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/admin-guide/hw_random.rst 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 1024 bits of input");
48 module_param(default_quality, ushort, 0644);
49 MODULE_PARM_DESC(default_quality,
50 "default entropy content of hwrng per 1024 bits of input");
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_nolock(void)114 static struct hwrng *get_current_rng_nolock(void)
115 {
116 if (current_rng)
117 kref_get(¤t_rng->ref);
118
119 return current_rng;
120 }
121
get_current_rng(void)122 static struct hwrng *get_current_rng(void)
123 {
124 struct hwrng *rng;
125
126 if (mutex_lock_interruptible(&rng_mutex))
127 return ERR_PTR(-ERESTARTSYS);
128
129 rng = get_current_rng_nolock();
130
131 mutex_unlock(&rng_mutex);
132 return rng;
133 }
134
put_rng(struct hwrng * rng)135 static void put_rng(struct hwrng *rng)
136 {
137 /*
138 * Hold rng_mutex here so we serialize in case they set_current_rng
139 * on rng again immediately.
140 */
141 mutex_lock(&rng_mutex);
142 if (rng)
143 kref_put(&rng->ref, cleanup_rng);
144 mutex_unlock(&rng_mutex);
145 }
146
hwrng_init(struct hwrng * rng)147 static int hwrng_init(struct hwrng *rng)
148 {
149 if (kref_get_unless_zero(&rng->ref))
150 goto skip_init;
151
152 if (rng->init) {
153 int ret;
154
155 ret = rng->init(rng);
156 if (ret)
157 return ret;
158 }
159
160 kref_init(&rng->ref);
161 reinit_completion(&rng->cleanup_done);
162
163 skip_init:
164 current_quality = rng->quality ? : default_quality;
165 if (current_quality > 1024)
166 current_quality = 1024;
167
168 if (current_quality == 0 && hwrng_fill)
169 kthread_stop(hwrng_fill);
170 if (current_quality > 0 && !hwrng_fill)
171 start_khwrngd();
172
173 return 0;
174 }
175
rng_dev_open(struct inode * inode,struct file * filp)176 static int rng_dev_open(struct inode *inode, struct file *filp)
177 {
178 /* enforce read-only access to this chrdev */
179 if ((filp->f_mode & FMODE_READ) == 0)
180 return -EINVAL;
181 if (filp->f_mode & FMODE_WRITE)
182 return -EINVAL;
183 return 0;
184 }
185
rng_get_data(struct hwrng * rng,u8 * buffer,size_t size,int wait)186 static inline int rng_get_data(struct hwrng *rng, u8 *buffer, size_t size,
187 int wait) {
188 int present;
189
190 BUG_ON(!mutex_is_locked(&reading_mutex));
191 if (rng->read)
192 return rng->read(rng, (void *)buffer, size, wait);
193
194 if (rng->data_present)
195 present = rng->data_present(rng, wait);
196 else
197 present = 1;
198
199 if (present)
200 return rng->data_read(rng, (u32 *)buffer);
201
202 return 0;
203 }
204
rng_dev_read(struct file * filp,char __user * buf,size_t size,loff_t * offp)205 static ssize_t rng_dev_read(struct file *filp, char __user *buf,
206 size_t size, loff_t *offp)
207 {
208 ssize_t ret = 0;
209 int err = 0;
210 int bytes_read, len;
211 struct hwrng *rng;
212
213 while (size) {
214 rng = get_current_rng();
215 if (IS_ERR(rng)) {
216 err = PTR_ERR(rng);
217 goto out;
218 }
219 if (!rng) {
220 err = -ENODEV;
221 goto out;
222 }
223
224 if (mutex_lock_interruptible(&reading_mutex)) {
225 err = -ERESTARTSYS;
226 goto out_put;
227 }
228 if (!data_avail) {
229 bytes_read = rng_get_data(rng, rng_buffer,
230 rng_buffer_size(),
231 !(filp->f_flags & O_NONBLOCK));
232 if (bytes_read < 0) {
233 err = bytes_read;
234 goto out_unlock_reading;
235 }
236 data_avail = bytes_read;
237 }
238
239 if (!data_avail) {
240 if (filp->f_flags & O_NONBLOCK) {
241 err = -EAGAIN;
242 goto out_unlock_reading;
243 }
244 } else {
245 len = data_avail;
246 if (len > size)
247 len = size;
248
249 data_avail -= len;
250
251 if (copy_to_user(buf + ret, rng_buffer + data_avail,
252 len)) {
253 err = -EFAULT;
254 goto out_unlock_reading;
255 }
256
257 size -= len;
258 ret += len;
259 }
260
261 mutex_unlock(&reading_mutex);
262 put_rng(rng);
263
264 if (need_resched())
265 schedule_timeout_interruptible(1);
266
267 if (signal_pending(current)) {
268 err = -ERESTARTSYS;
269 goto out;
270 }
271 }
272 out:
273 return ret ? : err;
274
275 out_unlock_reading:
276 mutex_unlock(&reading_mutex);
277 out_put:
278 put_rng(rng);
279 goto out;
280 }
281
282 static const struct file_operations rng_chrdev_ops = {
283 .owner = THIS_MODULE,
284 .open = rng_dev_open,
285 .read = rng_dev_read,
286 .llseek = noop_llseek,
287 };
288
289 static const struct attribute_group *rng_dev_groups[];
290
291 static struct miscdevice rng_miscdev = {
292 .minor = HWRNG_MINOR,
293 .name = RNG_MODULE_NAME,
294 .nodename = "hwrng",
295 .fops = &rng_chrdev_ops,
296 .groups = rng_dev_groups,
297 };
298
enable_best_rng(void)299 static int enable_best_rng(void)
300 {
301 int ret = -ENODEV;
302
303 BUG_ON(!mutex_is_locked(&rng_mutex));
304
305 /* rng_list is sorted by quality, use the best (=first) one */
306 if (!list_empty(&rng_list)) {
307 struct hwrng *new_rng;
308
309 new_rng = list_entry(rng_list.next, struct hwrng, list);
310 ret = ((new_rng == current_rng) ? 0 : set_current_rng(new_rng));
311 if (!ret)
312 cur_rng_set_by_user = 0;
313 } else {
314 drop_current_rng();
315 cur_rng_set_by_user = 0;
316 ret = 0;
317 }
318
319 return ret;
320 }
321
rng_current_store(struct device * dev,struct device_attribute * attr,const char * buf,size_t len)322 static ssize_t rng_current_store(struct device *dev,
323 struct device_attribute *attr,
324 const char *buf, size_t len)
325 {
326 int err;
327 struct hwrng *rng, *old_rng, *new_rng;
328
329 err = mutex_lock_interruptible(&rng_mutex);
330 if (err)
331 return -ERESTARTSYS;
332
333 old_rng = current_rng;
334 if (sysfs_streq(buf, "")) {
335 err = enable_best_rng();
336 } else {
337 list_for_each_entry(rng, &rng_list, list) {
338 if (sysfs_streq(rng->name, buf)) {
339 cur_rng_set_by_user = 1;
340 err = set_current_rng(rng);
341 break;
342 }
343 }
344 }
345 new_rng = get_current_rng_nolock();
346 mutex_unlock(&rng_mutex);
347
348 if (new_rng) {
349 if (new_rng != old_rng)
350 add_early_randomness(new_rng);
351 put_rng(new_rng);
352 }
353
354 return err ? : len;
355 }
356
rng_current_show(struct device * dev,struct device_attribute * attr,char * buf)357 static ssize_t rng_current_show(struct device *dev,
358 struct device_attribute *attr,
359 char *buf)
360 {
361 ssize_t ret;
362 struct hwrng *rng;
363
364 rng = get_current_rng();
365 if (IS_ERR(rng))
366 return PTR_ERR(rng);
367
368 ret = snprintf(buf, PAGE_SIZE, "%s\n", rng ? rng->name : "none");
369 put_rng(rng);
370
371 return ret;
372 }
373
rng_available_show(struct device * dev,struct device_attribute * attr,char * buf)374 static ssize_t rng_available_show(struct device *dev,
375 struct device_attribute *attr,
376 char *buf)
377 {
378 int err;
379 struct hwrng *rng;
380
381 err = mutex_lock_interruptible(&rng_mutex);
382 if (err)
383 return -ERESTARTSYS;
384 buf[0] = '\0';
385 list_for_each_entry(rng, &rng_list, list) {
386 strlcat(buf, rng->name, PAGE_SIZE);
387 strlcat(buf, " ", PAGE_SIZE);
388 }
389 strlcat(buf, "\n", PAGE_SIZE);
390 mutex_unlock(&rng_mutex);
391
392 return strlen(buf);
393 }
394
rng_selected_show(struct device * dev,struct device_attribute * attr,char * buf)395 static ssize_t rng_selected_show(struct device *dev,
396 struct device_attribute *attr,
397 char *buf)
398 {
399 return sysfs_emit(buf, "%d\n", cur_rng_set_by_user);
400 }
401
402 static DEVICE_ATTR_RW(rng_current);
403 static DEVICE_ATTR_RO(rng_available);
404 static DEVICE_ATTR_RO(rng_selected);
405
406 static struct attribute *rng_dev_attrs[] = {
407 &dev_attr_rng_current.attr,
408 &dev_attr_rng_available.attr,
409 &dev_attr_rng_selected.attr,
410 NULL
411 };
412
413 ATTRIBUTE_GROUPS(rng_dev);
414
unregister_miscdev(void)415 static void __exit unregister_miscdev(void)
416 {
417 misc_deregister(&rng_miscdev);
418 }
419
register_miscdev(void)420 static int __init register_miscdev(void)
421 {
422 return misc_register(&rng_miscdev);
423 }
424
hwrng_fillfn(void * unused)425 static int hwrng_fillfn(void *unused)
426 {
427 long rc;
428
429 while (!kthread_should_stop()) {
430 struct hwrng *rng;
431
432 rng = get_current_rng();
433 if (IS_ERR(rng) || !rng)
434 break;
435 mutex_lock(&reading_mutex);
436 rc = rng_get_data(rng, rng_fillbuf,
437 rng_buffer_size(), 1);
438 mutex_unlock(&reading_mutex);
439 put_rng(rng);
440 if (rc <= 0) {
441 pr_warn("hwrng: no data available\n");
442 msleep_interruptible(10000);
443 continue;
444 }
445 /* Outside lock, sure, but y'know: randomness. */
446 add_hwgenerator_randomness((void *)rng_fillbuf, rc,
447 rc * current_quality * 8 >> 10);
448 }
449 hwrng_fill = NULL;
450 return 0;
451 }
452
start_khwrngd(void)453 static void start_khwrngd(void)
454 {
455 hwrng_fill = kthread_run(hwrng_fillfn, NULL, "hwrng");
456 if (IS_ERR(hwrng_fill)) {
457 pr_err("hwrng_fill thread creation failed\n");
458 hwrng_fill = NULL;
459 }
460 }
461
hwrng_register(struct hwrng * rng)462 int hwrng_register(struct hwrng *rng)
463 {
464 int err = -EINVAL;
465 struct hwrng *tmp;
466 struct list_head *rng_list_ptr;
467 bool is_new_current = false;
468
469 if (!rng->name || (!rng->data_read && !rng->read))
470 goto out;
471
472 mutex_lock(&rng_mutex);
473
474 /* Must not register two RNGs with the same name. */
475 err = -EEXIST;
476 list_for_each_entry(tmp, &rng_list, list) {
477 if (strcmp(tmp->name, rng->name) == 0)
478 goto out_unlock;
479 }
480
481 init_completion(&rng->cleanup_done);
482 complete(&rng->cleanup_done);
483
484 /* rng_list is sorted by decreasing quality */
485 list_for_each(rng_list_ptr, &rng_list) {
486 tmp = list_entry(rng_list_ptr, struct hwrng, list);
487 if (tmp->quality < rng->quality)
488 break;
489 }
490 list_add_tail(&rng->list, rng_list_ptr);
491
492 if (!current_rng ||
493 (!cur_rng_set_by_user && rng->quality > current_rng->quality)) {
494 /*
495 * Set new rng as current as the new rng source
496 * provides better entropy quality and was not
497 * chosen by userspace.
498 */
499 err = set_current_rng(rng);
500 if (err)
501 goto out_unlock;
502 /* to use current_rng in add_early_randomness() we need
503 * to take a ref
504 */
505 is_new_current = true;
506 kref_get(&rng->ref);
507 }
508 mutex_unlock(&rng_mutex);
509 if (is_new_current || !rng->init) {
510 /*
511 * Use a new device's input to add some randomness to
512 * the system. If this rng device isn't going to be
513 * used right away, its init function hasn't been
514 * called yet by set_current_rng(); so only use the
515 * randomness from devices that don't need an init callback
516 */
517 add_early_randomness(rng);
518 }
519 if (is_new_current)
520 put_rng(rng);
521 return 0;
522 out_unlock:
523 mutex_unlock(&rng_mutex);
524 out:
525 return err;
526 }
527 EXPORT_SYMBOL_GPL(hwrng_register);
528
hwrng_unregister(struct hwrng * rng)529 void hwrng_unregister(struct hwrng *rng)
530 {
531 struct hwrng *old_rng, *new_rng;
532 int err;
533
534 mutex_lock(&rng_mutex);
535
536 old_rng = current_rng;
537 list_del(&rng->list);
538 if (current_rng == rng) {
539 err = enable_best_rng();
540 if (err) {
541 drop_current_rng();
542 cur_rng_set_by_user = 0;
543 }
544 }
545
546 new_rng = get_current_rng_nolock();
547 if (list_empty(&rng_list)) {
548 mutex_unlock(&rng_mutex);
549 if (hwrng_fill)
550 kthread_stop(hwrng_fill);
551 } else
552 mutex_unlock(&rng_mutex);
553
554 if (new_rng) {
555 if (old_rng != new_rng)
556 add_early_randomness(new_rng);
557 put_rng(new_rng);
558 }
559
560 wait_for_completion(&rng->cleanup_done);
561 }
562 EXPORT_SYMBOL_GPL(hwrng_unregister);
563
devm_hwrng_release(struct device * dev,void * res)564 static void devm_hwrng_release(struct device *dev, void *res)
565 {
566 hwrng_unregister(*(struct hwrng **)res);
567 }
568
devm_hwrng_match(struct device * dev,void * res,void * data)569 static int devm_hwrng_match(struct device *dev, void *res, void *data)
570 {
571 struct hwrng **r = res;
572
573 if (WARN_ON(!r || !*r))
574 return 0;
575
576 return *r == data;
577 }
578
devm_hwrng_register(struct device * dev,struct hwrng * rng)579 int devm_hwrng_register(struct device *dev, struct hwrng *rng)
580 {
581 struct hwrng **ptr;
582 int error;
583
584 ptr = devres_alloc(devm_hwrng_release, sizeof(*ptr), GFP_KERNEL);
585 if (!ptr)
586 return -ENOMEM;
587
588 error = hwrng_register(rng);
589 if (error) {
590 devres_free(ptr);
591 return error;
592 }
593
594 *ptr = rng;
595 devres_add(dev, ptr);
596 return 0;
597 }
598 EXPORT_SYMBOL_GPL(devm_hwrng_register);
599
devm_hwrng_unregister(struct device * dev,struct hwrng * rng)600 void devm_hwrng_unregister(struct device *dev, struct hwrng *rng)
601 {
602 devres_release(dev, devm_hwrng_release, devm_hwrng_match, rng);
603 }
604 EXPORT_SYMBOL_GPL(devm_hwrng_unregister);
605
hwrng_modinit(void)606 static int __init hwrng_modinit(void)
607 {
608 int ret;
609
610 /* kmalloc makes this safe for virt_to_page() in virtio_rng.c */
611 rng_buffer = kmalloc(rng_buffer_size(), GFP_KERNEL);
612 if (!rng_buffer)
613 return -ENOMEM;
614
615 rng_fillbuf = kmalloc(rng_buffer_size(), GFP_KERNEL);
616 if (!rng_fillbuf) {
617 kfree(rng_buffer);
618 return -ENOMEM;
619 }
620
621 ret = register_miscdev();
622 if (ret) {
623 kfree(rng_fillbuf);
624 kfree(rng_buffer);
625 }
626
627 return ret;
628 }
629
hwrng_modexit(void)630 static void __exit hwrng_modexit(void)
631 {
632 mutex_lock(&rng_mutex);
633 BUG_ON(current_rng);
634 kfree(rng_buffer);
635 kfree(rng_fillbuf);
636 mutex_unlock(&rng_mutex);
637
638 unregister_miscdev();
639 }
640
641 module_init(hwrng_modinit);
642 module_exit(hwrng_modexit);
643
644 MODULE_DESCRIPTION("H/W Random Number Generator (RNG) driver");
645 MODULE_LICENSE("GPL");
646