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/freezer.h> 17 #include <linux/fs.h> 18 #include <linux/hw_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> 28 29 #define RNG_MODULE_NAME "hw_random" 30 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" */ 45 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"); 52 53 static void drop_current_rng(void); 54 static int hwrng_init(struct hwrng *rng); 55 static void start_khwrngd(void); 56 57 static inline int rng_get_data(struct hwrng *rng, u8 *buffer, size_t size, 58 int wait); 59 60 static size_t rng_buffer_size(void) 61 { 62 return SMP_CACHE_BYTES < 32 ? 32 : SMP_CACHE_BYTES; 63 } 64 65 static void add_early_randomness(struct hwrng *rng) 66 { 67 int bytes_read; 68 size_t size = min_t(size_t, 16, rng_buffer_size()); 69 70 mutex_lock(&reading_mutex); 71 bytes_read = rng_get_data(rng, rng_buffer, size, 0); 72 mutex_unlock(&reading_mutex); 73 if (bytes_read > 0) 74 add_device_randomness(rng_buffer, bytes_read); 75 } 76 77 static inline void cleanup_rng(struct kref *kref) 78 { 79 struct hwrng *rng = container_of(kref, struct hwrng, ref); 80 81 if (rng->cleanup) 82 rng->cleanup(rng); 83 84 complete(&rng->cleanup_done); 85 } 86 87 static int set_current_rng(struct hwrng *rng) 88 { 89 int err; 90 91 BUG_ON(!mutex_is_locked(&rng_mutex)); 92 93 err = hwrng_init(rng); 94 if (err) 95 return err; 96 97 drop_current_rng(); 98 current_rng = rng; 99 100 return 0; 101 } 102 103 static void drop_current_rng(void) 104 { 105 BUG_ON(!mutex_is_locked(&rng_mutex)); 106 if (!current_rng) 107 return; 108 109 /* decrease last reference for triggering the cleanup */ 110 kref_put(¤t_rng->ref, cleanup_rng); 111 current_rng = NULL; 112 } 113 114 /* Returns ERR_PTR(), NULL or refcounted hwrng */ 115 static struct hwrng *get_current_rng_nolock(void) 116 { 117 if (current_rng) 118 kref_get(¤t_rng->ref); 119 120 return current_rng; 121 } 122 123 static struct hwrng *get_current_rng(void) 124 { 125 struct hwrng *rng; 126 127 if (mutex_lock_interruptible(&rng_mutex)) 128 return ERR_PTR(-ERESTARTSYS); 129 130 rng = get_current_rng_nolock(); 131 132 mutex_unlock(&rng_mutex); 133 return rng; 134 } 135 136 static void put_rng(struct hwrng *rng) 137 { 138 /* 139 * Hold rng_mutex here so we serialize in case they set_current_rng 140 * on rng again immediately. 141 */ 142 mutex_lock(&rng_mutex); 143 if (rng) 144 kref_put(&rng->ref, cleanup_rng); 145 mutex_unlock(&rng_mutex); 146 } 147 148 static int hwrng_init(struct hwrng *rng) 149 { 150 if (kref_get_unless_zero(&rng->ref)) 151 goto skip_init; 152 153 if (rng->init) { 154 int ret; 155 156 ret = rng->init(rng); 157 if (ret) 158 return ret; 159 } 160 161 kref_init(&rng->ref); 162 reinit_completion(&rng->cleanup_done); 163 164 skip_init: 165 current_quality = rng->quality ? : default_quality; 166 if (current_quality > 1024) 167 current_quality = 1024; 168 169 if (current_quality == 0 && hwrng_fill) 170 kthread_stop(hwrng_fill); 171 if (current_quality > 0 && !hwrng_fill) 172 start_khwrngd(); 173 174 return 0; 175 } 176 177 static int rng_dev_open(struct inode *inode, struct file *filp) 178 { 179 /* enforce read-only access to this chrdev */ 180 if ((filp->f_mode & FMODE_READ) == 0) 181 return -EINVAL; 182 if (filp->f_mode & FMODE_WRITE) 183 return -EINVAL; 184 return 0; 185 } 186 187 static inline int rng_get_data(struct hwrng *rng, u8 *buffer, size_t size, 188 int wait) { 189 int present; 190 191 BUG_ON(!mutex_is_locked(&reading_mutex)); 192 if (rng->read) 193 return rng->read(rng, (void *)buffer, size, wait); 194 195 if (rng->data_present) 196 present = rng->data_present(rng, wait); 197 else 198 present = 1; 199 200 if (present) 201 return rng->data_read(rng, (u32 *)buffer); 202 203 return 0; 204 } 205 206 static ssize_t rng_dev_read(struct file *filp, char __user *buf, 207 size_t size, loff_t *offp) 208 { 209 ssize_t ret = 0; 210 int err = 0; 211 int bytes_read, len; 212 struct hwrng *rng; 213 214 while (size) { 215 rng = get_current_rng(); 216 if (IS_ERR(rng)) { 217 err = PTR_ERR(rng); 218 goto out; 219 } 220 if (!rng) { 221 err = -ENODEV; 222 goto out; 223 } 224 225 if (mutex_lock_interruptible(&reading_mutex)) { 226 err = -ERESTARTSYS; 227 goto out_put; 228 } 229 if (!data_avail) { 230 bytes_read = rng_get_data(rng, rng_buffer, 231 rng_buffer_size(), 232 !(filp->f_flags & O_NONBLOCK)); 233 if (bytes_read < 0) { 234 err = bytes_read; 235 goto out_unlock_reading; 236 } 237 data_avail = bytes_read; 238 } 239 240 if (!data_avail) { 241 if (filp->f_flags & O_NONBLOCK) { 242 err = -EAGAIN; 243 goto out_unlock_reading; 244 } 245 } else { 246 len = data_avail; 247 if (len > size) 248 len = size; 249 250 data_avail -= len; 251 252 if (copy_to_user(buf + ret, rng_buffer + data_avail, 253 len)) { 254 err = -EFAULT; 255 goto out_unlock_reading; 256 } 257 258 size -= len; 259 ret += len; 260 } 261 262 mutex_unlock(&reading_mutex); 263 put_rng(rng); 264 265 if (need_resched()) 266 schedule_timeout_interruptible(1); 267 268 if (signal_pending(current)) { 269 err = -ERESTARTSYS; 270 goto out; 271 } 272 } 273 out: 274 return ret ? : err; 275 276 out_unlock_reading: 277 mutex_unlock(&reading_mutex); 278 out_put: 279 put_rng(rng); 280 goto out; 281 } 282 283 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, 288 }; 289 290 static const struct attribute_group *rng_dev_groups[]; 291 292 static struct miscdevice rng_miscdev = { 293 .minor = HWRNG_MINOR, 294 .name = RNG_MODULE_NAME, 295 .nodename = "hwrng", 296 .fops = &rng_chrdev_ops, 297 .groups = rng_dev_groups, 298 }; 299 300 static int enable_best_rng(void) 301 { 302 int ret = -ENODEV; 303 304 BUG_ON(!mutex_is_locked(&rng_mutex)); 305 306 /* rng_list is sorted by quality, use the best (=first) one */ 307 if (!list_empty(&rng_list)) { 308 struct hwrng *new_rng; 309 310 new_rng = list_entry(rng_list.next, struct hwrng, list); 311 ret = ((new_rng == current_rng) ? 0 : set_current_rng(new_rng)); 312 if (!ret) 313 cur_rng_set_by_user = 0; 314 } else { 315 drop_current_rng(); 316 cur_rng_set_by_user = 0; 317 ret = 0; 318 } 319 320 return ret; 321 } 322 323 static ssize_t hwrng_attr_current_store(struct device *dev, 324 struct device_attribute *attr, 325 const char *buf, size_t len) 326 { 327 int err = -ENODEV; 328 struct hwrng *rng, *old_rng, *new_rng; 329 330 err = mutex_lock_interruptible(&rng_mutex); 331 if (err) 332 return -ERESTARTSYS; 333 334 old_rng = current_rng; 335 if (sysfs_streq(buf, "")) { 336 err = enable_best_rng(); 337 } else { 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); 342 break; 343 } 344 } 345 } 346 new_rng = get_current_rng_nolock(); 347 mutex_unlock(&rng_mutex); 348 349 if (new_rng) { 350 if (new_rng != old_rng) 351 add_early_randomness(new_rng); 352 put_rng(new_rng); 353 } 354 355 return err ? : len; 356 } 357 358 static ssize_t hwrng_attr_current_show(struct device *dev, 359 struct device_attribute *attr, 360 char *buf) 361 { 362 ssize_t ret; 363 struct hwrng *rng; 364 365 rng = get_current_rng(); 366 if (IS_ERR(rng)) 367 return PTR_ERR(rng); 368 369 ret = snprintf(buf, PAGE_SIZE, "%s\n", rng ? rng->name : "none"); 370 put_rng(rng); 371 372 return ret; 373 } 374 375 static ssize_t hwrng_attr_available_show(struct device *dev, 376 struct device_attribute *attr, 377 char *buf) 378 { 379 int err; 380 struct hwrng *rng; 381 382 err = mutex_lock_interruptible(&rng_mutex); 383 if (err) 384 return -ERESTARTSYS; 385 buf[0] = '\0'; 386 list_for_each_entry(rng, &rng_list, list) { 387 strlcat(buf, rng->name, PAGE_SIZE); 388 strlcat(buf, " ", PAGE_SIZE); 389 } 390 strlcat(buf, "\n", PAGE_SIZE); 391 mutex_unlock(&rng_mutex); 392 393 return strlen(buf); 394 } 395 396 static ssize_t hwrng_attr_selected_show(struct device *dev, 397 struct device_attribute *attr, 398 char *buf) 399 { 400 return snprintf(buf, PAGE_SIZE, "%d\n", cur_rng_set_by_user); 401 } 402 403 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, 408 NULL); 409 static DEVICE_ATTR(rng_selected, S_IRUGO, 410 hwrng_attr_selected_show, 411 NULL); 412 413 static struct attribute *rng_dev_attrs[] = { 414 &dev_attr_rng_current.attr, 415 &dev_attr_rng_available.attr, 416 &dev_attr_rng_selected.attr, 417 NULL 418 }; 419 420 ATTRIBUTE_GROUPS(rng_dev); 421 422 static void __exit unregister_miscdev(void) 423 { 424 misc_deregister(&rng_miscdev); 425 } 426 427 static int __init register_miscdev(void) 428 { 429 return misc_register(&rng_miscdev); 430 } 431 432 static int hwrng_fillfn(void *unused) 433 { 434 long rc; 435 436 set_freezable(); 437 438 while (!kthread_freezable_should_stop(NULL)) { 439 struct hwrng *rng; 440 441 rng = get_current_rng(); 442 if (IS_ERR(rng) || !rng) 443 break; 444 mutex_lock(&reading_mutex); 445 rc = rng_get_data(rng, rng_fillbuf, 446 rng_buffer_size(), 1); 447 mutex_unlock(&reading_mutex); 448 put_rng(rng); 449 if (rc <= 0) { 450 pr_warn("hwrng: no data available\n"); 451 msleep_interruptible(10000); 452 continue; 453 } 454 /* Outside lock, sure, but y'know: randomness. */ 455 add_hwgenerator_randomness((void *)rng_fillbuf, rc, 456 rc * current_quality * 8 >> 10); 457 } 458 hwrng_fill = NULL; 459 return 0; 460 } 461 462 static void start_khwrngd(void) 463 { 464 hwrng_fill = kthread_run(hwrng_fillfn, NULL, "hwrng"); 465 if (IS_ERR(hwrng_fill)) { 466 pr_err("hwrng_fill thread creation failed\n"); 467 hwrng_fill = NULL; 468 } 469 } 470 471 int hwrng_register(struct hwrng *rng) 472 { 473 int err = -EINVAL; 474 struct hwrng *tmp; 475 struct list_head *rng_list_ptr; 476 bool is_new_current = false; 477 478 if (!rng->name || (!rng->data_read && !rng->read)) 479 goto out; 480 481 mutex_lock(&rng_mutex); 482 483 /* Must not register two RNGs with the same name. */ 484 err = -EEXIST; 485 list_for_each_entry(tmp, &rng_list, list) { 486 if (strcmp(tmp->name, rng->name) == 0) 487 goto out_unlock; 488 } 489 490 init_completion(&rng->cleanup_done); 491 complete(&rng->cleanup_done); 492 493 /* rng_list is sorted by decreasing quality */ 494 list_for_each(rng_list_ptr, &rng_list) { 495 tmp = list_entry(rng_list_ptr, struct hwrng, list); 496 if (tmp->quality < rng->quality) 497 break; 498 } 499 list_add_tail(&rng->list, rng_list_ptr); 500 501 if (!current_rng || 502 (!cur_rng_set_by_user && rng->quality > current_rng->quality)) { 503 /* 504 * Set new rng as current as the new rng source 505 * provides better entropy quality and was not 506 * chosen by userspace. 507 */ 508 err = set_current_rng(rng); 509 if (err) 510 goto out_unlock; 511 /* to use current_rng in add_early_randomness() we need 512 * to take a ref 513 */ 514 is_new_current = true; 515 kref_get(&rng->ref); 516 } 517 mutex_unlock(&rng_mutex); 518 if (is_new_current || !rng->init) { 519 /* 520 * Use a new device's input to add some randomness to 521 * the system. If this rng device isn't going to be 522 * used right away, its init function hasn't been 523 * called yet by set_current_rng(); so only use the 524 * randomness from devices that don't need an init callback 525 */ 526 add_early_randomness(rng); 527 } 528 if (is_new_current) 529 put_rng(rng); 530 return 0; 531 out_unlock: 532 mutex_unlock(&rng_mutex); 533 out: 534 return err; 535 } 536 EXPORT_SYMBOL_GPL(hwrng_register); 537 538 void hwrng_unregister(struct hwrng *rng) 539 { 540 struct hwrng *old_rng, *new_rng; 541 int err; 542 543 mutex_lock(&rng_mutex); 544 545 old_rng = current_rng; 546 list_del(&rng->list); 547 if (current_rng == rng) { 548 err = enable_best_rng(); 549 if (err) { 550 drop_current_rng(); 551 cur_rng_set_by_user = 0; 552 } 553 } 554 555 new_rng = get_current_rng_nolock(); 556 if (list_empty(&rng_list)) { 557 mutex_unlock(&rng_mutex); 558 if (hwrng_fill) 559 kthread_stop(hwrng_fill); 560 } else 561 mutex_unlock(&rng_mutex); 562 563 if (new_rng) { 564 if (old_rng != new_rng) 565 add_early_randomness(new_rng); 566 put_rng(new_rng); 567 } 568 569 wait_for_completion(&rng->cleanup_done); 570 } 571 EXPORT_SYMBOL_GPL(hwrng_unregister); 572 573 static void devm_hwrng_release(struct device *dev, void *res) 574 { 575 hwrng_unregister(*(struct hwrng **)res); 576 } 577 578 static int devm_hwrng_match(struct device *dev, void *res, void *data) 579 { 580 struct hwrng **r = res; 581 582 if (WARN_ON(!r || !*r)) 583 return 0; 584 585 return *r == data; 586 } 587 588 int devm_hwrng_register(struct device *dev, struct hwrng *rng) 589 { 590 struct hwrng **ptr; 591 int error; 592 593 ptr = devres_alloc(devm_hwrng_release, sizeof(*ptr), GFP_KERNEL); 594 if (!ptr) 595 return -ENOMEM; 596 597 error = hwrng_register(rng); 598 if (error) { 599 devres_free(ptr); 600 return error; 601 } 602 603 *ptr = rng; 604 devres_add(dev, ptr); 605 return 0; 606 } 607 EXPORT_SYMBOL_GPL(devm_hwrng_register); 608 609 void devm_hwrng_unregister(struct device *dev, struct hwrng *rng) 610 { 611 devres_release(dev, devm_hwrng_release, devm_hwrng_match, rng); 612 } 613 EXPORT_SYMBOL_GPL(devm_hwrng_unregister); 614 615 static int __init hwrng_modinit(void) 616 { 617 int ret = -ENOMEM; 618 619 /* kmalloc makes this safe for virt_to_page() in virtio_rng.c */ 620 rng_buffer = kmalloc(rng_buffer_size(), GFP_KERNEL); 621 if (!rng_buffer) 622 return -ENOMEM; 623 624 rng_fillbuf = kmalloc(rng_buffer_size(), GFP_KERNEL); 625 if (!rng_fillbuf) { 626 kfree(rng_buffer); 627 return -ENOMEM; 628 } 629 630 ret = register_miscdev(); 631 if (ret) { 632 kfree(rng_fillbuf); 633 kfree(rng_buffer); 634 } 635 636 return ret; 637 } 638 639 static void __exit hwrng_modexit(void) 640 { 641 mutex_lock(&rng_mutex); 642 BUG_ON(current_rng); 643 kfree(rng_buffer); 644 kfree(rng_fillbuf); 645 mutex_unlock(&rng_mutex); 646 647 unregister_miscdev(); 648 } 649 650 module_init(hwrng_modinit); 651 module_exit(hwrng_modexit); 652 653 MODULE_DESCRIPTION("H/W Random Number Generator (RNG) driver"); 654 MODULE_LICENSE("GPL"); 655