", read_count);
+		return read_count;
+	}
+	usb_dbg(dev->interface, "empty read, result %d", result);
+	return result;
+}
+
+static int chaoskey_rng_read(struct hwrng *rng, void *data,
+			     size_t max, bool wait)
+{
+	struct chaoskey *dev = container_of(rng, struct chaoskey, hwrng);
+	int this_time;
+
+	usb_dbg(dev->interface, "rng_read max %zu wait %d", max, wait);
+
+	if (!dev->present) {
+		usb_dbg(dev->interface, "device not present");
+		return 0;
+	}
+
+	/* Hold the rng_lock until we acquire the device lock so that
+	 * this operation gets priority over other user access to the
+	 * device
+	 */
+	mutex_lock(&dev->rng_lock);
+
+	mutex_lock(&dev->lock);
+
+	mutex_unlock(&dev->rng_lock);
+
+	/* Try to fill the buffer if empty. It doesn't actually matter
+	 * if _chaoskey_fill works; we'll just return zero bytes as
+	 * the buffer will still be empty
+	 */
+	if (dev->valid == dev->used)
+		(void) _chaoskey_fill(dev);
+
+	this_time = dev->valid - dev->used;
+	if (this_time > max)
+		this_time = max;
+
+	memcpy(data, dev->buf, this_time);
+
+	dev->used += this_time;
+
+	mutex_unlock(&dev->lock);
+
+	usb_dbg(dev->interface, "rng_read this_time %d\n", this_time);
+	return this_time;
+}
+
+#ifdef CONFIG_PM
+static int chaoskey_suspend(struct usb_interface *interface,
+			    pm_message_t message)
+{
+	usb_dbg(interface, "suspend");
+	return 0;
+}
+
+static int chaoskey_resume(struct usb_interface *interface)
+{
+	usb_dbg(interface, "resume");
+	return 0;
+}
+#else
+#define chaoskey_suspend NULL
+#define chaoskey_resume NULL
+#endif
+
+/* file operation pointers */
+static const struct file_operations chaoskey_fops = {
+	.owner = THIS_MODULE,
+	.read = chaoskey_read,
+	.open = chaoskey_open,
+	.release = chaoskey_release,
+	.llseek = default_llseek,
+};
+
+/* class driver information */
+static struct usb_class_driver chaoskey_class = {
+	.name = "chaoskey%d",
+	.fops = &chaoskey_fops,
+	.minor_base = USB_CHAOSKEY_MINOR_BASE,
+};
+
+/* usb specific object needed to register this driver with the usb subsystem */
+static struct usb_driver chaoskey_driver = {
+	.name = DRIVER_SHORT,
+	.probe = chaoskey_probe,
+	.disconnect = chaoskey_disconnect,
+	.suspend = chaoskey_suspend,
+	.resume = chaoskey_resume,
+	.reset_resume = chaoskey_resume,
+	.id_table = chaoskey_table,
+	.supports_autosuspend = 1,
+};
+
+module_usb_driver(chaoskey_driver);
+