1 /*
2 * hw_random/core.c: HWRNG core API
3 *
4 * Copyright 2006 Michael Buesch <m@bues.ch>
5 * Copyright 2005 (c) MontaVista Software, Inc.
6 *
7 * Please read Documentation/hw_random.txt for details on use.
8 *
9 * This software may be used and distributed according to the terms
10 * of the GNU General Public License, incorporated herein by reference.
11 */
12
13 #include <linux/delay.h>
14 #include <linux/device.h>
15 #include <linux/err.h>
16 #include <linux/fs.h>
17 #include <linux/hw_random.h>
18 #include <linux/kernel.h>
19 #include <linux/kthread.h>
20 #include <linux/sched/signal.h>
21 #include <linux/miscdevice.h>
22 #include <linux/module.h>
23 #include <linux/random.h>
24 #include <linux/sched.h>
25 #include <linux/slab.h>
26 #include <linux/uaccess.h>
27
28 #define RNG_MODULE_NAME "hw_random"
29
30 static struct hwrng *current_rng;
31 /* the current rng has been explicitly chosen by user via sysfs */
32 static int cur_rng_set_by_user;
33 static struct task_struct *hwrng_fill;
34 /* list of registered rngs, sorted decending by quality */
35 static LIST_HEAD(rng_list);
36 /* Protects rng_list and current_rng */
37 static DEFINE_MUTEX(rng_mutex);
38 /* Protects rng read functions, data_avail, rng_buffer and rng_fillbuf */
39 static DEFINE_MUTEX(reading_mutex);
40 static int data_avail;
41 static u8 *rng_buffer, *rng_fillbuf;
42 static unsigned short current_quality;
43 static unsigned short default_quality; /* = 0; default to "off" */
44
45 module_param(current_quality, ushort, 0644);
46 MODULE_PARM_DESC(current_quality,
47 "current hwrng entropy estimation per mill");
48 module_param(default_quality, ushort, 0644);
49 MODULE_PARM_DESC(default_quality,
50 "default entropy content of hwrng per mill");
51
52 static void drop_current_rng(void);
53 static int hwrng_init(struct hwrng *rng);
54 static void start_khwrngd(void);
55
56 static inline int rng_get_data(struct hwrng *rng, u8 *buffer, size_t size,
57 int wait);
58
rng_buffer_size(void)59 static size_t rng_buffer_size(void)
60 {
61 return SMP_CACHE_BYTES < 32 ? 32 : SMP_CACHE_BYTES;
62 }
63
add_early_randomness(struct hwrng * rng)64 static void add_early_randomness(struct hwrng *rng)
65 {
66 int bytes_read;
67 size_t size = min_t(size_t, 16, rng_buffer_size());
68
69 mutex_lock(&reading_mutex);
70 bytes_read = rng_get_data(rng, rng_buffer, size, 0);
71 mutex_unlock(&reading_mutex);
72 if (bytes_read > 0)
73 add_device_randomness(rng_buffer, bytes_read);
74 }
75
cleanup_rng(struct kref * kref)76 static inline void cleanup_rng(struct kref *kref)
77 {
78 struct hwrng *rng = container_of(kref, struct hwrng, ref);
79
80 if (rng->cleanup)
81 rng->cleanup(rng);
82
83 complete(&rng->cleanup_done);
84 }
85
set_current_rng(struct hwrng * rng)86 static int set_current_rng(struct hwrng *rng)
87 {
88 int err;
89
90 BUG_ON(!mutex_is_locked(&rng_mutex));
91
92 err = hwrng_init(rng);
93 if (err)
94 return err;
95
96 drop_current_rng();
97 current_rng = rng;
98
99 return 0;
100 }
101
drop_current_rng(void)102 static void drop_current_rng(void)
103 {
104 BUG_ON(!mutex_is_locked(&rng_mutex));
105 if (!current_rng)
106 return;
107
108 /* decrease last reference for triggering the cleanup */
109 kref_put(¤t_rng->ref, cleanup_rng);
110 current_rng = NULL;
111 }
112
113 /* Returns ERR_PTR(), NULL or refcounted hwrng */
get_current_rng(void)114 static struct hwrng *get_current_rng(void)
115 {
116 struct hwrng *rng;
117
118 if (mutex_lock_interruptible(&rng_mutex))
119 return ERR_PTR(-ERESTARTSYS);
120
121 rng = current_rng;
122 if (rng)
123 kref_get(&rng->ref);
124
125 mutex_unlock(&rng_mutex);
126 return rng;
127 }
128
put_rng(struct hwrng * rng)129 static void put_rng(struct hwrng *rng)
130 {
131 /*
132 * Hold rng_mutex here so we serialize in case they set_current_rng
133 * on rng again immediately.
134 */
135 mutex_lock(&rng_mutex);
136 if (rng)
137 kref_put(&rng->ref, cleanup_rng);
138 mutex_unlock(&rng_mutex);
139 }
140
hwrng_init(struct hwrng * rng)141 static int hwrng_init(struct hwrng *rng)
142 {
143 if (kref_get_unless_zero(&rng->ref))
144 goto skip_init;
145
146 if (rng->init) {
147 int ret;
148
149 ret = rng->init(rng);
150 if (ret)
151 return ret;
152 }
153
154 kref_init(&rng->ref);
155 reinit_completion(&rng->cleanup_done);
156
157 skip_init:
158 add_early_randomness(rng);
159
160 current_quality = rng->quality ? : default_quality;
161 if (current_quality > 1024)
162 current_quality = 1024;
163
164 if (current_quality == 0 && hwrng_fill)
165 kthread_stop(hwrng_fill);
166 if (current_quality > 0 && !hwrng_fill)
167 start_khwrngd();
168
169 return 0;
170 }
171
rng_dev_open(struct inode * inode,struct file * filp)172 static int rng_dev_open(struct inode *inode, struct file *filp)
173 {
174 /* enforce read-only access to this chrdev */
175 if ((filp->f_mode & FMODE_READ) == 0)
176 return -EINVAL;
177 if (filp->f_mode & FMODE_WRITE)
178 return -EINVAL;
179 return 0;
180 }
181
rng_get_data(struct hwrng * rng,u8 * buffer,size_t size,int wait)182 static inline int rng_get_data(struct hwrng *rng, u8 *buffer, size_t size,
183 int wait) {
184 int present;
185
186 BUG_ON(!mutex_is_locked(&reading_mutex));
187 if (rng->read)
188 return rng->read(rng, (void *)buffer, size, wait);
189
190 if (rng->data_present)
191 present = rng->data_present(rng, wait);
192 else
193 present = 1;
194
195 if (present)
196 return rng->data_read(rng, (u32 *)buffer);
197
198 return 0;
199 }
200
rng_dev_read(struct file * filp,char __user * buf,size_t size,loff_t * offp)201 static ssize_t rng_dev_read(struct file *filp, char __user *buf,
202 size_t size, loff_t *offp)
203 {
204 ssize_t ret = 0;
205 int err = 0;
206 int bytes_read, len;
207 struct hwrng *rng;
208
209 while (size) {
210 rng = get_current_rng();
211 if (IS_ERR(rng)) {
212 err = PTR_ERR(rng);
213 goto out;
214 }
215 if (!rng) {
216 err = -ENODEV;
217 goto out;
218 }
219
220 if (mutex_lock_interruptible(&reading_mutex)) {
221 err = -ERESTARTSYS;
222 goto out_put;
223 }
224 if (!data_avail) {
225 bytes_read = rng_get_data(rng, rng_buffer,
226 rng_buffer_size(),
227 !(filp->f_flags & O_NONBLOCK));
228 if (bytes_read < 0) {
229 err = bytes_read;
230 goto out_unlock_reading;
231 }
232 data_avail = bytes_read;
233 }
234
235 if (!data_avail) {
236 if (filp->f_flags & O_NONBLOCK) {
237 err = -EAGAIN;
238 goto out_unlock_reading;
239 }
240 } else {
241 len = data_avail;
242 if (len > size)
243 len = size;
244
245 data_avail -= len;
246
247 if (copy_to_user(buf + ret, rng_buffer + data_avail,
248 len)) {
249 err = -EFAULT;
250 goto out_unlock_reading;
251 }
252
253 size -= len;
254 ret += len;
255 }
256
257 mutex_unlock(&reading_mutex);
258 put_rng(rng);
259
260 if (need_resched())
261 schedule_timeout_interruptible(1);
262
263 if (signal_pending(current)) {
264 err = -ERESTARTSYS;
265 goto out;
266 }
267 }
268 out:
269 return ret ? : err;
270
271 out_unlock_reading:
272 mutex_unlock(&reading_mutex);
273 out_put:
274 put_rng(rng);
275 goto out;
276 }
277
278 static const struct file_operations rng_chrdev_ops = {
279 .owner = THIS_MODULE,
280 .open = rng_dev_open,
281 .read = rng_dev_read,
282 .llseek = noop_llseek,
283 };
284
285 static const struct attribute_group *rng_dev_groups[];
286
287 static struct miscdevice rng_miscdev = {
288 .minor = HWRNG_MINOR,
289 .name = RNG_MODULE_NAME,
290 .nodename = "hwrng",
291 .fops = &rng_chrdev_ops,
292 .groups = rng_dev_groups,
293 };
294
hwrng_attr_current_store(struct device * dev,struct device_attribute * attr,const char * buf,size_t len)295 static ssize_t hwrng_attr_current_store(struct device *dev,
296 struct device_attribute *attr,
297 const char *buf, size_t len)
298 {
299 int err;
300 struct hwrng *rng;
301
302 err = mutex_lock_interruptible(&rng_mutex);
303 if (err)
304 return -ERESTARTSYS;
305 err = -ENODEV;
306 list_for_each_entry(rng, &rng_list, list) {
307 if (sysfs_streq(rng->name, buf)) {
308 err = 0;
309 cur_rng_set_by_user = 1;
310 if (rng != current_rng)
311 err = set_current_rng(rng);
312 break;
313 }
314 }
315 mutex_unlock(&rng_mutex);
316
317 return err ? : len;
318 }
319
hwrng_attr_current_show(struct device * dev,struct device_attribute * attr,char * buf)320 static ssize_t hwrng_attr_current_show(struct device *dev,
321 struct device_attribute *attr,
322 char *buf)
323 {
324 ssize_t ret;
325 struct hwrng *rng;
326
327 rng = get_current_rng();
328 if (IS_ERR(rng))
329 return PTR_ERR(rng);
330
331 ret = snprintf(buf, PAGE_SIZE, "%s\n", rng ? rng->name : "none");
332 put_rng(rng);
333
334 return ret;
335 }
336
hwrng_attr_available_show(struct device * dev,struct device_attribute * attr,char * buf)337 static ssize_t hwrng_attr_available_show(struct device *dev,
338 struct device_attribute *attr,
339 char *buf)
340 {
341 int err;
342 struct hwrng *rng;
343
344 err = mutex_lock_interruptible(&rng_mutex);
345 if (err)
346 return -ERESTARTSYS;
347 buf[0] = '\0';
348 list_for_each_entry(rng, &rng_list, list) {
349 strlcat(buf, rng->name, PAGE_SIZE);
350 strlcat(buf, " ", PAGE_SIZE);
351 }
352 strlcat(buf, "\n", PAGE_SIZE);
353 mutex_unlock(&rng_mutex);
354
355 return strlen(buf);
356 }
357
hwrng_attr_selected_show(struct device * dev,struct device_attribute * attr,char * buf)358 static ssize_t hwrng_attr_selected_show(struct device *dev,
359 struct device_attribute *attr,
360 char *buf)
361 {
362 return snprintf(buf, PAGE_SIZE, "%d\n", cur_rng_set_by_user);
363 }
364
365 static DEVICE_ATTR(rng_current, S_IRUGO | S_IWUSR,
366 hwrng_attr_current_show,
367 hwrng_attr_current_store);
368 static DEVICE_ATTR(rng_available, S_IRUGO,
369 hwrng_attr_available_show,
370 NULL);
371 static DEVICE_ATTR(rng_selected, S_IRUGO,
372 hwrng_attr_selected_show,
373 NULL);
374
375 static struct attribute *rng_dev_attrs[] = {
376 &dev_attr_rng_current.attr,
377 &dev_attr_rng_available.attr,
378 &dev_attr_rng_selected.attr,
379 NULL
380 };
381
382 ATTRIBUTE_GROUPS(rng_dev);
383
unregister_miscdev(void)384 static void __exit unregister_miscdev(void)
385 {
386 misc_deregister(&rng_miscdev);
387 }
388
register_miscdev(void)389 static int __init register_miscdev(void)
390 {
391 return misc_register(&rng_miscdev);
392 }
393
hwrng_fillfn(void * unused)394 static int hwrng_fillfn(void *unused)
395 {
396 long rc;
397
398 while (!kthread_should_stop()) {
399 struct hwrng *rng;
400
401 rng = get_current_rng();
402 if (IS_ERR(rng) || !rng)
403 break;
404 mutex_lock(&reading_mutex);
405 rc = rng_get_data(rng, rng_fillbuf,
406 rng_buffer_size(), 1);
407 mutex_unlock(&reading_mutex);
408 put_rng(rng);
409 if (rc <= 0) {
410 pr_warn("hwrng: no data available\n");
411 msleep_interruptible(10000);
412 continue;
413 }
414 /* Outside lock, sure, but y'know: randomness. */
415 add_hwgenerator_randomness((void *)rng_fillbuf, rc,
416 rc * current_quality * 8 >> 10);
417 }
418 hwrng_fill = NULL;
419 return 0;
420 }
421
start_khwrngd(void)422 static void start_khwrngd(void)
423 {
424 hwrng_fill = kthread_run(hwrng_fillfn, NULL, "hwrng");
425 if (IS_ERR(hwrng_fill)) {
426 pr_err("hwrng_fill thread creation failed");
427 hwrng_fill = NULL;
428 }
429 }
430
hwrng_register(struct hwrng * rng)431 int hwrng_register(struct hwrng *rng)
432 {
433 int err = -EINVAL;
434 struct hwrng *old_rng, *tmp;
435 struct list_head *rng_list_ptr;
436
437 if (!rng->name || (!rng->data_read && !rng->read))
438 goto out;
439
440 mutex_lock(&rng_mutex);
441 /* Must not register two RNGs with the same name. */
442 err = -EEXIST;
443 list_for_each_entry(tmp, &rng_list, list) {
444 if (strcmp(tmp->name, rng->name) == 0)
445 goto out_unlock;
446 }
447
448 init_completion(&rng->cleanup_done);
449 complete(&rng->cleanup_done);
450
451 /* rng_list is sorted by decreasing quality */
452 list_for_each(rng_list_ptr, &rng_list) {
453 tmp = list_entry(rng_list_ptr, struct hwrng, list);
454 if (tmp->quality < rng->quality)
455 break;
456 }
457 list_add_tail(&rng->list, rng_list_ptr);
458
459 old_rng = current_rng;
460 err = 0;
461 if (!old_rng ||
462 (!cur_rng_set_by_user && rng->quality > old_rng->quality)) {
463 /*
464 * Set new rng as current as the new rng source
465 * provides better entropy quality and was not
466 * chosen by userspace.
467 */
468 err = set_current_rng(rng);
469 if (err)
470 goto out_unlock;
471 }
472
473 if (old_rng && !rng->init) {
474 /*
475 * Use a new device's input to add some randomness to
476 * the system. If this rng device isn't going to be
477 * used right away, its init function hasn't been
478 * called yet; so only use the randomness from devices
479 * that don't need an init callback.
480 */
481 add_early_randomness(rng);
482 }
483
484 out_unlock:
485 mutex_unlock(&rng_mutex);
486 out:
487 return err;
488 }
489 EXPORT_SYMBOL_GPL(hwrng_register);
490
hwrng_unregister(struct hwrng * rng)491 void hwrng_unregister(struct hwrng *rng)
492 {
493 mutex_lock(&rng_mutex);
494
495 list_del(&rng->list);
496 if (current_rng == rng) {
497 drop_current_rng();
498 cur_rng_set_by_user = 0;
499 /* rng_list is sorted by quality, use the best (=first) one */
500 if (!list_empty(&rng_list)) {
501 struct hwrng *new_rng;
502
503 new_rng = list_entry(rng_list.next, struct hwrng, list);
504 set_current_rng(new_rng);
505 }
506 }
507
508 if (list_empty(&rng_list)) {
509 mutex_unlock(&rng_mutex);
510 if (hwrng_fill)
511 kthread_stop(hwrng_fill);
512 } else
513 mutex_unlock(&rng_mutex);
514
515 wait_for_completion(&rng->cleanup_done);
516 }
517 EXPORT_SYMBOL_GPL(hwrng_unregister);
518
devm_hwrng_release(struct device * dev,void * res)519 static void devm_hwrng_release(struct device *dev, void *res)
520 {
521 hwrng_unregister(*(struct hwrng **)res);
522 }
523
devm_hwrng_match(struct device * dev,void * res,void * data)524 static int devm_hwrng_match(struct device *dev, void *res, void *data)
525 {
526 struct hwrng **r = res;
527
528 if (WARN_ON(!r || !*r))
529 return 0;
530
531 return *r == data;
532 }
533
devm_hwrng_register(struct device * dev,struct hwrng * rng)534 int devm_hwrng_register(struct device *dev, struct hwrng *rng)
535 {
536 struct hwrng **ptr;
537 int error;
538
539 ptr = devres_alloc(devm_hwrng_release, sizeof(*ptr), GFP_KERNEL);
540 if (!ptr)
541 return -ENOMEM;
542
543 error = hwrng_register(rng);
544 if (error) {
545 devres_free(ptr);
546 return error;
547 }
548
549 *ptr = rng;
550 devres_add(dev, ptr);
551 return 0;
552 }
553 EXPORT_SYMBOL_GPL(devm_hwrng_register);
554
devm_hwrng_unregister(struct device * dev,struct hwrng * rng)555 void devm_hwrng_unregister(struct device *dev, struct hwrng *rng)
556 {
557 devres_release(dev, devm_hwrng_release, devm_hwrng_match, rng);
558 }
559 EXPORT_SYMBOL_GPL(devm_hwrng_unregister);
560
hwrng_modinit(void)561 static int __init hwrng_modinit(void)
562 {
563 int ret = -ENOMEM;
564
565 /* kmalloc makes this safe for virt_to_page() in virtio_rng.c */
566 rng_buffer = kmalloc(rng_buffer_size(), GFP_KERNEL);
567 if (!rng_buffer)
568 return -ENOMEM;
569
570 rng_fillbuf = kmalloc(rng_buffer_size(), GFP_KERNEL);
571 if (!rng_fillbuf) {
572 kfree(rng_buffer);
573 return -ENOMEM;
574 }
575
576 ret = register_miscdev();
577 if (ret) {
578 kfree(rng_fillbuf);
579 kfree(rng_buffer);
580 }
581
582 return ret;
583 }
584
hwrng_modexit(void)585 static void __exit hwrng_modexit(void)
586 {
587 mutex_lock(&rng_mutex);
588 BUG_ON(current_rng);
589 kfree(rng_buffer);
590 kfree(rng_fillbuf);
591 mutex_unlock(&rng_mutex);
592
593 unregister_miscdev();
594 }
595
596 module_init(hwrng_modinit);
597 module_exit(hwrng_modexit);
598
599 MODULE_DESCRIPTION("H/W Random Number Generator (RNG) driver");
600 MODULE_LICENSE("GPL");
601