xref: /openbmc/linux/drivers/usb/misc/chaoskey.c (revision 6c33a6f4)
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 	dev->hwrng.quality = 1024;
204 
205 	dev->hwrng_registered = (hwrng_register(&dev->hwrng) == 0);
206 	if (!dev->hwrng_registered)
207 		usb_err(interface, "Unable to register with hwrng");
208 
209 	usb_enable_autosuspend(udev);
210 
211 	usb_dbg(interface, "chaoskey probe success, size %d", dev->size);
212 	return 0;
213 
214 out:
215 	usb_set_intfdata(interface, NULL);
216 	chaoskey_free(dev);
217 	return result;
218 }
219 
220 static void chaoskey_disconnect(struct usb_interface *interface)
221 {
222 	struct chaoskey	*dev;
223 
224 	usb_dbg(interface, "disconnect");
225 	dev = usb_get_intfdata(interface);
226 	if (!dev) {
227 		usb_dbg(interface, "disconnect failed - no dev");
228 		return;
229 	}
230 
231 	if (dev->hwrng_registered)
232 		hwrng_unregister(&dev->hwrng);
233 
234 	usb_deregister_dev(interface, &chaoskey_class);
235 
236 	usb_set_intfdata(interface, NULL);
237 	mutex_lock(&dev->lock);
238 
239 	dev->present = false;
240 	usb_poison_urb(dev->urb);
241 
242 	if (!dev->open) {
243 		mutex_unlock(&dev->lock);
244 		chaoskey_free(dev);
245 	} else
246 		mutex_unlock(&dev->lock);
247 
248 	usb_dbg(interface, "disconnect done");
249 }
250 
251 static int chaoskey_open(struct inode *inode, struct file *file)
252 {
253 	struct chaoskey *dev;
254 	struct usb_interface *interface;
255 
256 	/* get the interface from minor number and driver information */
257 	interface = usb_find_interface(&chaoskey_driver, iminor(inode));
258 	if (!interface)
259 		return -ENODEV;
260 
261 	usb_dbg(interface, "open");
262 
263 	dev = usb_get_intfdata(interface);
264 	if (!dev) {
265 		usb_dbg(interface, "open (dev)");
266 		return -ENODEV;
267 	}
268 
269 	file->private_data = dev;
270 	mutex_lock(&dev->lock);
271 	++dev->open;
272 	mutex_unlock(&dev->lock);
273 
274 	usb_dbg(interface, "open success");
275 	return 0;
276 }
277 
278 static int chaoskey_release(struct inode *inode, struct file *file)
279 {
280 	struct chaoskey *dev = file->private_data;
281 	struct usb_interface *interface;
282 
283 	if (dev == NULL)
284 		return -ENODEV;
285 
286 	interface = dev->interface;
287 
288 	usb_dbg(interface, "release");
289 
290 	mutex_lock(&dev->lock);
291 
292 	usb_dbg(interface, "open count at release is %d", dev->open);
293 
294 	if (dev->open <= 0) {
295 		usb_dbg(interface, "invalid open count (%d)", dev->open);
296 		mutex_unlock(&dev->lock);
297 		return -ENODEV;
298 	}
299 
300 	--dev->open;
301 
302 	if (!dev->present) {
303 		if (dev->open == 0) {
304 			mutex_unlock(&dev->lock);
305 			chaoskey_free(dev);
306 		} else
307 			mutex_unlock(&dev->lock);
308 	} else
309 		mutex_unlock(&dev->lock);
310 
311 	usb_dbg(interface, "release success");
312 	return 0;
313 }
314 
315 static void chaos_read_callback(struct urb *urb)
316 {
317 	struct chaoskey *dev = urb->context;
318 	int status = urb->status;
319 
320 	usb_dbg(dev->interface, "callback status (%d)", status);
321 
322 	if (status == 0)
323 		dev->valid = urb->actual_length;
324 	else
325 		dev->valid = 0;
326 
327 	dev->used = 0;
328 
329 	/* must be seen first before validity is announced */
330 	smp_wmb();
331 
332 	dev->reading = false;
333 	wake_up(&dev->wait_q);
334 }
335 
336 /* Fill the buffer. Called with dev->lock held
337  */
338 static int _chaoskey_fill(struct chaoskey *dev)
339 {
340 	DEFINE_WAIT(wait);
341 	int result;
342 	bool started;
343 
344 	usb_dbg(dev->interface, "fill");
345 
346 	/* Return immediately if someone called before the buffer was
347 	 * empty */
348 	if (dev->valid != dev->used) {
349 		usb_dbg(dev->interface, "not empty yet (valid %d used %d)",
350 			dev->valid, dev->used);
351 		return 0;
352 	}
353 
354 	/* Bail if the device has been removed */
355 	if (!dev->present) {
356 		usb_dbg(dev->interface, "device not present");
357 		return -ENODEV;
358 	}
359 
360 	/* Make sure the device is awake */
361 	result = usb_autopm_get_interface(dev->interface);
362 	if (result) {
363 		usb_dbg(dev->interface, "wakeup failed (result %d)", result);
364 		return result;
365 	}
366 
367 	dev->reading = true;
368 	result = usb_submit_urb(dev->urb, GFP_KERNEL);
369 	if (result < 0) {
370 		result = usb_translate_errors(result);
371 		dev->reading = false;
372 		goto out;
373 	}
374 
375 	/* The first read on the Alea takes a little under 2 seconds.
376 	 * Reads after the first read take only a few microseconds
377 	 * though.  Presumably the entropy-generating circuit needs
378 	 * time to ramp up.  So, we wait longer on the first read.
379 	 */
380 	started = dev->reads_started;
381 	dev->reads_started = true;
382 	result = wait_event_interruptible_timeout(
383 		dev->wait_q,
384 		!dev->reading,
385 		(started ? NAK_TIMEOUT : ALEA_FIRST_TIMEOUT) );
386 
387 	if (result < 0) {
388 		usb_kill_urb(dev->urb);
389 		goto out;
390 	}
391 
392 	if (result == 0) {
393 		result = -ETIMEDOUT;
394 		usb_kill_urb(dev->urb);
395 	} else {
396 		result = dev->valid;
397 	}
398 out:
399 	/* Let the device go back to sleep eventually */
400 	usb_autopm_put_interface(dev->interface);
401 
402 	usb_dbg(dev->interface, "read %d bytes", dev->valid);
403 
404 	return result;
405 }
406 
407 static ssize_t chaoskey_read(struct file *file,
408 			     char __user *buffer,
409 			     size_t count,
410 			     loff_t *ppos)
411 {
412 	struct chaoskey *dev;
413 	ssize_t read_count = 0;
414 	int this_time;
415 	int result = 0;
416 	unsigned long remain;
417 
418 	dev = file->private_data;
419 
420 	if (dev == NULL || !dev->present)
421 		return -ENODEV;
422 
423 	usb_dbg(dev->interface, "read %zu", count);
424 
425 	while (count > 0) {
426 
427 		/* Grab the rng_lock briefly to ensure that the hwrng interface
428 		 * gets priority over other user access
429 		 */
430 		result = mutex_lock_interruptible(&dev->rng_lock);
431 		if (result)
432 			goto bail;
433 		mutex_unlock(&dev->rng_lock);
434 
435 		result = mutex_lock_interruptible(&dev->lock);
436 		if (result)
437 			goto bail;
438 		if (dev->valid == dev->used) {
439 			result = _chaoskey_fill(dev);
440 			if (result < 0) {
441 				mutex_unlock(&dev->lock);
442 				goto bail;
443 			}
444 		}
445 
446 		this_time = dev->valid - dev->used;
447 		if (this_time > count)
448 			this_time = count;
449 
450 		remain = copy_to_user(buffer, dev->buf + dev->used, this_time);
451 		if (remain) {
452 			result = -EFAULT;
453 
454 			/* Consume the bytes that were copied so we don't leak
455 			 * data to user space
456 			 */
457 			dev->used += this_time - remain;
458 			mutex_unlock(&dev->lock);
459 			goto bail;
460 		}
461 
462 		count -= this_time;
463 		read_count += this_time;
464 		buffer += this_time;
465 		dev->used += this_time;
466 		mutex_unlock(&dev->lock);
467 	}
468 bail:
469 	if (read_count) {
470 		usb_dbg(dev->interface, "read %zu bytes", read_count);
471 		return read_count;
472 	}
473 	usb_dbg(dev->interface, "empty read, result %d", result);
474 	if (result == -ETIMEDOUT)
475 		result = -EAGAIN;
476 	return result;
477 }
478 
479 static int chaoskey_rng_read(struct hwrng *rng, void *data,
480 			     size_t max, bool wait)
481 {
482 	struct chaoskey *dev = container_of(rng, struct chaoskey, hwrng);
483 	int this_time;
484 
485 	usb_dbg(dev->interface, "rng_read max %zu wait %d", max, wait);
486 
487 	if (!dev->present) {
488 		usb_dbg(dev->interface, "device not present");
489 		return 0;
490 	}
491 
492 	/* Hold the rng_lock until we acquire the device lock so that
493 	 * this operation gets priority over other user access to the
494 	 * device
495 	 */
496 	mutex_lock(&dev->rng_lock);
497 
498 	mutex_lock(&dev->lock);
499 
500 	mutex_unlock(&dev->rng_lock);
501 
502 	/* Try to fill the buffer if empty. It doesn't actually matter
503 	 * if _chaoskey_fill works; we'll just return zero bytes as
504 	 * the buffer will still be empty
505 	 */
506 	if (dev->valid == dev->used)
507 		(void) _chaoskey_fill(dev);
508 
509 	this_time = dev->valid - dev->used;
510 	if (this_time > max)
511 		this_time = max;
512 
513 	memcpy(data, dev->buf + dev->used, this_time);
514 
515 	dev->used += this_time;
516 
517 	mutex_unlock(&dev->lock);
518 
519 	usb_dbg(dev->interface, "rng_read this_time %d\n", this_time);
520 	return this_time;
521 }
522 
523 #ifdef CONFIG_PM
524 static int chaoskey_suspend(struct usb_interface *interface,
525 			    pm_message_t message)
526 {
527 	usb_dbg(interface, "suspend");
528 	return 0;
529 }
530 
531 static int chaoskey_resume(struct usb_interface *interface)
532 {
533 	struct chaoskey *dev;
534 	struct usb_device *udev = interface_to_usbdev(interface);
535 
536 	usb_dbg(interface, "resume");
537 	dev = usb_get_intfdata(interface);
538 
539 	/*
540 	 * We may have lost power.
541 	 * In that case the device that needs a long time
542 	 * for the first requests needs an extended timeout
543 	 * again
544 	 */
545 	if (le16_to_cpu(udev->descriptor.idVendor) == ALEA_VENDOR_ID)
546 		dev->reads_started = false;
547 
548 	return 0;
549 }
550 #else
551 #define chaoskey_suspend NULL
552 #define chaoskey_resume NULL
553 #endif
554 
555 /* file operation pointers */
556 static const struct file_operations chaoskey_fops = {
557 	.owner = THIS_MODULE,
558 	.read = chaoskey_read,
559 	.open = chaoskey_open,
560 	.release = chaoskey_release,
561 	.llseek = default_llseek,
562 };
563 
564 /* class driver information */
565 static struct usb_class_driver chaoskey_class = {
566 	.name = "chaoskey%d",
567 	.fops = &chaoskey_fops,
568 	.minor_base = USB_CHAOSKEY_MINOR_BASE,
569 };
570 
571 /* usb specific object needed to register this driver with the usb subsystem */
572 static struct usb_driver chaoskey_driver = {
573 	.name = DRIVER_SHORT,
574 	.probe = chaoskey_probe,
575 	.disconnect = chaoskey_disconnect,
576 	.suspend = chaoskey_suspend,
577 	.resume = chaoskey_resume,
578 	.reset_resume = chaoskey_resume,
579 	.id_table = chaoskey_table,
580 	.supports_autosuspend = 1,
581 };
582 
583 module_usb_driver(chaoskey_driver);
584 
585