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/kernel.h> 19 #include <linux/kthread.h> 20 #include <linux/miscdevice.h> 21 #include <linux/module.h> 22 #include <linux/random.h> 23 #include <linux/sched.h> 24 #include <linux/sched/signal.h> 25 #include <linux/slab.h> 26 #include <linux/string.h> 27 #include <linux/uaccess.h> 28 29 #define RNG_MODULE_NAME "hw_random" 30 31 #define RNG_BUFFER_SIZE (SMP_CACHE_BYTES < 32 ? 32 : SMP_CACHE_BYTES) 32 33 static struct hwrng *current_rng; 34 /* the current rng has been explicitly chosen by user via sysfs */ 35 static int cur_rng_set_by_user; 36 static struct task_struct *hwrng_fill; 37 /* list of registered rngs */ 38 static LIST_HEAD(rng_list); 39 /* Protects rng_list and current_rng */ 40 static DEFINE_MUTEX(rng_mutex); 41 /* Protects rng read functions, data_avail, rng_buffer and rng_fillbuf */ 42 static DEFINE_MUTEX(reading_mutex); 43 static int data_avail; 44 static u8 *rng_buffer, *rng_fillbuf; 45 static unsigned short current_quality; 46 static unsigned short default_quality = 1024; /* default to maximum */ 47 48 module_param(current_quality, ushort, 0644); 49 MODULE_PARM_DESC(current_quality, 50 "current hwrng entropy estimation per 1024 bits of input -- obsolete, use rng_quality instead"); 51 module_param(default_quality, ushort, 0644); 52 MODULE_PARM_DESC(default_quality, 53 "default maximum entropy content of hwrng per 1024 bits of input"); 54 55 static void drop_current_rng(void); 56 static int hwrng_init(struct hwrng *rng); 57 static int hwrng_fillfn(void *unused); 58 59 static inline int rng_get_data(struct hwrng *rng, u8 *buffer, size_t size, 60 int wait); 61 62 static size_t rng_buffer_size(void) 63 { 64 return RNG_BUFFER_SIZE; 65 } 66 67 static inline void cleanup_rng(struct kref *kref) 68 { 69 struct hwrng *rng = container_of(kref, struct hwrng, ref); 70 71 if (rng->cleanup) 72 rng->cleanup(rng); 73 74 complete(&rng->cleanup_done); 75 } 76 77 static int set_current_rng(struct hwrng *rng) 78 { 79 int err; 80 81 BUG_ON(!mutex_is_locked(&rng_mutex)); 82 83 err = hwrng_init(rng); 84 if (err) 85 return err; 86 87 drop_current_rng(); 88 current_rng = rng; 89 90 /* if necessary, start hwrng thread */ 91 if (!hwrng_fill) { 92 hwrng_fill = kthread_run(hwrng_fillfn, NULL, "hwrng"); 93 if (IS_ERR(hwrng_fill)) { 94 pr_err("hwrng_fill thread creation failed\n"); 95 hwrng_fill = NULL; 96 } 97 } 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 current_quality = rng->quality; /* obsolete */ 165 166 return 0; 167 } 168 169 static int rng_dev_open(struct inode *inode, struct file *filp) 170 { 171 /* enforce read-only access to this chrdev */ 172 if ((filp->f_mode & FMODE_READ) == 0) 173 return -EINVAL; 174 if (filp->f_mode & FMODE_WRITE) 175 return -EINVAL; 176 return 0; 177 } 178 179 static inline int rng_get_data(struct hwrng *rng, u8 *buffer, size_t size, 180 int wait) { 181 int present; 182 183 BUG_ON(!mutex_is_locked(&reading_mutex)); 184 if (rng->read) { 185 int err; 186 187 err = rng->read(rng, buffer, size, wait); 188 if (WARN_ON_ONCE(err > 0 && err > size)) 189 err = size; 190 191 return err; 192 } 193 194 if (rng->data_present) 195 present = rng->data_present(rng, wait); 196 else 197 present = 1; 198 199 if (present) 200 return rng->data_read(rng, (u32 *)buffer); 201 202 return 0; 203 } 204 205 static ssize_t rng_dev_read(struct file *filp, char __user *buf, 206 size_t size, loff_t *offp) 207 { 208 u8 buffer[RNG_BUFFER_SIZE]; 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 } else if (bytes_read == 0 && 237 (filp->f_flags & O_NONBLOCK)) { 238 err = -EAGAIN; 239 goto out_unlock_reading; 240 } 241 242 data_avail = bytes_read; 243 } 244 245 len = data_avail; 246 if (len) { 247 if (len > size) 248 len = size; 249 250 data_avail -= len; 251 252 memcpy(buffer, rng_buffer + data_avail, len); 253 } 254 mutex_unlock(&reading_mutex); 255 put_rng(rng); 256 257 if (len) { 258 if (copy_to_user(buf + ret, buffer, len)) { 259 err = -EFAULT; 260 goto out; 261 } 262 263 size -= len; 264 ret += len; 265 } 266 267 268 if (need_resched()) 269 schedule_timeout_interruptible(1); 270 271 if (signal_pending(current)) { 272 err = -ERESTARTSYS; 273 goto out; 274 } 275 } 276 out: 277 memzero_explicit(buffer, sizeof(buffer)); 278 return ret ? : err; 279 280 out_unlock_reading: 281 mutex_unlock(&reading_mutex); 282 out_put: 283 put_rng(rng); 284 goto out; 285 } 286 287 static const struct file_operations rng_chrdev_ops = { 288 .owner = THIS_MODULE, 289 .open = rng_dev_open, 290 .read = rng_dev_read, 291 .llseek = noop_llseek, 292 }; 293 294 static const struct attribute_group *rng_dev_groups[]; 295 296 static struct miscdevice rng_miscdev = { 297 .minor = HWRNG_MINOR, 298 .name = RNG_MODULE_NAME, 299 .nodename = "hwrng", 300 .fops = &rng_chrdev_ops, 301 .groups = rng_dev_groups, 302 }; 303 304 static int enable_best_rng(void) 305 { 306 struct hwrng *rng, *new_rng = NULL; 307 int ret = -ENODEV; 308 309 BUG_ON(!mutex_is_locked(&rng_mutex)); 310 311 /* no rng to use? */ 312 if (list_empty(&rng_list)) { 313 drop_current_rng(); 314 cur_rng_set_by_user = 0; 315 return 0; 316 } 317 318 /* use the rng which offers the best quality */ 319 list_for_each_entry(rng, &rng_list, list) { 320 if (!new_rng || rng->quality > new_rng->quality) 321 new_rng = rng; 322 } 323 324 ret = ((new_rng == current_rng) ? 0 : set_current_rng(new_rng)); 325 if (!ret) 326 cur_rng_set_by_user = 0; 327 328 return ret; 329 } 330 331 static ssize_t rng_current_store(struct device *dev, 332 struct device_attribute *attr, 333 const char *buf, size_t len) 334 { 335 int err; 336 struct hwrng *rng, *new_rng; 337 338 err = mutex_lock_interruptible(&rng_mutex); 339 if (err) 340 return -ERESTARTSYS; 341 342 if (sysfs_streq(buf, "")) { 343 err = enable_best_rng(); 344 } else { 345 list_for_each_entry(rng, &rng_list, list) { 346 if (sysfs_streq(rng->name, buf)) { 347 err = set_current_rng(rng); 348 if (!err) 349 cur_rng_set_by_user = 1; 350 break; 351 } 352 } 353 } 354 new_rng = get_current_rng_nolock(); 355 mutex_unlock(&rng_mutex); 356 357 if (new_rng) 358 put_rng(new_rng); 359 360 return err ? : len; 361 } 362 363 static ssize_t rng_current_show(struct device *dev, 364 struct device_attribute *attr, 365 char *buf) 366 { 367 ssize_t ret; 368 struct hwrng *rng; 369 370 rng = get_current_rng(); 371 if (IS_ERR(rng)) 372 return PTR_ERR(rng); 373 374 ret = sysfs_emit(buf, "%s\n", rng ? rng->name : "none"); 375 put_rng(rng); 376 377 return ret; 378 } 379 380 static ssize_t rng_available_show(struct device *dev, 381 struct device_attribute *attr, 382 char *buf) 383 { 384 int err; 385 struct hwrng *rng; 386 387 err = mutex_lock_interruptible(&rng_mutex); 388 if (err) 389 return -ERESTARTSYS; 390 buf[0] = '\0'; 391 list_for_each_entry(rng, &rng_list, list) { 392 strlcat(buf, rng->name, PAGE_SIZE); 393 strlcat(buf, " ", PAGE_SIZE); 394 } 395 strlcat(buf, "\n", PAGE_SIZE); 396 mutex_unlock(&rng_mutex); 397 398 return strlen(buf); 399 } 400 401 static ssize_t rng_selected_show(struct device *dev, 402 struct device_attribute *attr, 403 char *buf) 404 { 405 return sysfs_emit(buf, "%d\n", cur_rng_set_by_user); 406 } 407 408 static ssize_t rng_quality_show(struct device *dev, 409 struct device_attribute *attr, 410 char *buf) 411 { 412 ssize_t ret; 413 struct hwrng *rng; 414 415 rng = get_current_rng(); 416 if (IS_ERR(rng)) 417 return PTR_ERR(rng); 418 419 if (!rng) /* no need to put_rng */ 420 return -ENODEV; 421 422 ret = sysfs_emit(buf, "%hu\n", rng->quality); 423 put_rng(rng); 424 425 return ret; 426 } 427 428 static ssize_t rng_quality_store(struct device *dev, 429 struct device_attribute *attr, 430 const char *buf, size_t len) 431 { 432 u16 quality; 433 int ret = -EINVAL; 434 435 if (len < 2) 436 return -EINVAL; 437 438 ret = mutex_lock_interruptible(&rng_mutex); 439 if (ret) 440 return -ERESTARTSYS; 441 442 ret = kstrtou16(buf, 0, &quality); 443 if (ret || quality > 1024) { 444 ret = -EINVAL; 445 goto out; 446 } 447 448 if (!current_rng) { 449 ret = -ENODEV; 450 goto out; 451 } 452 453 current_rng->quality = quality; 454 current_quality = quality; /* obsolete */ 455 456 /* the best available RNG may have changed */ 457 ret = enable_best_rng(); 458 459 out: 460 mutex_unlock(&rng_mutex); 461 return ret ? ret : len; 462 } 463 464 static DEVICE_ATTR_RW(rng_current); 465 static DEVICE_ATTR_RO(rng_available); 466 static DEVICE_ATTR_RO(rng_selected); 467 static DEVICE_ATTR_RW(rng_quality); 468 469 static struct attribute *rng_dev_attrs[] = { 470 &dev_attr_rng_current.attr, 471 &dev_attr_rng_available.attr, 472 &dev_attr_rng_selected.attr, 473 &dev_attr_rng_quality.attr, 474 NULL 475 }; 476 477 ATTRIBUTE_GROUPS(rng_dev); 478 479 static int hwrng_fillfn(void *unused) 480 { 481 size_t entropy, entropy_credit = 0; /* in 1/1024 of a bit */ 482 long rc; 483 484 while (!kthread_should_stop()) { 485 unsigned short quality; 486 struct hwrng *rng; 487 488 rng = get_current_rng(); 489 if (IS_ERR(rng) || !rng) 490 break; 491 mutex_lock(&reading_mutex); 492 rc = rng_get_data(rng, rng_fillbuf, 493 rng_buffer_size(), 1); 494 if (current_quality != rng->quality) 495 rng->quality = current_quality; /* obsolete */ 496 quality = rng->quality; 497 mutex_unlock(&reading_mutex); 498 499 if (rc <= 0) 500 hwrng_msleep(rng, 10000); 501 502 put_rng(rng); 503 504 if (rc <= 0) 505 continue; 506 507 /* If we cannot credit at least one bit of entropy, 508 * keep track of the remainder for the next iteration 509 */ 510 entropy = rc * quality * 8 + entropy_credit; 511 if ((entropy >> 10) == 0) 512 entropy_credit = entropy; 513 514 /* Outside lock, sure, but y'know: randomness. */ 515 add_hwgenerator_randomness((void *)rng_fillbuf, rc, 516 entropy >> 10, true); 517 } 518 hwrng_fill = NULL; 519 return 0; 520 } 521 522 int hwrng_register(struct hwrng *rng) 523 { 524 int err = -EINVAL; 525 struct hwrng *tmp; 526 527 if (!rng->name || (!rng->data_read && !rng->read)) 528 goto out; 529 530 mutex_lock(&rng_mutex); 531 532 /* Must not register two RNGs with the same name. */ 533 err = -EEXIST; 534 list_for_each_entry(tmp, &rng_list, list) { 535 if (strcmp(tmp->name, rng->name) == 0) 536 goto out_unlock; 537 } 538 list_add_tail(&rng->list, &rng_list); 539 540 init_completion(&rng->cleanup_done); 541 complete(&rng->cleanup_done); 542 init_completion(&rng->dying); 543 544 /* Adjust quality field to always have a proper value */ 545 rng->quality = min_t(u16, min_t(u16, default_quality, 1024), rng->quality ?: 1024); 546 547 if (!current_rng || 548 (!cur_rng_set_by_user && rng->quality > current_rng->quality)) { 549 /* 550 * Set new rng as current as the new rng source 551 * provides better entropy quality and was not 552 * chosen by userspace. 553 */ 554 err = set_current_rng(rng); 555 if (err) 556 goto out_unlock; 557 } 558 mutex_unlock(&rng_mutex); 559 return 0; 560 out_unlock: 561 mutex_unlock(&rng_mutex); 562 out: 563 return err; 564 } 565 EXPORT_SYMBOL_GPL(hwrng_register); 566 567 void hwrng_unregister(struct hwrng *rng) 568 { 569 struct hwrng *new_rng; 570 int err; 571 572 mutex_lock(&rng_mutex); 573 574 list_del(&rng->list); 575 complete_all(&rng->dying); 576 if (current_rng == rng) { 577 err = enable_best_rng(); 578 if (err) { 579 drop_current_rng(); 580 cur_rng_set_by_user = 0; 581 } 582 } 583 584 new_rng = get_current_rng_nolock(); 585 if (list_empty(&rng_list)) { 586 mutex_unlock(&rng_mutex); 587 if (hwrng_fill) 588 kthread_stop(hwrng_fill); 589 } else 590 mutex_unlock(&rng_mutex); 591 592 if (new_rng) 593 put_rng(new_rng); 594 595 wait_for_completion(&rng->cleanup_done); 596 } 597 EXPORT_SYMBOL_GPL(hwrng_unregister); 598 599 static void devm_hwrng_release(struct device *dev, void *res) 600 { 601 hwrng_unregister(*(struct hwrng **)res); 602 } 603 604 static int devm_hwrng_match(struct device *dev, void *res, void *data) 605 { 606 struct hwrng **r = res; 607 608 if (WARN_ON(!r || !*r)) 609 return 0; 610 611 return *r == data; 612 } 613 614 int devm_hwrng_register(struct device *dev, struct hwrng *rng) 615 { 616 struct hwrng **ptr; 617 int error; 618 619 ptr = devres_alloc(devm_hwrng_release, sizeof(*ptr), GFP_KERNEL); 620 if (!ptr) 621 return -ENOMEM; 622 623 error = hwrng_register(rng); 624 if (error) { 625 devres_free(ptr); 626 return error; 627 } 628 629 *ptr = rng; 630 devres_add(dev, ptr); 631 return 0; 632 } 633 EXPORT_SYMBOL_GPL(devm_hwrng_register); 634 635 void devm_hwrng_unregister(struct device *dev, struct hwrng *rng) 636 { 637 devres_release(dev, devm_hwrng_release, devm_hwrng_match, rng); 638 } 639 EXPORT_SYMBOL_GPL(devm_hwrng_unregister); 640 641 long hwrng_msleep(struct hwrng *rng, unsigned int msecs) 642 { 643 unsigned long timeout = msecs_to_jiffies(msecs) + 1; 644 645 return wait_for_completion_interruptible_timeout(&rng->dying, timeout); 646 } 647 EXPORT_SYMBOL_GPL(hwrng_msleep); 648 649 long hwrng_yield(struct hwrng *rng) 650 { 651 return wait_for_completion_interruptible_timeout(&rng->dying, 1); 652 } 653 EXPORT_SYMBOL_GPL(hwrng_yield); 654 655 static int __init hwrng_modinit(void) 656 { 657 int ret; 658 659 /* kmalloc makes this safe for virt_to_page() in virtio_rng.c */ 660 rng_buffer = kmalloc(rng_buffer_size(), GFP_KERNEL); 661 if (!rng_buffer) 662 return -ENOMEM; 663 664 rng_fillbuf = kmalloc(rng_buffer_size(), GFP_KERNEL); 665 if (!rng_fillbuf) { 666 kfree(rng_buffer); 667 return -ENOMEM; 668 } 669 670 ret = misc_register(&rng_miscdev); 671 if (ret) { 672 kfree(rng_fillbuf); 673 kfree(rng_buffer); 674 } 675 676 return ret; 677 } 678 679 static void __exit hwrng_modexit(void) 680 { 681 mutex_lock(&rng_mutex); 682 BUG_ON(current_rng); 683 kfree(rng_buffer); 684 kfree(rng_fillbuf); 685 mutex_unlock(&rng_mutex); 686 687 misc_deregister(&rng_miscdev); 688 } 689 690 fs_initcall(hwrng_modinit); /* depends on misc_register() */ 691 module_exit(hwrng_modexit); 692 693 MODULE_DESCRIPTION("H/W Random Number Generator (RNG) driver"); 694 MODULE_LICENSE("GPL"); 695