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/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 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");
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, 0);
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_nolock(void)
117 kref_get(¤t_rng->ref);
122 static struct hwrng *get_current_rng(void)
126 if (mutex_lock_interruptible(&rng_mutex))
127 return ERR_PTR(-ERESTARTSYS);
129 rng = get_current_rng_nolock();
131 mutex_unlock(&rng_mutex);
135 static void put_rng(struct hwrng *rng)
138 * Hold rng_mutex here so we serialize in case they set_current_rng
139 * on rng again immediately.
141 mutex_lock(&rng_mutex);
143 kref_put(&rng->ref, cleanup_rng);
144 mutex_unlock(&rng_mutex);
147 static int hwrng_init(struct hwrng *rng)
149 if (kref_get_unless_zero(&rng->ref))
155 ret = rng->init(rng);
160 kref_init(&rng->ref);
161 reinit_completion(&rng->cleanup_done);
164 current_quality = rng->quality ? : default_quality;
165 if (current_quality > 1024)
166 current_quality = 1024;
168 if (current_quality == 0 && hwrng_fill)
169 kthread_stop(hwrng_fill);
170 if (current_quality > 0 && !hwrng_fill)
176 static int rng_dev_open(struct inode *inode, struct file *filp)
178 /* enforce read-only access to this chrdev */
179 if ((filp->f_mode & FMODE_READ) == 0)
181 if (filp->f_mode & FMODE_WRITE)
186 static inline int rng_get_data(struct hwrng *rng, u8 *buffer, size_t size,
190 BUG_ON(!mutex_is_locked(&reading_mutex));
192 return rng->read(rng, (void *)buffer, size, wait);
194 if (rng->data_present)
195 present = rng->data_present(rng, wait);
200 return rng->data_read(rng, (u32 *)buffer);
205 static ssize_t rng_dev_read(struct file *filp, char __user *buf,
206 size_t size, loff_t *offp)
214 rng = get_current_rng();
224 if (mutex_lock_interruptible(&reading_mutex)) {
229 bytes_read = rng_get_data(rng, rng_buffer,
231 !(filp->f_flags & O_NONBLOCK));
232 if (bytes_read < 0) {
234 goto out_unlock_reading;
236 data_avail = bytes_read;
240 if (filp->f_flags & O_NONBLOCK) {
242 goto out_unlock_reading;
251 if (copy_to_user(buf + ret, rng_buffer + data_avail,
254 goto out_unlock_reading;
261 mutex_unlock(&reading_mutex);
265 schedule_timeout_interruptible(1);
267 if (signal_pending(current)) {
276 mutex_unlock(&reading_mutex);
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,
289 static const struct attribute_group *rng_dev_groups[];
291 static struct miscdevice rng_miscdev = {
292 .minor = HWRNG_MINOR,
293 .name = RNG_MODULE_NAME,
295 .fops = &rng_chrdev_ops,
296 .groups = rng_dev_groups,
299 static int enable_best_rng(void)
303 BUG_ON(!mutex_is_locked(&rng_mutex));
305 /* rng_list is sorted by quality, use the best (=first) one */
306 if (!list_empty(&rng_list)) {
307 struct hwrng *new_rng;
309 new_rng = list_entry(rng_list.next, struct hwrng, list);
310 ret = ((new_rng == current_rng) ? 0 : set_current_rng(new_rng));
312 cur_rng_set_by_user = 0;
315 cur_rng_set_by_user = 0;
322 static ssize_t hwrng_attr_current_store(struct device *dev,
323 struct device_attribute *attr,
324 const char *buf, size_t len)
327 struct hwrng *rng, *old_rng, *new_rng;
329 err = mutex_lock_interruptible(&rng_mutex);
333 old_rng = current_rng;
334 if (sysfs_streq(buf, "")) {
335 err = enable_best_rng();
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);
345 new_rng = get_current_rng_nolock();
346 mutex_unlock(&rng_mutex);
349 if (new_rng != old_rng)
350 add_early_randomness(new_rng);
357 static ssize_t hwrng_attr_current_show(struct device *dev,
358 struct device_attribute *attr,
364 rng = get_current_rng();
368 ret = snprintf(buf, PAGE_SIZE, "%s\n", rng ? rng->name : "none");
374 static ssize_t hwrng_attr_available_show(struct device *dev,
375 struct device_attribute *attr,
381 err = mutex_lock_interruptible(&rng_mutex);
385 list_for_each_entry(rng, &rng_list, list) {
386 strlcat(buf, rng->name, PAGE_SIZE);
387 strlcat(buf, " ", PAGE_SIZE);
389 strlcat(buf, "\n", PAGE_SIZE);
390 mutex_unlock(&rng_mutex);
395 static ssize_t hwrng_attr_selected_show(struct device *dev,
396 struct device_attribute *attr,
399 return snprintf(buf, PAGE_SIZE, "%d\n", cur_rng_set_by_user);
402 static DEVICE_ATTR(rng_current, S_IRUGO | S_IWUSR,
403 hwrng_attr_current_show,
404 hwrng_attr_current_store);
405 static DEVICE_ATTR(rng_available, S_IRUGO,
406 hwrng_attr_available_show,
408 static DEVICE_ATTR(rng_selected, S_IRUGO,
409 hwrng_attr_selected_show,
412 static struct attribute *rng_dev_attrs[] = {
413 &dev_attr_rng_current.attr,
414 &dev_attr_rng_available.attr,
415 &dev_attr_rng_selected.attr,
419 ATTRIBUTE_GROUPS(rng_dev);
421 static void __exit unregister_miscdev(void)
423 misc_deregister(&rng_miscdev);
426 static int __init register_miscdev(void)
428 return misc_register(&rng_miscdev);
431 static int hwrng_fillfn(void *unused)
435 while (!kthread_should_stop()) {
438 rng = get_current_rng();
439 if (IS_ERR(rng) || !rng)
441 mutex_lock(&reading_mutex);
442 rc = rng_get_data(rng, rng_fillbuf,
443 rng_buffer_size(), 1);
444 mutex_unlock(&reading_mutex);
447 pr_warn("hwrng: no data available\n");
448 msleep_interruptible(10000);
451 /* Outside lock, sure, but y'know: randomness. */
452 add_hwgenerator_randomness((void *)rng_fillbuf, rc,
453 rc * current_quality * 8 >> 10);
459 static void start_khwrngd(void)
461 hwrng_fill = kthread_run(hwrng_fillfn, NULL, "hwrng");
462 if (IS_ERR(hwrng_fill)) {
463 pr_err("hwrng_fill thread creation failed\n");
468 int hwrng_register(struct hwrng *rng)
472 struct list_head *rng_list_ptr;
473 bool is_new_current = false;
475 if (!rng->name || (!rng->data_read && !rng->read))
478 mutex_lock(&rng_mutex);
480 /* Must not register two RNGs with the same name. */
482 list_for_each_entry(tmp, &rng_list, list) {
483 if (strcmp(tmp->name, rng->name) == 0)
487 init_completion(&rng->cleanup_done);
488 complete(&rng->cleanup_done);
490 /* rng_list is sorted by decreasing quality */
491 list_for_each(rng_list_ptr, &rng_list) {
492 tmp = list_entry(rng_list_ptr, struct hwrng, list);
493 if (tmp->quality < rng->quality)
496 list_add_tail(&rng->list, rng_list_ptr);
499 (!cur_rng_set_by_user && rng->quality > current_rng->quality)) {
501 * Set new rng as current as the new rng source
502 * provides better entropy quality and was not
503 * chosen by userspace.
505 err = set_current_rng(rng);
508 /* to use current_rng in add_early_randomness() we need
511 is_new_current = true;
514 mutex_unlock(&rng_mutex);
515 if (is_new_current || !rng->init) {
517 * Use a new device's input to add some randomness to
518 * the system. If this rng device isn't going to be
519 * used right away, its init function hasn't been
520 * called yet by set_current_rng(); so only use the
521 * randomness from devices that don't need an init callback
523 add_early_randomness(rng);
529 mutex_unlock(&rng_mutex);
533 EXPORT_SYMBOL_GPL(hwrng_register);
535 void hwrng_unregister(struct hwrng *rng)
537 struct hwrng *old_rng, *new_rng;
540 mutex_lock(&rng_mutex);
542 old_rng = current_rng;
543 list_del(&rng->list);
544 if (current_rng == rng) {
545 err = enable_best_rng();
548 cur_rng_set_by_user = 0;
552 new_rng = get_current_rng_nolock();
553 if (list_empty(&rng_list)) {
554 mutex_unlock(&rng_mutex);
556 kthread_stop(hwrng_fill);
558 mutex_unlock(&rng_mutex);
561 if (old_rng != new_rng)
562 add_early_randomness(new_rng);
566 wait_for_completion(&rng->cleanup_done);
568 EXPORT_SYMBOL_GPL(hwrng_unregister);
570 static void devm_hwrng_release(struct device *dev, void *res)
572 hwrng_unregister(*(struct hwrng **)res);
575 static int devm_hwrng_match(struct device *dev, void *res, void *data)
577 struct hwrng **r = res;
579 if (WARN_ON(!r || !*r))
585 int devm_hwrng_register(struct device *dev, struct hwrng *rng)
590 ptr = devres_alloc(devm_hwrng_release, sizeof(*ptr), GFP_KERNEL);
594 error = hwrng_register(rng);
601 devres_add(dev, ptr);
604 EXPORT_SYMBOL_GPL(devm_hwrng_register);
606 void devm_hwrng_unregister(struct device *dev, struct hwrng *rng)
608 devres_release(dev, devm_hwrng_release, devm_hwrng_match, rng);
610 EXPORT_SYMBOL_GPL(devm_hwrng_unregister);
612 static int __init hwrng_modinit(void)
616 /* kmalloc makes this safe for virt_to_page() in virtio_rng.c */
617 rng_buffer = kmalloc(rng_buffer_size(), GFP_KERNEL);
621 rng_fillbuf = kmalloc(rng_buffer_size(), GFP_KERNEL);
627 ret = register_miscdev();
636 static void __exit hwrng_modexit(void)
638 mutex_lock(&rng_mutex);
642 mutex_unlock(&rng_mutex);
644 unregister_miscdev();
647 module_init(hwrng_modinit);
648 module_exit(hwrng_modexit);
650 MODULE_DESCRIPTION("H/W Random Number Generator (RNG) driver");
651 MODULE_LICENSE("GPL");