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/fs.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> 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 */ 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 -- obsolete, use rng_quality instead"); 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 hwrng_manage_rngd(struct hwrng *rng); 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 69 mutex_lock(&reading_mutex); 70 bytes_read = rng_get_data(rng, rng_fillbuf, 32, 0); 71 mutex_unlock(&reading_mutex); 72 if (bytes_read > 0) 73 add_device_randomness(rng_fillbuf, bytes_read); 74 } 75 76 static inline void cleanup_rng(struct kref *kref) 77 { 78 struct hwrng *rng = container_of(kref, struct hwrng, ref); 79 80 if (rng->cleanup) 81 rng->cleanup(rng); 82 83 complete(&rng->cleanup_done); 84 } 85 86 static int set_current_rng(struct hwrng *rng) 87 { 88 int err; 89 90 BUG_ON(!mutex_is_locked(&rng_mutex)); 91 92 err = hwrng_init(rng); 93 if (err) 94 return err; 95 96 drop_current_rng(); 97 current_rng = rng; 98 99 return 0; 100 } 101 102 static void drop_current_rng(void) 103 { 104 BUG_ON(!mutex_is_locked(&rng_mutex)); 105 if (!current_rng) 106 return; 107 108 /* decrease last reference for triggering the cleanup */ 109 kref_put(¤t_rng->ref, cleanup_rng); 110 current_rng = NULL; 111 } 112 113 /* Returns ERR_PTR(), NULL or refcounted hwrng */ 114 static struct hwrng *get_current_rng_nolock(void) 115 { 116 if (current_rng) 117 kref_get(¤t_rng->ref); 118 119 return current_rng; 120 } 121 122 static struct hwrng *get_current_rng(void) 123 { 124 struct hwrng *rng; 125 126 if (mutex_lock_interruptible(&rng_mutex)) 127 return ERR_PTR(-ERESTARTSYS); 128 129 rng = get_current_rng_nolock(); 130 131 mutex_unlock(&rng_mutex); 132 return rng; 133 } 134 135 static void put_rng(struct hwrng *rng) 136 { 137 /* 138 * Hold rng_mutex here so we serialize in case they set_current_rng 139 * on rng again immediately. 140 */ 141 mutex_lock(&rng_mutex); 142 if (rng) 143 kref_put(&rng->ref, cleanup_rng); 144 mutex_unlock(&rng_mutex); 145 } 146 147 static int hwrng_init(struct hwrng *rng) 148 { 149 if (kref_get_unless_zero(&rng->ref)) 150 goto skip_init; 151 152 if (rng->init) { 153 int ret; 154 155 ret = rng->init(rng); 156 if (ret) 157 return ret; 158 } 159 160 kref_init(&rng->ref); 161 reinit_completion(&rng->cleanup_done); 162 163 skip_init: 164 if (!rng->quality) 165 rng->quality = default_quality; 166 if (rng->quality > 1024) 167 rng->quality = 1024; 168 current_quality = rng->quality; /* obsolete */ 169 170 hwrng_manage_rngd(rng); 171 172 return 0; 173 } 174 175 static int rng_dev_open(struct inode *inode, struct file *filp) 176 { 177 /* enforce read-only access to this chrdev */ 178 if ((filp->f_mode & FMODE_READ) == 0) 179 return -EINVAL; 180 if (filp->f_mode & FMODE_WRITE) 181 return -EINVAL; 182 return 0; 183 } 184 185 static inline int rng_get_data(struct hwrng *rng, u8 *buffer, size_t size, 186 int wait) { 187 int present; 188 189 BUG_ON(!mutex_is_locked(&reading_mutex)); 190 if (rng->read) 191 return rng->read(rng, (void *)buffer, size, wait); 192 193 if (rng->data_present) 194 present = rng->data_present(rng, wait); 195 else 196 present = 1; 197 198 if (present) 199 return rng->data_read(rng, (u32 *)buffer); 200 201 return 0; 202 } 203 204 static ssize_t rng_dev_read(struct file *filp, char __user *buf, 205 size_t size, loff_t *offp) 206 { 207 ssize_t ret = 0; 208 int err = 0; 209 int bytes_read, len; 210 struct hwrng *rng; 211 212 while (size) { 213 rng = get_current_rng(); 214 if (IS_ERR(rng)) { 215 err = PTR_ERR(rng); 216 goto out; 217 } 218 if (!rng) { 219 err = -ENODEV; 220 goto out; 221 } 222 223 if (mutex_lock_interruptible(&reading_mutex)) { 224 err = -ERESTARTSYS; 225 goto out_put; 226 } 227 if (!data_avail) { 228 bytes_read = rng_get_data(rng, rng_buffer, 229 rng_buffer_size(), 230 !(filp->f_flags & O_NONBLOCK)); 231 if (bytes_read < 0) { 232 err = bytes_read; 233 goto out_unlock_reading; 234 } 235 data_avail = bytes_read; 236 } 237 238 if (!data_avail) { 239 if (filp->f_flags & O_NONBLOCK) { 240 err = -EAGAIN; 241 goto out_unlock_reading; 242 } 243 } else { 244 len = data_avail; 245 if (len > size) 246 len = size; 247 248 data_avail -= len; 249 250 if (copy_to_user(buf + ret, rng_buffer + data_avail, 251 len)) { 252 err = -EFAULT; 253 goto out_unlock_reading; 254 } 255 256 size -= len; 257 ret += len; 258 } 259 260 mutex_unlock(&reading_mutex); 261 put_rng(rng); 262 263 if (need_resched()) 264 schedule_timeout_interruptible(1); 265 266 if (signal_pending(current)) { 267 err = -ERESTARTSYS; 268 goto out; 269 } 270 } 271 out: 272 return ret ? : err; 273 274 out_unlock_reading: 275 mutex_unlock(&reading_mutex); 276 out_put: 277 put_rng(rng); 278 goto out; 279 } 280 281 static const struct file_operations rng_chrdev_ops = { 282 .owner = THIS_MODULE, 283 .open = rng_dev_open, 284 .read = rng_dev_read, 285 .llseek = noop_llseek, 286 }; 287 288 static const struct attribute_group *rng_dev_groups[]; 289 290 static struct miscdevice rng_miscdev = { 291 .minor = HWRNG_MINOR, 292 .name = RNG_MODULE_NAME, 293 .nodename = "hwrng", 294 .fops = &rng_chrdev_ops, 295 .groups = rng_dev_groups, 296 }; 297 298 static int enable_best_rng(void) 299 { 300 struct hwrng *rng, *new_rng = NULL; 301 int ret = -ENODEV; 302 303 BUG_ON(!mutex_is_locked(&rng_mutex)); 304 305 /* no rng to use? */ 306 if (list_empty(&rng_list)) { 307 drop_current_rng(); 308 cur_rng_set_by_user = 0; 309 return 0; 310 } 311 312 /* use the rng which offers the best quality */ 313 list_for_each_entry(rng, &rng_list, list) { 314 if (!new_rng || rng->quality > new_rng->quality) 315 new_rng = rng; 316 } 317 318 ret = ((new_rng == current_rng) ? 0 : set_current_rng(new_rng)); 319 if (!ret) 320 cur_rng_set_by_user = 0; 321 322 return ret; 323 } 324 325 static ssize_t rng_current_store(struct device *dev, 326 struct device_attribute *attr, 327 const char *buf, size_t len) 328 { 329 int err; 330 struct hwrng *rng, *old_rng, *new_rng; 331 332 err = mutex_lock_interruptible(&rng_mutex); 333 if (err) 334 return -ERESTARTSYS; 335 336 old_rng = current_rng; 337 if (sysfs_streq(buf, "")) { 338 err = enable_best_rng(); 339 } else { 340 list_for_each_entry(rng, &rng_list, list) { 341 if (sysfs_streq(rng->name, buf)) { 342 err = set_current_rng(rng); 343 if (!err) 344 cur_rng_set_by_user = 1; 345 break; 346 } 347 } 348 } 349 new_rng = get_current_rng_nolock(); 350 mutex_unlock(&rng_mutex); 351 352 if (new_rng) { 353 if (new_rng != old_rng) 354 add_early_randomness(new_rng); 355 put_rng(new_rng); 356 } 357 358 return err ? : len; 359 } 360 361 static ssize_t rng_current_show(struct device *dev, 362 struct device_attribute *attr, 363 char *buf) 364 { 365 ssize_t ret; 366 struct hwrng *rng; 367 368 rng = get_current_rng(); 369 if (IS_ERR(rng)) 370 return PTR_ERR(rng); 371 372 ret = snprintf(buf, PAGE_SIZE, "%s\n", rng ? rng->name : "none"); 373 put_rng(rng); 374 375 return ret; 376 } 377 378 static ssize_t rng_available_show(struct device *dev, 379 struct device_attribute *attr, 380 char *buf) 381 { 382 int err; 383 struct hwrng *rng; 384 385 err = mutex_lock_interruptible(&rng_mutex); 386 if (err) 387 return -ERESTARTSYS; 388 buf[0] = '\0'; 389 list_for_each_entry(rng, &rng_list, list) { 390 strlcat(buf, rng->name, PAGE_SIZE); 391 strlcat(buf, " ", PAGE_SIZE); 392 } 393 strlcat(buf, "\n", PAGE_SIZE); 394 mutex_unlock(&rng_mutex); 395 396 return strlen(buf); 397 } 398 399 static ssize_t rng_selected_show(struct device *dev, 400 struct device_attribute *attr, 401 char *buf) 402 { 403 return sysfs_emit(buf, "%d\n", cur_rng_set_by_user); 404 } 405 406 static ssize_t rng_quality_show(struct device *dev, 407 struct device_attribute *attr, 408 char *buf) 409 { 410 ssize_t ret; 411 struct hwrng *rng; 412 413 rng = get_current_rng(); 414 if (IS_ERR(rng)) 415 return PTR_ERR(rng); 416 417 if (!rng) /* no need to put_rng */ 418 return -ENODEV; 419 420 ret = sysfs_emit(buf, "%hu\n", rng->quality); 421 put_rng(rng); 422 423 return ret; 424 } 425 426 static ssize_t rng_quality_store(struct device *dev, 427 struct device_attribute *attr, 428 const char *buf, size_t len) 429 { 430 u16 quality; 431 int ret = -EINVAL; 432 433 if (len < 2) 434 return -EINVAL; 435 436 ret = mutex_lock_interruptible(&rng_mutex); 437 if (ret) 438 return -ERESTARTSYS; 439 440 ret = kstrtou16(buf, 0, &quality); 441 if (ret || quality > 1024) { 442 ret = -EINVAL; 443 goto out; 444 } 445 446 if (!current_rng) { 447 ret = -ENODEV; 448 goto out; 449 } 450 451 current_rng->quality = quality; 452 current_quality = quality; /* obsolete */ 453 454 /* the best available RNG may have changed */ 455 ret = enable_best_rng(); 456 457 /* start/stop rngd if necessary */ 458 if (current_rng) 459 hwrng_manage_rngd(current_rng); 460 461 out: 462 mutex_unlock(&rng_mutex); 463 return ret ? ret : len; 464 } 465 466 static DEVICE_ATTR_RW(rng_current); 467 static DEVICE_ATTR_RO(rng_available); 468 static DEVICE_ATTR_RO(rng_selected); 469 static DEVICE_ATTR_RW(rng_quality); 470 471 static struct attribute *rng_dev_attrs[] = { 472 &dev_attr_rng_current.attr, 473 &dev_attr_rng_available.attr, 474 &dev_attr_rng_selected.attr, 475 &dev_attr_rng_quality.attr, 476 NULL 477 }; 478 479 ATTRIBUTE_GROUPS(rng_dev); 480 481 static void __exit unregister_miscdev(void) 482 { 483 misc_deregister(&rng_miscdev); 484 } 485 486 static int __init register_miscdev(void) 487 { 488 return misc_register(&rng_miscdev); 489 } 490 491 static int hwrng_fillfn(void *unused) 492 { 493 size_t entropy, entropy_credit = 0; /* in 1/1024 of a bit */ 494 long rc; 495 496 while (!kthread_should_stop()) { 497 unsigned short quality; 498 struct hwrng *rng; 499 500 rng = get_current_rng(); 501 if (IS_ERR(rng) || !rng) 502 break; 503 mutex_lock(&reading_mutex); 504 rc = rng_get_data(rng, rng_fillbuf, 505 rng_buffer_size(), 1); 506 if (current_quality != rng->quality) 507 rng->quality = current_quality; /* obsolete */ 508 quality = rng->quality; 509 mutex_unlock(&reading_mutex); 510 put_rng(rng); 511 512 if (!quality) 513 break; 514 515 if (rc <= 0) { 516 pr_warn("hwrng: no data available\n"); 517 msleep_interruptible(10000); 518 continue; 519 } 520 521 /* If we cannot credit at least one bit of entropy, 522 * keep track of the remainder for the next iteration 523 */ 524 entropy = rc * quality * 8 + entropy_credit; 525 if ((entropy >> 10) == 0) 526 entropy_credit = entropy; 527 528 /* Outside lock, sure, but y'know: randomness. */ 529 add_hwgenerator_randomness((void *)rng_fillbuf, rc, 530 entropy >> 10); 531 } 532 hwrng_fill = NULL; 533 return 0; 534 } 535 536 static void hwrng_manage_rngd(struct hwrng *rng) 537 { 538 if (WARN_ON(!mutex_is_locked(&rng_mutex))) 539 return; 540 541 if (rng->quality == 0 && hwrng_fill) 542 kthread_stop(hwrng_fill); 543 if (rng->quality > 0 && !hwrng_fill) { 544 hwrng_fill = kthread_run(hwrng_fillfn, NULL, "hwrng"); 545 if (IS_ERR(hwrng_fill)) { 546 pr_err("hwrng_fill thread creation failed\n"); 547 hwrng_fill = NULL; 548 } 549 } 550 } 551 552 int hwrng_register(struct hwrng *rng) 553 { 554 int err = -EINVAL; 555 struct hwrng *tmp; 556 bool is_new_current = false; 557 558 if (!rng->name || (!rng->data_read && !rng->read)) 559 goto out; 560 561 mutex_lock(&rng_mutex); 562 563 /* Must not register two RNGs with the same name. */ 564 err = -EEXIST; 565 list_for_each_entry(tmp, &rng_list, list) { 566 if (strcmp(tmp->name, rng->name) == 0) 567 goto out_unlock; 568 } 569 list_add_tail(&rng->list, &rng_list); 570 571 init_completion(&rng->cleanup_done); 572 complete(&rng->cleanup_done); 573 574 if (!current_rng || 575 (!cur_rng_set_by_user && rng->quality > current_rng->quality)) { 576 /* 577 * Set new rng as current as the new rng source 578 * provides better entropy quality and was not 579 * chosen by userspace. 580 */ 581 err = set_current_rng(rng); 582 if (err) 583 goto out_unlock; 584 /* to use current_rng in add_early_randomness() we need 585 * to take a ref 586 */ 587 is_new_current = true; 588 kref_get(&rng->ref); 589 } 590 mutex_unlock(&rng_mutex); 591 if (is_new_current || !rng->init) { 592 /* 593 * Use a new device's input to add some randomness to 594 * the system. If this rng device isn't going to be 595 * used right away, its init function hasn't been 596 * called yet by set_current_rng(); so only use the 597 * randomness from devices that don't need an init callback 598 */ 599 add_early_randomness(rng); 600 } 601 if (is_new_current) 602 put_rng(rng); 603 return 0; 604 out_unlock: 605 mutex_unlock(&rng_mutex); 606 out: 607 return err; 608 } 609 EXPORT_SYMBOL_GPL(hwrng_register); 610 611 void hwrng_unregister(struct hwrng *rng) 612 { 613 struct hwrng *old_rng, *new_rng; 614 int err; 615 616 mutex_lock(&rng_mutex); 617 618 old_rng = current_rng; 619 list_del(&rng->list); 620 if (current_rng == rng) { 621 err = enable_best_rng(); 622 if (err) { 623 drop_current_rng(); 624 cur_rng_set_by_user = 0; 625 } 626 } 627 628 new_rng = get_current_rng_nolock(); 629 if (list_empty(&rng_list)) { 630 mutex_unlock(&rng_mutex); 631 if (hwrng_fill) 632 kthread_stop(hwrng_fill); 633 } else 634 mutex_unlock(&rng_mutex); 635 636 if (new_rng) { 637 if (old_rng != new_rng) 638 add_early_randomness(new_rng); 639 put_rng(new_rng); 640 } 641 642 wait_for_completion(&rng->cleanup_done); 643 } 644 EXPORT_SYMBOL_GPL(hwrng_unregister); 645 646 static void devm_hwrng_release(struct device *dev, void *res) 647 { 648 hwrng_unregister(*(struct hwrng **)res); 649 } 650 651 static int devm_hwrng_match(struct device *dev, void *res, void *data) 652 { 653 struct hwrng **r = res; 654 655 if (WARN_ON(!r || !*r)) 656 return 0; 657 658 return *r == data; 659 } 660 661 int devm_hwrng_register(struct device *dev, struct hwrng *rng) 662 { 663 struct hwrng **ptr; 664 int error; 665 666 ptr = devres_alloc(devm_hwrng_release, sizeof(*ptr), GFP_KERNEL); 667 if (!ptr) 668 return -ENOMEM; 669 670 error = hwrng_register(rng); 671 if (error) { 672 devres_free(ptr); 673 return error; 674 } 675 676 *ptr = rng; 677 devres_add(dev, ptr); 678 return 0; 679 } 680 EXPORT_SYMBOL_GPL(devm_hwrng_register); 681 682 void devm_hwrng_unregister(struct device *dev, struct hwrng *rng) 683 { 684 devres_release(dev, devm_hwrng_release, devm_hwrng_match, rng); 685 } 686 EXPORT_SYMBOL_GPL(devm_hwrng_unregister); 687 688 static int __init hwrng_modinit(void) 689 { 690 int ret; 691 692 /* kmalloc makes this safe for virt_to_page() in virtio_rng.c */ 693 rng_buffer = kmalloc(rng_buffer_size(), GFP_KERNEL); 694 if (!rng_buffer) 695 return -ENOMEM; 696 697 rng_fillbuf = kmalloc(rng_buffer_size(), GFP_KERNEL); 698 if (!rng_fillbuf) { 699 kfree(rng_buffer); 700 return -ENOMEM; 701 } 702 703 ret = register_miscdev(); 704 if (ret) { 705 kfree(rng_fillbuf); 706 kfree(rng_buffer); 707 } 708 709 return ret; 710 } 711 712 static void __exit hwrng_modexit(void) 713 { 714 mutex_lock(&rng_mutex); 715 BUG_ON(current_rng); 716 kfree(rng_buffer); 717 kfree(rng_fillbuf); 718 mutex_unlock(&rng_mutex); 719 720 unregister_miscdev(); 721 } 722 723 fs_initcall(hwrng_modinit); /* depends on misc_register() */ 724 module_exit(hwrng_modexit); 725 726 MODULE_DESCRIPTION("H/W Random Number Generator (RNG) driver"); 727 MODULE_LICENSE("GPL"); 728