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/uaccess.h>
29 #define RNG_MODULE_NAME "hw_random"
31 static struct hwrng *current_rng;
32 /* the current rng has been explicitly chosen by user via sysfs */
33 static int cur_rng_set_by_user;
34 static struct task_struct *hwrng_fill;
35 /* list of registered rngs, sorted decending by quality */
36 static LIST_HEAD(rng_list);
37 /* Protects rng_list and current_rng */
38 static DEFINE_MUTEX(rng_mutex);
39 /* Protects rng read functions, data_avail, rng_buffer and rng_fillbuf */
40 static DEFINE_MUTEX(reading_mutex);
41 static int data_avail;
42 static u8 *rng_buffer, *rng_fillbuf;
43 static unsigned short current_quality;
44 static unsigned short default_quality; /* = 0; default to "off" */
46 module_param(current_quality, ushort, 0644);
47 MODULE_PARM_DESC(current_quality,
48 "current hwrng entropy estimation per 1024 bits of input");
49 module_param(default_quality, ushort, 0644);
50 MODULE_PARM_DESC(default_quality,
51 "default entropy content of hwrng per 1024 bits of input");
53 static void drop_current_rng(void);
54 static int hwrng_init(struct hwrng *rng);
55 static void start_khwrngd(void);
57 static inline int rng_get_data(struct hwrng *rng, u8 *buffer, size_t size,
60 static size_t rng_buffer_size(void)
62 return SMP_CACHE_BYTES < 32 ? 32 : SMP_CACHE_BYTES;
65 static void add_early_randomness(struct hwrng *rng)
68 size_t size = min_t(size_t, 16, rng_buffer_size());
70 mutex_lock(&reading_mutex);
71 bytes_read = rng_get_data(rng, rng_buffer, size, 0);
72 mutex_unlock(&reading_mutex);
74 add_device_randomness(rng_buffer, bytes_read);
77 static inline void cleanup_rng(struct kref *kref)
79 struct hwrng *rng = container_of(kref, struct hwrng, ref);
84 complete(&rng->cleanup_done);
87 static int set_current_rng(struct hwrng *rng)
91 BUG_ON(!mutex_is_locked(&rng_mutex));
93 err = hwrng_init(rng);
103 static void drop_current_rng(void)
105 BUG_ON(!mutex_is_locked(&rng_mutex));
109 /* decrease last reference for triggering the cleanup */
110 kref_put(¤t_rng->ref, cleanup_rng);
114 /* Returns ERR_PTR(), NULL or refcounted hwrng */
115 static struct hwrng *get_current_rng_nolock(void)
118 kref_get(¤t_rng->ref);
123 static struct hwrng *get_current_rng(void)
127 if (mutex_lock_interruptible(&rng_mutex))
128 return ERR_PTR(-ERESTARTSYS);
130 rng = get_current_rng_nolock();
132 mutex_unlock(&rng_mutex);
136 static void put_rng(struct hwrng *rng)
139 * Hold rng_mutex here so we serialize in case they set_current_rng
140 * on rng again immediately.
142 mutex_lock(&rng_mutex);
144 kref_put(&rng->ref, cleanup_rng);
145 mutex_unlock(&rng_mutex);
148 static int hwrng_init(struct hwrng *rng)
150 if (kref_get_unless_zero(&rng->ref))
156 ret = rng->init(rng);
161 kref_init(&rng->ref);
162 reinit_completion(&rng->cleanup_done);
165 current_quality = rng->quality ? : default_quality;
166 if (current_quality > 1024)
167 current_quality = 1024;
169 if (current_quality == 0 && hwrng_fill)
170 kthread_stop(hwrng_fill);
171 if (current_quality > 0 && !hwrng_fill)
177 static int rng_dev_open(struct inode *inode, struct file *filp)
179 /* enforce read-only access to this chrdev */
180 if ((filp->f_mode & FMODE_READ) == 0)
182 if (filp->f_mode & FMODE_WRITE)
187 static inline int rng_get_data(struct hwrng *rng, u8 *buffer, size_t size,
191 BUG_ON(!mutex_is_locked(&reading_mutex));
193 return rng->read(rng, (void *)buffer, size, wait);
195 if (rng->data_present)
196 present = rng->data_present(rng, wait);
201 return rng->data_read(rng, (u32 *)buffer);
206 static ssize_t rng_dev_read(struct file *filp, char __user *buf,
207 size_t size, loff_t *offp)
215 rng = get_current_rng();
225 if (mutex_lock_interruptible(&reading_mutex)) {
230 bytes_read = rng_get_data(rng, rng_buffer,
232 !(filp->f_flags & O_NONBLOCK));
233 if (bytes_read < 0) {
235 goto out_unlock_reading;
237 data_avail = bytes_read;
241 if (filp->f_flags & O_NONBLOCK) {
243 goto out_unlock_reading;
252 if (copy_to_user(buf + ret, rng_buffer + data_avail,
255 goto out_unlock_reading;
262 mutex_unlock(&reading_mutex);
266 schedule_timeout_interruptible(1);
268 if (signal_pending(current)) {
277 mutex_unlock(&reading_mutex);
283 static const struct file_operations rng_chrdev_ops = {
284 .owner = THIS_MODULE,
285 .open = rng_dev_open,
286 .read = rng_dev_read,
287 .llseek = noop_llseek,
290 static const struct attribute_group *rng_dev_groups[];
292 static struct miscdevice rng_miscdev = {
293 .minor = HWRNG_MINOR,
294 .name = RNG_MODULE_NAME,
296 .fops = &rng_chrdev_ops,
297 .groups = rng_dev_groups,
300 static int enable_best_rng(void)
304 BUG_ON(!mutex_is_locked(&rng_mutex));
306 /* rng_list is sorted by quality, use the best (=first) one */
307 if (!list_empty(&rng_list)) {
308 struct hwrng *new_rng;
310 new_rng = list_entry(rng_list.next, struct hwrng, list);
311 ret = ((new_rng == current_rng) ? 0 : set_current_rng(new_rng));
313 cur_rng_set_by_user = 0;
316 cur_rng_set_by_user = 0;
323 static ssize_t hwrng_attr_current_store(struct device *dev,
324 struct device_attribute *attr,
325 const char *buf, size_t len)
328 struct hwrng *rng, *old_rng, *new_rng;
330 err = mutex_lock_interruptible(&rng_mutex);
334 old_rng = current_rng;
335 if (sysfs_streq(buf, "")) {
336 err = enable_best_rng();
338 list_for_each_entry(rng, &rng_list, list) {
339 if (sysfs_streq(rng->name, buf)) {
340 cur_rng_set_by_user = 1;
341 err = set_current_rng(rng);
346 new_rng = get_current_rng_nolock();
347 mutex_unlock(&rng_mutex);
350 if (new_rng != old_rng)
351 add_early_randomness(new_rng);
358 static ssize_t hwrng_attr_current_show(struct device *dev,
359 struct device_attribute *attr,
365 rng = get_current_rng();
369 ret = snprintf(buf, PAGE_SIZE, "%s\n", rng ? rng->name : "none");
375 static ssize_t hwrng_attr_available_show(struct device *dev,
376 struct device_attribute *attr,
382 err = mutex_lock_interruptible(&rng_mutex);
386 list_for_each_entry(rng, &rng_list, list) {
387 strlcat(buf, rng->name, PAGE_SIZE);
388 strlcat(buf, " ", PAGE_SIZE);
390 strlcat(buf, "\n", PAGE_SIZE);
391 mutex_unlock(&rng_mutex);
396 static ssize_t hwrng_attr_selected_show(struct device *dev,
397 struct device_attribute *attr,
400 return snprintf(buf, PAGE_SIZE, "%d\n", cur_rng_set_by_user);
403 static DEVICE_ATTR(rng_current, S_IRUGO | S_IWUSR,
404 hwrng_attr_current_show,
405 hwrng_attr_current_store);
406 static DEVICE_ATTR(rng_available, S_IRUGO,
407 hwrng_attr_available_show,
409 static DEVICE_ATTR(rng_selected, S_IRUGO,
410 hwrng_attr_selected_show,
413 static struct attribute *rng_dev_attrs[] = {
414 &dev_attr_rng_current.attr,
415 &dev_attr_rng_available.attr,
416 &dev_attr_rng_selected.attr,
420 ATTRIBUTE_GROUPS(rng_dev);
422 static void __exit unregister_miscdev(void)
424 misc_deregister(&rng_miscdev);
427 static int __init register_miscdev(void)
429 return misc_register(&rng_miscdev);
432 static int hwrng_fillfn(void *unused)
436 while (!kthread_should_stop()) {
439 rng = get_current_rng();
440 if (IS_ERR(rng) || !rng)
442 mutex_lock(&reading_mutex);
443 rc = rng_get_data(rng, rng_fillbuf,
444 rng_buffer_size(), 1);
445 mutex_unlock(&reading_mutex);
448 pr_warn("hwrng: no data available\n");
449 msleep_interruptible(10000);
452 /* Outside lock, sure, but y'know: randomness. */
453 add_hwgenerator_randomness((void *)rng_fillbuf, rc,
454 rc * current_quality * 8 >> 10);
460 static void start_khwrngd(void)
462 hwrng_fill = kthread_run(hwrng_fillfn, NULL, "hwrng");
463 if (IS_ERR(hwrng_fill)) {
464 pr_err("hwrng_fill thread creation failed\n");
469 int hwrng_register(struct hwrng *rng)
473 struct list_head *rng_list_ptr;
474 bool is_new_current = false;
476 if (!rng->name || (!rng->data_read && !rng->read))
479 mutex_lock(&rng_mutex);
481 /* Must not register two RNGs with the same name. */
483 list_for_each_entry(tmp, &rng_list, list) {
484 if (strcmp(tmp->name, rng->name) == 0)
488 init_completion(&rng->cleanup_done);
489 complete(&rng->cleanup_done);
491 /* rng_list is sorted by decreasing quality */
492 list_for_each(rng_list_ptr, &rng_list) {
493 tmp = list_entry(rng_list_ptr, struct hwrng, list);
494 if (tmp->quality < rng->quality)
497 list_add_tail(&rng->list, rng_list_ptr);
500 (!cur_rng_set_by_user && rng->quality > current_rng->quality)) {
502 * Set new rng as current as the new rng source
503 * provides better entropy quality and was not
504 * chosen by userspace.
506 err = set_current_rng(rng);
509 /* to use current_rng in add_early_randomness() we need
512 is_new_current = true;
515 mutex_unlock(&rng_mutex);
516 if (is_new_current || !rng->init) {
518 * Use a new device's input to add some randomness to
519 * the system. If this rng device isn't going to be
520 * used right away, its init function hasn't been
521 * called yet by set_current_rng(); so only use the
522 * randomness from devices that don't need an init callback
524 add_early_randomness(rng);
530 mutex_unlock(&rng_mutex);
534 EXPORT_SYMBOL_GPL(hwrng_register);
536 void hwrng_unregister(struct hwrng *rng)
538 struct hwrng *old_rng, *new_rng;
541 mutex_lock(&rng_mutex);
543 old_rng = current_rng;
544 list_del(&rng->list);
545 if (current_rng == rng) {
546 err = enable_best_rng();
549 cur_rng_set_by_user = 0;
553 new_rng = get_current_rng_nolock();
554 if (list_empty(&rng_list)) {
555 mutex_unlock(&rng_mutex);
557 kthread_stop(hwrng_fill);
559 mutex_unlock(&rng_mutex);
562 if (old_rng != new_rng)
563 add_early_randomness(new_rng);
567 wait_for_completion(&rng->cleanup_done);
569 EXPORT_SYMBOL_GPL(hwrng_unregister);
571 static void devm_hwrng_release(struct device *dev, void *res)
573 hwrng_unregister(*(struct hwrng **)res);
576 static int devm_hwrng_match(struct device *dev, void *res, void *data)
578 struct hwrng **r = res;
580 if (WARN_ON(!r || !*r))
586 int devm_hwrng_register(struct device *dev, struct hwrng *rng)
591 ptr = devres_alloc(devm_hwrng_release, sizeof(*ptr), GFP_KERNEL);
595 error = hwrng_register(rng);
602 devres_add(dev, ptr);
605 EXPORT_SYMBOL_GPL(devm_hwrng_register);
607 void devm_hwrng_unregister(struct device *dev, struct hwrng *rng)
609 devres_release(dev, devm_hwrng_release, devm_hwrng_match, rng);
611 EXPORT_SYMBOL_GPL(devm_hwrng_unregister);
613 static int __init hwrng_modinit(void)
617 /* kmalloc makes this safe for virt_to_page() in virtio_rng.c */
618 rng_buffer = kmalloc(rng_buffer_size(), GFP_KERNEL);
622 rng_fillbuf = kmalloc(rng_buffer_size(), GFP_KERNEL);
628 ret = register_miscdev();
637 static void __exit hwrng_modexit(void)
639 mutex_lock(&rng_mutex);
643 mutex_unlock(&rng_mutex);
645 unregister_miscdev();
648 module_init(hwrng_modinit);
649 module_exit(hwrng_modexit);
651 MODULE_DESCRIPTION("H/W Random Number Generator (RNG) driver");
652 MODULE_LICENSE("GPL");