2 * hw_random/core.c: HWRNG core API
4 * Copyright 2006 Michael Buesch <m@bues.ch>
5 * Copyright 2005 (c) MontaVista Software, Inc.
7 * Please read Documentation/admin-guide/hw_random.rst for details on use.
9 * This software may be used and distributed according to the terms
10 * of the GNU General Public License, incorporated herein by reference.
13 #include <linux/delay.h>
14 #include <linux/device.h>
15 #include <linux/err.h>
17 #include <linux/hw_random.h>
18 #include <linux/random.h>
19 #include <linux/kernel.h>
20 #include <linux/kthread.h>
21 #include <linux/sched/signal.h>
22 #include <linux/miscdevice.h>
23 #include <linux/module.h>
24 #include <linux/random.h>
25 #include <linux/sched.h>
26 #include <linux/slab.h>
27 #include <linux/string.h>
28 #include <linux/uaccess.h>
30 #define RNG_MODULE_NAME "hw_random"
32 #define RNG_BUFFER_SIZE (SMP_CACHE_BYTES < 32 ? 32 : SMP_CACHE_BYTES)
34 static struct hwrng *current_rng;
35 /* the current rng has been explicitly chosen by user via sysfs */
36 static int cur_rng_set_by_user;
37 static struct task_struct *hwrng_fill;
38 /* list of registered rngs, sorted decending by quality */
39 static LIST_HEAD(rng_list);
40 /* Protects rng_list and current_rng */
41 static DEFINE_MUTEX(rng_mutex);
42 /* Protects rng read functions, data_avail, rng_buffer and rng_fillbuf */
43 static DEFINE_MUTEX(reading_mutex);
44 static int data_avail;
45 static u8 *rng_buffer, *rng_fillbuf;
46 static unsigned short current_quality;
47 static unsigned short default_quality; /* = 0; default to "off" */
49 module_param(current_quality, ushort, 0644);
50 MODULE_PARM_DESC(current_quality,
51 "current hwrng entropy estimation per 1024 bits of input");
52 module_param(default_quality, ushort, 0644);
53 MODULE_PARM_DESC(default_quality,
54 "default entropy content of hwrng per 1024 bits of input");
56 static void drop_current_rng(void);
57 static int hwrng_init(struct hwrng *rng);
58 static void start_khwrngd(void);
60 static inline int rng_get_data(struct hwrng *rng, u8 *buffer, size_t size,
63 static size_t rng_buffer_size(void)
65 return RNG_BUFFER_SIZE;
68 static void add_early_randomness(struct hwrng *rng)
71 size_t size = min_t(size_t, 16, rng_buffer_size());
73 mutex_lock(&reading_mutex);
74 bytes_read = rng_get_data(rng, rng_buffer, size, 0);
75 mutex_unlock(&reading_mutex);
77 add_device_randomness(rng_buffer, bytes_read);
80 static inline void cleanup_rng(struct kref *kref)
82 struct hwrng *rng = container_of(kref, struct hwrng, ref);
87 complete(&rng->cleanup_done);
90 static int set_current_rng(struct hwrng *rng)
94 BUG_ON(!mutex_is_locked(&rng_mutex));
96 err = hwrng_init(rng);
106 static void drop_current_rng(void)
108 BUG_ON(!mutex_is_locked(&rng_mutex));
112 /* decrease last reference for triggering the cleanup */
113 kref_put(¤t_rng->ref, cleanup_rng);
117 /* Returns ERR_PTR(), NULL or refcounted hwrng */
118 static struct hwrng *get_current_rng_nolock(void)
121 kref_get(¤t_rng->ref);
126 static struct hwrng *get_current_rng(void)
130 if (mutex_lock_interruptible(&rng_mutex))
131 return ERR_PTR(-ERESTARTSYS);
133 rng = get_current_rng_nolock();
135 mutex_unlock(&rng_mutex);
139 static void put_rng(struct hwrng *rng)
142 * Hold rng_mutex here so we serialize in case they set_current_rng
143 * on rng again immediately.
145 mutex_lock(&rng_mutex);
147 kref_put(&rng->ref, cleanup_rng);
148 mutex_unlock(&rng_mutex);
151 static int hwrng_init(struct hwrng *rng)
153 if (kref_get_unless_zero(&rng->ref))
159 ret = rng->init(rng);
164 kref_init(&rng->ref);
165 reinit_completion(&rng->cleanup_done);
168 current_quality = rng->quality ? : default_quality;
169 if (current_quality > 1024)
170 current_quality = 1024;
172 if (current_quality == 0 && hwrng_fill)
173 kthread_stop(hwrng_fill);
174 if (current_quality > 0 && !hwrng_fill)
180 static int rng_dev_open(struct inode *inode, struct file *filp)
182 /* enforce read-only access to this chrdev */
183 if ((filp->f_mode & FMODE_READ) == 0)
185 if (filp->f_mode & FMODE_WRITE)
190 static inline int rng_get_data(struct hwrng *rng, u8 *buffer, size_t size,
194 BUG_ON(!mutex_is_locked(&reading_mutex));
196 return rng->read(rng, (void *)buffer, size, wait);
198 if (rng->data_present)
199 present = rng->data_present(rng, wait);
204 return rng->data_read(rng, (u32 *)buffer);
209 static ssize_t rng_dev_read(struct file *filp, char __user *buf,
210 size_t size, loff_t *offp)
212 u8 buffer[RNG_BUFFER_SIZE];
219 rng = get_current_rng();
229 if (mutex_lock_interruptible(&reading_mutex)) {
234 bytes_read = rng_get_data(rng, rng_buffer,
236 !(filp->f_flags & O_NONBLOCK));
237 if (bytes_read < 0) {
239 goto out_unlock_reading;
240 } else if (bytes_read == 0 &&
241 (filp->f_flags & O_NONBLOCK)) {
243 goto out_unlock_reading;
246 data_avail = bytes_read;
256 memcpy(buffer, rng_buffer + data_avail, len);
258 mutex_unlock(&reading_mutex);
262 if (copy_to_user(buf + ret, buffer, len)) {
273 schedule_timeout_interruptible(1);
275 if (signal_pending(current)) {
281 memzero_explicit(buffer, sizeof(buffer));
285 mutex_unlock(&reading_mutex);
291 static const struct file_operations rng_chrdev_ops = {
292 .owner = THIS_MODULE,
293 .open = rng_dev_open,
294 .read = rng_dev_read,
295 .llseek = noop_llseek,
298 static const struct attribute_group *rng_dev_groups[];
300 static struct miscdevice rng_miscdev = {
301 .minor = HWRNG_MINOR,
302 .name = RNG_MODULE_NAME,
304 .fops = &rng_chrdev_ops,
305 .groups = rng_dev_groups,
308 static int enable_best_rng(void)
312 BUG_ON(!mutex_is_locked(&rng_mutex));
314 /* rng_list is sorted by quality, use the best (=first) one */
315 if (!list_empty(&rng_list)) {
316 struct hwrng *new_rng;
318 new_rng = list_entry(rng_list.next, struct hwrng, list);
319 ret = ((new_rng == current_rng) ? 0 : set_current_rng(new_rng));
321 cur_rng_set_by_user = 0;
324 cur_rng_set_by_user = 0;
331 static ssize_t hwrng_attr_current_store(struct device *dev,
332 struct device_attribute *attr,
333 const char *buf, size_t len)
336 struct hwrng *rng, *old_rng, *new_rng;
338 err = mutex_lock_interruptible(&rng_mutex);
342 old_rng = current_rng;
343 if (sysfs_streq(buf, "")) {
344 err = enable_best_rng();
346 list_for_each_entry(rng, &rng_list, list) {
347 if (sysfs_streq(rng->name, buf)) {
348 cur_rng_set_by_user = 1;
349 err = set_current_rng(rng);
354 new_rng = get_current_rng_nolock();
355 mutex_unlock(&rng_mutex);
358 if (new_rng != old_rng)
359 add_early_randomness(new_rng);
366 static ssize_t hwrng_attr_current_show(struct device *dev,
367 struct device_attribute *attr,
373 rng = get_current_rng();
377 ret = snprintf(buf, PAGE_SIZE, "%s\n", rng ? rng->name : "none");
383 static ssize_t hwrng_attr_available_show(struct device *dev,
384 struct device_attribute *attr,
390 err = mutex_lock_interruptible(&rng_mutex);
394 list_for_each_entry(rng, &rng_list, list) {
395 strlcat(buf, rng->name, PAGE_SIZE);
396 strlcat(buf, " ", PAGE_SIZE);
398 strlcat(buf, "\n", PAGE_SIZE);
399 mutex_unlock(&rng_mutex);
404 static ssize_t hwrng_attr_selected_show(struct device *dev,
405 struct device_attribute *attr,
408 return snprintf(buf, PAGE_SIZE, "%d\n", cur_rng_set_by_user);
411 static DEVICE_ATTR(rng_current, S_IRUGO | S_IWUSR,
412 hwrng_attr_current_show,
413 hwrng_attr_current_store);
414 static DEVICE_ATTR(rng_available, S_IRUGO,
415 hwrng_attr_available_show,
417 static DEVICE_ATTR(rng_selected, S_IRUGO,
418 hwrng_attr_selected_show,
421 static struct attribute *rng_dev_attrs[] = {
422 &dev_attr_rng_current.attr,
423 &dev_attr_rng_available.attr,
424 &dev_attr_rng_selected.attr,
428 ATTRIBUTE_GROUPS(rng_dev);
430 static void __exit unregister_miscdev(void)
432 misc_deregister(&rng_miscdev);
435 static int __init register_miscdev(void)
437 return misc_register(&rng_miscdev);
440 static int hwrng_fillfn(void *unused)
444 while (!kthread_should_stop()) {
447 rng = get_current_rng();
448 if (IS_ERR(rng) || !rng)
450 mutex_lock(&reading_mutex);
451 rc = rng_get_data(rng, rng_fillbuf,
452 rng_buffer_size(), 1);
453 mutex_unlock(&reading_mutex);
456 pr_warn("hwrng: no data available\n");
457 msleep_interruptible(10000);
460 /* Outside lock, sure, but y'know: randomness. */
461 add_hwgenerator_randomness((void *)rng_fillbuf, rc,
462 rc * current_quality * 8 >> 10);
468 static void start_khwrngd(void)
470 hwrng_fill = kthread_run(hwrng_fillfn, NULL, "hwrng");
471 if (IS_ERR(hwrng_fill)) {
472 pr_err("hwrng_fill thread creation failed\n");
477 int hwrng_register(struct hwrng *rng)
481 struct list_head *rng_list_ptr;
482 bool is_new_current = false;
484 if (!rng->name || (!rng->data_read && !rng->read))
487 mutex_lock(&rng_mutex);
489 /* Must not register two RNGs with the same name. */
491 list_for_each_entry(tmp, &rng_list, list) {
492 if (strcmp(tmp->name, rng->name) == 0)
496 init_completion(&rng->cleanup_done);
497 complete(&rng->cleanup_done);
499 /* rng_list is sorted by decreasing quality */
500 list_for_each(rng_list_ptr, &rng_list) {
501 tmp = list_entry(rng_list_ptr, struct hwrng, list);
502 if (tmp->quality < rng->quality)
505 list_add_tail(&rng->list, rng_list_ptr);
508 (!cur_rng_set_by_user && rng->quality > current_rng->quality)) {
510 * Set new rng as current as the new rng source
511 * provides better entropy quality and was not
512 * chosen by userspace.
514 err = set_current_rng(rng);
517 /* to use current_rng in add_early_randomness() we need
520 is_new_current = true;
523 mutex_unlock(&rng_mutex);
524 if (is_new_current || !rng->init) {
526 * Use a new device's input to add some randomness to
527 * the system. If this rng device isn't going to be
528 * used right away, its init function hasn't been
529 * called yet by set_current_rng(); so only use the
530 * randomness from devices that don't need an init callback
532 add_early_randomness(rng);
538 mutex_unlock(&rng_mutex);
542 EXPORT_SYMBOL_GPL(hwrng_register);
544 void hwrng_unregister(struct hwrng *rng)
546 struct hwrng *old_rng, *new_rng;
549 mutex_lock(&rng_mutex);
551 old_rng = current_rng;
552 list_del(&rng->list);
553 if (current_rng == rng) {
554 err = enable_best_rng();
557 cur_rng_set_by_user = 0;
561 new_rng = get_current_rng_nolock();
562 if (list_empty(&rng_list)) {
563 mutex_unlock(&rng_mutex);
565 kthread_stop(hwrng_fill);
567 mutex_unlock(&rng_mutex);
570 if (old_rng != new_rng)
571 add_early_randomness(new_rng);
575 wait_for_completion(&rng->cleanup_done);
577 EXPORT_SYMBOL_GPL(hwrng_unregister);
579 static void devm_hwrng_release(struct device *dev, void *res)
581 hwrng_unregister(*(struct hwrng **)res);
584 static int devm_hwrng_match(struct device *dev, void *res, void *data)
586 struct hwrng **r = res;
588 if (WARN_ON(!r || !*r))
594 int devm_hwrng_register(struct device *dev, struct hwrng *rng)
599 ptr = devres_alloc(devm_hwrng_release, sizeof(*ptr), GFP_KERNEL);
603 error = hwrng_register(rng);
610 devres_add(dev, ptr);
613 EXPORT_SYMBOL_GPL(devm_hwrng_register);
615 void devm_hwrng_unregister(struct device *dev, struct hwrng *rng)
617 devres_release(dev, devm_hwrng_release, devm_hwrng_match, rng);
619 EXPORT_SYMBOL_GPL(devm_hwrng_unregister);
621 static int __init hwrng_modinit(void)
625 /* kmalloc makes this safe for virt_to_page() in virtio_rng.c */
626 rng_buffer = kmalloc(rng_buffer_size(), GFP_KERNEL);
630 rng_fillbuf = kmalloc(rng_buffer_size(), GFP_KERNEL);
636 ret = register_miscdev();
645 static void __exit hwrng_modexit(void)
647 mutex_lock(&rng_mutex);
651 mutex_unlock(&rng_mutex);
653 unregister_miscdev();
656 module_init(hwrng_modinit);
657 module_exit(hwrng_modexit);
659 MODULE_DESCRIPTION("H/W Random Number Generator (RNG) driver");
660 MODULE_LICENSE("GPL");