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/hw_random.txt 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/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>
28 #define RNG_MODULE_NAME "hw_random"
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" */
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");
52 static void drop_current_rng(void);
53 static int hwrng_init(struct hwrng *rng);
54 static void start_khwrngd(void);
56 static inline int rng_get_data(struct hwrng *rng, u8 *buffer, size_t size,
59 static size_t rng_buffer_size(void)
61 return SMP_CACHE_BYTES < 32 ? 32 : SMP_CACHE_BYTES;
64 static void add_early_randomness(struct hwrng *rng)
67 size_t size = min_t(size_t, 16, rng_buffer_size());
69 mutex_lock(&reading_mutex);
70 bytes_read = rng_get_data(rng, rng_buffer, size, 1);
71 mutex_unlock(&reading_mutex);
73 add_device_randomness(rng_buffer, bytes_read);
76 static inline void cleanup_rng(struct kref *kref)
78 struct hwrng *rng = container_of(kref, struct hwrng, ref);
83 complete(&rng->cleanup_done);
86 static int set_current_rng(struct hwrng *rng)
90 BUG_ON(!mutex_is_locked(&rng_mutex));
92 err = hwrng_init(rng);
102 static void drop_current_rng(void)
104 BUG_ON(!mutex_is_locked(&rng_mutex));
108 /* decrease last reference for triggering the cleanup */
109 kref_put(¤t_rng->ref, cleanup_rng);
113 /* Returns ERR_PTR(), NULL or refcounted hwrng */
114 static struct hwrng *get_current_rng(void)
118 if (mutex_lock_interruptible(&rng_mutex))
119 return ERR_PTR(-ERESTARTSYS);
125 mutex_unlock(&rng_mutex);
129 static void put_rng(struct hwrng *rng)
132 * Hold rng_mutex here so we serialize in case they set_current_rng
133 * on rng again immediately.
135 mutex_lock(&rng_mutex);
137 kref_put(&rng->ref, cleanup_rng);
138 mutex_unlock(&rng_mutex);
141 static int hwrng_init(struct hwrng *rng)
143 if (kref_get_unless_zero(&rng->ref))
149 ret = rng->init(rng);
154 kref_init(&rng->ref);
155 reinit_completion(&rng->cleanup_done);
158 add_early_randomness(rng);
160 current_quality = rng->quality ? : default_quality;
161 if (current_quality > 1024)
162 current_quality = 1024;
164 if (current_quality == 0 && hwrng_fill)
165 kthread_stop(hwrng_fill);
166 if (current_quality > 0 && !hwrng_fill)
172 static int rng_dev_open(struct inode *inode, struct file *filp)
174 /* enforce read-only access to this chrdev */
175 if ((filp->f_mode & FMODE_READ) == 0)
177 if (filp->f_mode & FMODE_WRITE)
182 static inline int rng_get_data(struct hwrng *rng, u8 *buffer, size_t size,
186 BUG_ON(!mutex_is_locked(&reading_mutex));
188 return rng->read(rng, (void *)buffer, size, wait);
190 if (rng->data_present)
191 present = rng->data_present(rng, wait);
196 return rng->data_read(rng, (u32 *)buffer);
201 static ssize_t rng_dev_read(struct file *filp, char __user *buf,
202 size_t size, loff_t *offp)
210 rng = get_current_rng();
220 if (mutex_lock_interruptible(&reading_mutex)) {
225 bytes_read = rng_get_data(rng, rng_buffer,
227 !(filp->f_flags & O_NONBLOCK));
228 if (bytes_read < 0) {
230 goto out_unlock_reading;
232 data_avail = bytes_read;
236 if (filp->f_flags & O_NONBLOCK) {
238 goto out_unlock_reading;
247 if (copy_to_user(buf + ret, rng_buffer + data_avail,
250 goto out_unlock_reading;
257 mutex_unlock(&reading_mutex);
261 schedule_timeout_interruptible(1);
263 if (signal_pending(current)) {
272 mutex_unlock(&reading_mutex);
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,
285 static const struct attribute_group *rng_dev_groups[];
287 static struct miscdevice rng_miscdev = {
288 .minor = HWRNG_MINOR,
289 .name = RNG_MODULE_NAME,
291 .fops = &rng_chrdev_ops,
292 .groups = rng_dev_groups,
295 static int enable_best_rng(void)
299 BUG_ON(!mutex_is_locked(&rng_mutex));
301 /* rng_list is sorted by quality, use the best (=first) one */
302 if (!list_empty(&rng_list)) {
303 struct hwrng *new_rng;
305 new_rng = list_entry(rng_list.next, struct hwrng, list);
306 ret = ((new_rng == current_rng) ? 0 : set_current_rng(new_rng));
308 cur_rng_set_by_user = 0;
311 cur_rng_set_by_user = 0;
318 static ssize_t hwrng_attr_current_store(struct device *dev,
319 struct device_attribute *attr,
320 const char *buf, size_t len)
325 err = mutex_lock_interruptible(&rng_mutex);
329 if (sysfs_streq(buf, "")) {
330 err = enable_best_rng();
332 list_for_each_entry(rng, &rng_list, list) {
333 if (sysfs_streq(rng->name, buf)) {
334 cur_rng_set_by_user = 1;
335 err = set_current_rng(rng);
341 mutex_unlock(&rng_mutex);
346 static ssize_t hwrng_attr_current_show(struct device *dev,
347 struct device_attribute *attr,
353 rng = get_current_rng();
357 ret = snprintf(buf, PAGE_SIZE, "%s\n", rng ? rng->name : "none");
363 static ssize_t hwrng_attr_available_show(struct device *dev,
364 struct device_attribute *attr,
370 err = mutex_lock_interruptible(&rng_mutex);
374 list_for_each_entry(rng, &rng_list, list) {
375 strlcat(buf, rng->name, PAGE_SIZE);
376 strlcat(buf, " ", PAGE_SIZE);
378 strlcat(buf, "\n", PAGE_SIZE);
379 mutex_unlock(&rng_mutex);
384 static ssize_t hwrng_attr_selected_show(struct device *dev,
385 struct device_attribute *attr,
388 return snprintf(buf, PAGE_SIZE, "%d\n", cur_rng_set_by_user);
391 static DEVICE_ATTR(rng_current, S_IRUGO | S_IWUSR,
392 hwrng_attr_current_show,
393 hwrng_attr_current_store);
394 static DEVICE_ATTR(rng_available, S_IRUGO,
395 hwrng_attr_available_show,
397 static DEVICE_ATTR(rng_selected, S_IRUGO,
398 hwrng_attr_selected_show,
401 static struct attribute *rng_dev_attrs[] = {
402 &dev_attr_rng_current.attr,
403 &dev_attr_rng_available.attr,
404 &dev_attr_rng_selected.attr,
408 ATTRIBUTE_GROUPS(rng_dev);
410 static void __exit unregister_miscdev(void)
412 misc_deregister(&rng_miscdev);
415 static int __init register_miscdev(void)
417 return misc_register(&rng_miscdev);
420 static int hwrng_fillfn(void *unused)
424 while (!kthread_should_stop()) {
427 rng = get_current_rng();
428 if (IS_ERR(rng) || !rng)
430 mutex_lock(&reading_mutex);
431 rc = rng_get_data(rng, rng_fillbuf,
432 rng_buffer_size(), 1);
433 mutex_unlock(&reading_mutex);
436 pr_warn("hwrng: no data available\n");
437 msleep_interruptible(10000);
440 /* Outside lock, sure, but y'know: randomness. */
441 add_hwgenerator_randomness((void *)rng_fillbuf, rc,
442 rc * current_quality * 8 >> 10);
448 static void start_khwrngd(void)
450 hwrng_fill = kthread_run(hwrng_fillfn, NULL, "hwrng");
451 if (IS_ERR(hwrng_fill)) {
452 pr_err("hwrng_fill thread creation failed\n");
457 int hwrng_register(struct hwrng *rng)
460 struct hwrng *old_rng, *tmp;
461 struct list_head *rng_list_ptr;
463 if (!rng->name || (!rng->data_read && !rng->read))
466 mutex_lock(&rng_mutex);
467 /* Must not register two RNGs with the same name. */
469 list_for_each_entry(tmp, &rng_list, list) {
470 if (strcmp(tmp->name, rng->name) == 0)
474 init_completion(&rng->cleanup_done);
475 complete(&rng->cleanup_done);
477 /* rng_list is sorted by decreasing quality */
478 list_for_each(rng_list_ptr, &rng_list) {
479 tmp = list_entry(rng_list_ptr, struct hwrng, list);
480 if (tmp->quality < rng->quality)
483 list_add_tail(&rng->list, rng_list_ptr);
485 old_rng = current_rng;
488 (!cur_rng_set_by_user && rng->quality > old_rng->quality)) {
490 * Set new rng as current as the new rng source
491 * provides better entropy quality and was not
492 * chosen by userspace.
494 err = set_current_rng(rng);
499 if (old_rng && !rng->init) {
501 * Use a new device's input to add some randomness to
502 * the system. If this rng device isn't going to be
503 * used right away, its init function hasn't been
504 * called yet; so only use the randomness from devices
505 * that don't need an init callback.
507 add_early_randomness(rng);
511 mutex_unlock(&rng_mutex);
515 EXPORT_SYMBOL_GPL(hwrng_register);
517 void hwrng_unregister(struct hwrng *rng)
521 mutex_lock(&rng_mutex);
523 list_del(&rng->list);
524 if (current_rng == rng) {
525 err = enable_best_rng();
528 cur_rng_set_by_user = 0;
532 if (list_empty(&rng_list)) {
533 mutex_unlock(&rng_mutex);
535 kthread_stop(hwrng_fill);
537 mutex_unlock(&rng_mutex);
539 wait_for_completion(&rng->cleanup_done);
541 EXPORT_SYMBOL_GPL(hwrng_unregister);
543 static void devm_hwrng_release(struct device *dev, void *res)
545 hwrng_unregister(*(struct hwrng **)res);
548 static int devm_hwrng_match(struct device *dev, void *res, void *data)
550 struct hwrng **r = res;
552 if (WARN_ON(!r || !*r))
558 int devm_hwrng_register(struct device *dev, struct hwrng *rng)
563 ptr = devres_alloc(devm_hwrng_release, sizeof(*ptr), GFP_KERNEL);
567 error = hwrng_register(rng);
574 devres_add(dev, ptr);
577 EXPORT_SYMBOL_GPL(devm_hwrng_register);
579 void devm_hwrng_unregister(struct device *dev, struct hwrng *rng)
581 devres_release(dev, devm_hwrng_release, devm_hwrng_match, rng);
583 EXPORT_SYMBOL_GPL(devm_hwrng_unregister);
585 static int __init hwrng_modinit(void)
589 /* kmalloc makes this safe for virt_to_page() in virtio_rng.c */
590 rng_buffer = kmalloc(rng_buffer_size(), GFP_KERNEL);
594 rng_fillbuf = kmalloc(rng_buffer_size(), GFP_KERNEL);
600 ret = register_miscdev();
609 static void __exit hwrng_modexit(void)
611 mutex_lock(&rng_mutex);
615 mutex_unlock(&rng_mutex);
617 unregister_miscdev();
620 module_init(hwrng_modinit);
621 module_exit(hwrng_modexit);
623 MODULE_DESCRIPTION("H/W Random Number Generator (RNG) driver");
624 MODULE_LICENSE("GPL");