xref: /openbmc/linux/drivers/usb/misc/chaoskey.c (revision 3bf90eca)
1 // SPDX-License-Identifier: GPL-2.0
2 /*
3  * chaoskey - driver for ChaosKey device from Altus Metrum.
4  *
5  * This device provides true random numbers using a noise source based
6  * on a reverse-biased p-n junction in avalanche breakdown. More
7  * details can be found at http://chaoskey.org
8  *
9  * The driver connects to the kernel hardware RNG interface to provide
10  * entropy for /dev/random and other kernel activities. It also offers
11  * a separate /dev/ entry to allow for direct access to the random
12  * bit stream.
13  *
14  * Copyright © 2015 Keith Packard <keithp@keithp.com>
15  */
16 
17 #include <linux/module.h>
18 #include <linux/slab.h>
19 #include <linux/usb.h>
20 #include <linux/wait.h>
21 #include <linux/hw_random.h>
22 #include <linux/mutex.h>
23 #include <linux/uaccess.h>
24 
25 static struct usb_driver chaoskey_driver;
26 static struct usb_class_driver chaoskey_class;
27 static int chaoskey_rng_read(struct hwrng *rng, void *data,
28 			     size_t max, bool wait);
29 
30 #define usb_dbg(usb_if, format, arg...) \
31 	dev_dbg(&(usb_if)->dev, format, ## arg)
32 
33 #define usb_err(usb_if, format, arg...) \
34 	dev_err(&(usb_if)->dev, format, ## arg)
35 
36 /* Version Information */
37 #define DRIVER_AUTHOR	"Keith Packard, keithp@keithp.com"
38 #define DRIVER_DESC	"Altus Metrum ChaosKey driver"
39 #define DRIVER_SHORT	"chaoskey"
40 
41 MODULE_AUTHOR(DRIVER_AUTHOR);
42 MODULE_DESCRIPTION(DRIVER_DESC);
43 MODULE_LICENSE("GPL");
44 
45 #define CHAOSKEY_VENDOR_ID	0x1d50	/* OpenMoko */
46 #define CHAOSKEY_PRODUCT_ID	0x60c6	/* ChaosKey */
47 
48 #define ALEA_VENDOR_ID		0x12d8	/* Araneus */
49 #define ALEA_PRODUCT_ID		0x0001	/* Alea I */
50 
51 #define CHAOSKEY_BUF_LEN	64	/* max size of USB full speed packet */
52 
53 #define NAK_TIMEOUT (HZ)		/* normal stall/wait timeout */
54 #define ALEA_FIRST_TIMEOUT (HZ*3)	/* first stall/wait timeout for Alea */
55 
56 #ifdef CONFIG_USB_DYNAMIC_MINORS
57 #define USB_CHAOSKEY_MINOR_BASE 0
58 #else
59 
60 /* IOWARRIOR_MINOR_BASE + 16, not official yet */
61 #define USB_CHAOSKEY_MINOR_BASE 224
62 #endif
63 
64 static const struct usb_device_id chaoskey_table[] = {
65 	{ USB_DEVICE(CHAOSKEY_VENDOR_ID, CHAOSKEY_PRODUCT_ID) },
66 	{ USB_DEVICE(ALEA_VENDOR_ID, ALEA_PRODUCT_ID) },
67 	{ },
68 };
69 MODULE_DEVICE_TABLE(usb, chaoskey_table);
70 
71 static void chaos_read_callback(struct urb *urb);
72 
73 /* Driver-local specific stuff */
74 struct chaoskey {
75 	struct usb_interface *interface;
76 	char in_ep;
77 	struct mutex lock;
78 	struct mutex rng_lock;
79 	int open;			/* open count */
80 	bool present;			/* device not disconnected */
81 	bool reading;			/* ongoing IO */
82 	bool reads_started;		/* track first read for Alea */
83 	int size;			/* size of buf */
84 	int valid;			/* bytes of buf read */
85 	int used;			/* bytes of buf consumed */
86 	char *name;			/* product + serial */
87 	struct hwrng hwrng;		/* Embedded struct for hwrng */
88 	int hwrng_registered;		/* registered with hwrng API */
89 	wait_queue_head_t wait_q;	/* for timeouts */
90 	struct urb *urb;		/* for performing IO */
91 	char *buf;
92 };
93 
94 static void chaoskey_free(struct chaoskey *dev)
95 {
96 	if (dev) {
97 		usb_dbg(dev->interface, "free");
98 		usb_free_urb(dev->urb);
99 		kfree(dev->name);
100 		kfree(dev->buf);
101 		usb_put_intf(dev->interface);
102 		kfree(dev);
103 	}
104 }
105 
106 static int chaoskey_probe(struct usb_interface *interface,
107 			  const struct usb_device_id *id)
108 {
109 	struct usb_device *udev = interface_to_usbdev(interface);
110 	struct usb_host_interface *altsetting = interface->cur_altsetting;
111 	struct usb_endpoint_descriptor *epd;
112 	int in_ep;
113 	struct chaoskey *dev;
114 	int result = -ENOMEM;
115 	int size;
116 	int res;
117 
118 	usb_dbg(interface, "probe %s-%s", udev->product, udev->serial);
119 
120 	/* Find the first bulk IN endpoint and its packet size */
121 	res = usb_find_bulk_in_endpoint(altsetting, &epd);
122 	if (res) {
123 		usb_dbg(interface, "no IN endpoint found");
124 		return res;
125 	}
126 
127 	in_ep = usb_endpoint_num(epd);
128 	size = usb_endpoint_maxp(epd);
129 
130 	/* Validate endpoint and size */
131 	if (size <= 0) {
132 		usb_dbg(interface, "invalid size (%d)", size);
133 		return -ENODEV;
134 	}
135 
136 	if (size > CHAOSKEY_BUF_LEN) {
137 		usb_dbg(interface, "size reduced from %d to %d\n",
138 			size, CHAOSKEY_BUF_LEN);
139 		size = CHAOSKEY_BUF_LEN;
140 	}
141 
142 	/* Looks good, allocate and initialize */
143 
144 	dev = kzalloc(sizeof(struct chaoskey), GFP_KERNEL);
145 
146 	if (dev == NULL)
147 		goto out;
148 
149 	dev->interface = usb_get_intf(interface);
150 
151 	dev->buf = kmalloc(size, GFP_KERNEL);
152 
153 	if (dev->buf == NULL)
154 		goto out;
155 
156 	dev->urb = usb_alloc_urb(0, GFP_KERNEL);
157 
158 	if (!dev->urb)
159 		goto out;
160 
161 	usb_fill_bulk_urb(dev->urb,
162 		udev,
163 		usb_rcvbulkpipe(udev, in_ep),
164 		dev->buf,
165 		size,
166 		chaos_read_callback,
167 		dev);
168 
169 	/* Construct a name using the product and serial values. Each
170 	 * device needs a unique name for the hwrng code
171 	 */
172 
173 	if (udev->product && udev->serial) {
174 		dev->name = kasprintf(GFP_KERNEL, "%s-%s", udev->product,
175 				      udev->serial);
176 		if (dev->name == NULL)
177 			goto out;
178 	}
179 
180 	dev->in_ep = in_ep;
181 
182 	if (le16_to_cpu(udev->descriptor.idVendor) != ALEA_VENDOR_ID)
183 		dev->reads_started = true;
184 
185 	dev->size = size;
186 	dev->present = true;
187 
188 	init_waitqueue_head(&dev->wait_q);
189 
190 	mutex_init(&dev->lock);
191 	mutex_init(&dev->rng_lock);
192 
193 	usb_set_intfdata(interface, dev);
194 
195 	result = usb_register_dev(interface, &chaoskey_class);
196 	if (result) {
197 		usb_err(interface, "Unable to allocate minor number.");
198 		goto out;
199 	}
200 
201 	dev->hwrng.name = dev->name ? dev->name : chaoskey_driver.name;
202 	dev->hwrng.read = chaoskey_rng_read;
203 
204 	dev->hwrng_registered = (hwrng_register(&dev->hwrng) == 0);
205 	if (!dev->hwrng_registered)
206 		usb_err(interface, "Unable to register with hwrng");
207 
208 	usb_enable_autosuspend(udev);
209 
210 	usb_dbg(interface, "chaoskey probe success, size %d", dev->size);
211 	return 0;
212 
213 out:
214 	usb_set_intfdata(interface, NULL);
215 	chaoskey_free(dev);
216 	return result;
217 }
218 
219 static void chaoskey_disconnect(struct usb_interface *interface)
220 {
221 	struct chaoskey	*dev;
222 
223 	usb_dbg(interface, "disconnect");
224 	dev = usb_get_intfdata(interface);
225 	if (!dev) {
226 		usb_dbg(interface, "disconnect failed - no dev");
227 		return;
228 	}
229 
230 	if (dev->hwrng_registered)
231 		hwrng_unregister(&dev->hwrng);
232 
233 	usb_deregister_dev(interface, &chaoskey_class);
234 
235 	usb_set_intfdata(interface, NULL);
236 	mutex_lock(&dev->lock);
237 
238 	dev->present = false;
239 	usb_poison_urb(dev->urb);
240 
241 	if (!dev->open) {
242 		mutex_unlock(&dev->lock);
243 		chaoskey_free(dev);
244 	} else
245 		mutex_unlock(&dev->lock);
246 
247 	usb_dbg(interface, "disconnect done");
248 }
249 
250 static int chaoskey_open(struct inode *inode, struct file *file)
251 {
252 	struct chaoskey *dev;
253 	struct usb_interface *interface;
254 
255 	/* get the interface from minor number and driver information */
256 	interface = usb_find_interface(&chaoskey_driver, iminor(inode));
257 	if (!interface)
258 		return -ENODEV;
259 
260 	usb_dbg(interface, "open");
261 
262 	dev = usb_get_intfdata(interface);
263 	if (!dev) {
264 		usb_dbg(interface, "open (dev)");
265 		return -ENODEV;
266 	}
267 
268 	file->private_data = dev;
269 	mutex_lock(&dev->lock);
270 	++dev->open;
271 	mutex_unlock(&dev->lock);
272 
273 	usb_dbg(interface, "open success");
274 	return 0;
275 }
276 
277 static int chaoskey_release(struct inode *inode, struct file *file)
278 {
279 	struct chaoskey *dev = file->private_data;
280 	struct usb_interface *interface;
281 
282 	if (dev == NULL)
283 		return -ENODEV;
284 
285 	interface = dev->interface;
286 
287 	usb_dbg(interface, "release");
288 
289 	mutex_lock(&dev->lock);
290 
291 	usb_dbg(interface, "open count at release is %d", dev->open);
292 
293 	if (dev->open <= 0) {
294 		usb_dbg(interface, "invalid open count (%d)", dev->open);
295 		mutex_unlock(&dev->lock);
296 		return -ENODEV;
297 	}
298 
299 	--dev->open;
300 
301 	if (!dev->present) {
302 		if (dev->open == 0) {
303 			mutex_unlock(&dev->lock);
304 			chaoskey_free(dev);
305 		} else
306 			mutex_unlock(&dev->lock);
307 	} else
308 		mutex_unlock(&dev->lock);
309 
310 	usb_dbg(interface, "release success");
311 	return 0;
312 }
313 
314 static void chaos_read_callback(struct urb *urb)
315 {
316 	struct chaoskey *dev = urb->context;
317 	int status = urb->status;
318 
319 	usb_dbg(dev->interface, "callback status (%d)", status);
320 
321 	if (status == 0)
322 		dev->valid = urb->actual_length;
323 	else
324 		dev->valid = 0;
325 
326 	dev->used = 0;
327 
328 	/* must be seen first before validity is announced */
329 	smp_wmb();
330 
331 	dev->reading = false;
332 	wake_up(&dev->wait_q);
333 }
334 
335 /* Fill the buffer. Called with dev->lock held
336  */
337 static int _chaoskey_fill(struct chaoskey *dev)
338 {
339 	DEFINE_WAIT(wait);
340 	int result;
341 	bool started;
342 
343 	usb_dbg(dev->interface, "fill");
344 
345 	/* Return immediately if someone called before the buffer was
346 	 * empty */
347 	if (dev->valid != dev->used) {
348 		usb_dbg(dev->interface, "not empty yet (valid %d used %d)",
349 			dev->valid, dev->used);
350 		return 0;
351 	}
352 
353 	/* Bail if the device has been removed */
354 	if (!dev->present) {
355 		usb_dbg(dev->interface, "device not present");
356 		return -ENODEV;
357 	}
358 
359 	/* Make sure the device is awake */
360 	result = usb_autopm_get_interface(dev->interface);
361 	if (result) {
362 		usb_dbg(dev->interface, "wakeup failed (result %d)", result);
363 		return result;
364 	}
365 
366 	dev->reading = true;
367 	result = usb_submit_urb(dev->urb, GFP_KERNEL);
368 	if (result < 0) {
369 		result = usb_translate_errors(result);
370 		dev->reading = false;
371 		goto out;
372 	}
373 
374 	/* The first read on the Alea takes a little under 2 seconds.
375 	 * Reads after the first read take only a few microseconds
376 	 * though.  Presumably the entropy-generating circuit needs
377 	 * time to ramp up.  So, we wait longer on the first read.
378 	 */
379 	started = dev->reads_started;
380 	dev->reads_started = true;
381 	result = wait_event_interruptible_timeout(
382 		dev->wait_q,
383 		!dev->reading,
384 		(started ? NAK_TIMEOUT : ALEA_FIRST_TIMEOUT) );
385 
386 	if (result < 0) {
387 		usb_kill_urb(dev->urb);
388 		goto out;
389 	}
390 
391 	if (result == 0) {
392 		result = -ETIMEDOUT;
393 		usb_kill_urb(dev->urb);
394 	} else {
395 		result = dev->valid;
396 	}
397 out:
398 	/* Let the device go back to sleep eventually */
399 	usb_autopm_put_interface(dev->interface);
400 
401 	usb_dbg(dev->interface, "read %d bytes", dev->valid);
402 
403 	return result;
404 }
405 
406 static ssize_t chaoskey_read(struct file *file,
407 			     char __user *buffer,
408 			     size_t count,
409 			     loff_t *ppos)
410 {
411 	struct chaoskey *dev;
412 	ssize_t read_count = 0;
413 	int this_time;
414 	int result = 0;
415 	unsigned long remain;
416 
417 	dev = file->private_data;
418 
419 	if (dev == NULL || !dev->present)
420 		return -ENODEV;
421 
422 	usb_dbg(dev->interface, "read %zu", count);
423 
424 	while (count > 0) {
425 
426 		/* Grab the rng_lock briefly to ensure that the hwrng interface
427 		 * gets priority over other user access
428 		 */
429 		result = mutex_lock_interruptible(&dev->rng_lock);
430 		if (result)
431 			goto bail;
432 		mutex_unlock(&dev->rng_lock);
433 
434 		result = mutex_lock_interruptible(&dev->lock);
435 		if (result)
436 			goto bail;
437 		if (dev->valid == dev->used) {
438 			result = _chaoskey_fill(dev);
439 			if (result < 0) {
440 				mutex_unlock(&dev->lock);
441 				goto bail;
442 			}
443 		}
444 
445 		this_time = dev->valid - dev->used;
446 		if (this_time > count)
447 			this_time = count;
448 
449 		remain = copy_to_user(buffer, dev->buf + dev->used, this_time);
450 		if (remain) {
451 			result = -EFAULT;
452 
453 			/* Consume the bytes that were copied so we don't leak
454 			 * data to user space
455 			 */
456 			dev->used += this_time - remain;
457 			mutex_unlock(&dev->lock);
458 			goto bail;
459 		}
460 
461 		count -= this_time;
462 		read_count += this_time;
463 		buffer += this_time;
464 		dev->used += this_time;
465 		mutex_unlock(&dev->lock);
466 	}
467 bail:
468 	if (read_count) {
469 		usb_dbg(dev->interface, "read %zu bytes", read_count);
470 		return read_count;
471 	}
472 	usb_dbg(dev->interface, "empty read, result %d", result);
473 	if (result == -ETIMEDOUT)
474 		result = -EAGAIN;
475 	return result;
476 }
477 
478 static int chaoskey_rng_read(struct hwrng *rng, void *data,
479 			     size_t max, bool wait)
480 {
481 	struct chaoskey *dev = container_of(rng, struct chaoskey, hwrng);
482 	int this_time;
483 
484 	usb_dbg(dev->interface, "rng_read max %zu wait %d", max, wait);
485 
486 	if (!dev->present) {
487 		usb_dbg(dev->interface, "device not present");
488 		return 0;
489 	}
490 
491 	/* Hold the rng_lock until we acquire the device lock so that
492 	 * this operation gets priority over other user access to the
493 	 * device
494 	 */
495 	mutex_lock(&dev->rng_lock);
496 
497 	mutex_lock(&dev->lock);
498 
499 	mutex_unlock(&dev->rng_lock);
500 
501 	/* Try to fill the buffer if empty. It doesn't actually matter
502 	 * if _chaoskey_fill works; we'll just return zero bytes as
503 	 * the buffer will still be empty
504 	 */
505 	if (dev->valid == dev->used)
506 		(void) _chaoskey_fill(dev);
507 
508 	this_time = dev->valid - dev->used;
509 	if (this_time > max)
510 		this_time = max;
511 
512 	memcpy(data, dev->buf + dev->used, this_time);
513 
514 	dev->used += this_time;
515 
516 	mutex_unlock(&dev->lock);
517 
518 	usb_dbg(dev->interface, "rng_read this_time %d\n", this_time);
519 	return this_time;
520 }
521 
522 #ifdef CONFIG_PM
523 static int chaoskey_suspend(struct usb_interface *interface,
524 			    pm_message_t message)
525 {
526 	usb_dbg(interface, "suspend");
527 	return 0;
528 }
529 
530 static int chaoskey_resume(struct usb_interface *interface)
531 {
532 	struct chaoskey *dev;
533 	struct usb_device *udev = interface_to_usbdev(interface);
534 
535 	usb_dbg(interface, "resume");
536 	dev = usb_get_intfdata(interface);
537 
538 	/*
539 	 * We may have lost power.
540 	 * In that case the device that needs a long time
541 	 * for the first requests needs an extended timeout
542 	 * again
543 	 */
544 	if (le16_to_cpu(udev->descriptor.idVendor) == ALEA_VENDOR_ID)
545 		dev->reads_started = false;
546 
547 	return 0;
548 }
549 #else
550 #define chaoskey_suspend NULL
551 #define chaoskey_resume NULL
552 #endif
553 
554 /* file operation pointers */
555 static const struct file_operations chaoskey_fops = {
556 	.owner = THIS_MODULE,
557 	.read = chaoskey_read,
558 	.open = chaoskey_open,
559 	.release = chaoskey_release,
560 	.llseek = default_llseek,
561 };
562 
563 /* class driver information */
564 static struct usb_class_driver chaoskey_class = {
565 	.name = "chaoskey%d",
566 	.fops = &chaoskey_fops,
567 	.minor_base = USB_CHAOSKEY_MINOR_BASE,
568 };
569 
570 /* usb specific object needed to register this driver with the usb subsystem */
571 static struct usb_driver chaoskey_driver = {
572 	.name = DRIVER_SHORT,
573 	.probe = chaoskey_probe,
574 	.disconnect = chaoskey_disconnect,
575 	.suspend = chaoskey_suspend,
576 	.resume = chaoskey_resume,
577 	.reset_resume = chaoskey_resume,
578 	.id_table = chaoskey_table,
579 	.supports_autosuspend = 1,
580 };
581 
582 module_usb_driver(chaoskey_driver);
583 
584