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 return rng->read(rng, (void *)buffer, size, wait); 186 187 if (rng->data_present) 188 present = rng->data_present(rng, wait); 189 else 190 present = 1; 191 192 if (present) 193 return rng->data_read(rng, (u32 *)buffer); 194 195 return 0; 196 } 197 198 static ssize_t rng_dev_read(struct file *filp, char __user *buf, 199 size_t size, loff_t *offp) 200 { 201 u8 buffer[RNG_BUFFER_SIZE]; 202 ssize_t ret = 0; 203 int err = 0; 204 int bytes_read, len; 205 struct hwrng *rng; 206 207 while (size) { 208 rng = get_current_rng(); 209 if (IS_ERR(rng)) { 210 err = PTR_ERR(rng); 211 goto out; 212 } 213 if (!rng) { 214 err = -ENODEV; 215 goto out; 216 } 217 218 if (mutex_lock_interruptible(&reading_mutex)) { 219 err = -ERESTARTSYS; 220 goto out_put; 221 } 222 if (!data_avail) { 223 bytes_read = rng_get_data(rng, rng_buffer, 224 rng_buffer_size(), 225 !(filp->f_flags & O_NONBLOCK)); 226 if (bytes_read < 0) { 227 err = bytes_read; 228 goto out_unlock_reading; 229 } else if (bytes_read == 0 && 230 (filp->f_flags & O_NONBLOCK)) { 231 err = -EAGAIN; 232 goto out_unlock_reading; 233 } 234 235 data_avail = bytes_read; 236 } 237 238 len = data_avail; 239 if (len) { 240 if (len > size) 241 len = size; 242 243 data_avail -= len; 244 245 memcpy(buffer, rng_buffer + data_avail, len); 246 } 247 mutex_unlock(&reading_mutex); 248 put_rng(rng); 249 250 if (len) { 251 if (copy_to_user(buf + ret, buffer, len)) { 252 err = -EFAULT; 253 goto out; 254 } 255 256 size -= len; 257 ret += len; 258 } 259 260 261 if (need_resched()) 262 schedule_timeout_interruptible(1); 263 264 if (signal_pending(current)) { 265 err = -ERESTARTSYS; 266 goto out; 267 } 268 } 269 out: 270 memzero_explicit(buffer, sizeof(buffer)); 271 return ret ? : err; 272 273 out_unlock_reading: 274 mutex_unlock(&reading_mutex); 275 out_put: 276 put_rng(rng); 277 goto out; 278 } 279 280 static const struct file_operations rng_chrdev_ops = { 281 .owner = THIS_MODULE, 282 .open = rng_dev_open, 283 .read = rng_dev_read, 284 .llseek = noop_llseek, 285 }; 286 287 static const struct attribute_group *rng_dev_groups[]; 288 289 static struct miscdevice rng_miscdev = { 290 .minor = HWRNG_MINOR, 291 .name = RNG_MODULE_NAME, 292 .nodename = "hwrng", 293 .fops = &rng_chrdev_ops, 294 .groups = rng_dev_groups, 295 }; 296 297 static int enable_best_rng(void) 298 { 299 struct hwrng *rng, *new_rng = NULL; 300 int ret = -ENODEV; 301 302 BUG_ON(!mutex_is_locked(&rng_mutex)); 303 304 /* no rng to use? */ 305 if (list_empty(&rng_list)) { 306 drop_current_rng(); 307 cur_rng_set_by_user = 0; 308 return 0; 309 } 310 311 /* use the rng which offers the best quality */ 312 list_for_each_entry(rng, &rng_list, list) { 313 if (!new_rng || rng->quality > new_rng->quality) 314 new_rng = rng; 315 } 316 317 ret = ((new_rng == current_rng) ? 0 : set_current_rng(new_rng)); 318 if (!ret) 319 cur_rng_set_by_user = 0; 320 321 return ret; 322 } 323 324 static ssize_t rng_current_store(struct device *dev, 325 struct device_attribute *attr, 326 const char *buf, size_t len) 327 { 328 int err; 329 struct hwrng *rng, *new_rng; 330 331 err = mutex_lock_interruptible(&rng_mutex); 332 if (err) 333 return -ERESTARTSYS; 334 335 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 err = set_current_rng(rng); 341 if (!err) 342 cur_rng_set_by_user = 1; 343 break; 344 } 345 } 346 } 347 new_rng = get_current_rng_nolock(); 348 mutex_unlock(&rng_mutex); 349 350 if (new_rng) 351 put_rng(new_rng); 352 353 return err ? : len; 354 } 355 356 static ssize_t rng_current_show(struct device *dev, 357 struct device_attribute *attr, 358 char *buf) 359 { 360 ssize_t ret; 361 struct hwrng *rng; 362 363 rng = get_current_rng(); 364 if (IS_ERR(rng)) 365 return PTR_ERR(rng); 366 367 ret = sysfs_emit(buf, "%s\n", rng ? rng->name : "none"); 368 put_rng(rng); 369 370 return ret; 371 } 372 373 static ssize_t rng_available_show(struct device *dev, 374 struct device_attribute *attr, 375 char *buf) 376 { 377 int err; 378 struct hwrng *rng; 379 380 err = mutex_lock_interruptible(&rng_mutex); 381 if (err) 382 return -ERESTARTSYS; 383 buf[0] = '\0'; 384 list_for_each_entry(rng, &rng_list, list) { 385 strlcat(buf, rng->name, PAGE_SIZE); 386 strlcat(buf, " ", PAGE_SIZE); 387 } 388 strlcat(buf, "\n", PAGE_SIZE); 389 mutex_unlock(&rng_mutex); 390 391 return strlen(buf); 392 } 393 394 static ssize_t rng_selected_show(struct device *dev, 395 struct device_attribute *attr, 396 char *buf) 397 { 398 return sysfs_emit(buf, "%d\n", cur_rng_set_by_user); 399 } 400 401 static ssize_t rng_quality_show(struct device *dev, 402 struct device_attribute *attr, 403 char *buf) 404 { 405 ssize_t ret; 406 struct hwrng *rng; 407 408 rng = get_current_rng(); 409 if (IS_ERR(rng)) 410 return PTR_ERR(rng); 411 412 if (!rng) /* no need to put_rng */ 413 return -ENODEV; 414 415 ret = sysfs_emit(buf, "%hu\n", rng->quality); 416 put_rng(rng); 417 418 return ret; 419 } 420 421 static ssize_t rng_quality_store(struct device *dev, 422 struct device_attribute *attr, 423 const char *buf, size_t len) 424 { 425 u16 quality; 426 int ret = -EINVAL; 427 428 if (len < 2) 429 return -EINVAL; 430 431 ret = mutex_lock_interruptible(&rng_mutex); 432 if (ret) 433 return -ERESTARTSYS; 434 435 ret = kstrtou16(buf, 0, &quality); 436 if (ret || quality > 1024) { 437 ret = -EINVAL; 438 goto out; 439 } 440 441 if (!current_rng) { 442 ret = -ENODEV; 443 goto out; 444 } 445 446 current_rng->quality = quality; 447 current_quality = quality; /* obsolete */ 448 449 /* the best available RNG may have changed */ 450 ret = enable_best_rng(); 451 452 out: 453 mutex_unlock(&rng_mutex); 454 return ret ? ret : len; 455 } 456 457 static DEVICE_ATTR_RW(rng_current); 458 static DEVICE_ATTR_RO(rng_available); 459 static DEVICE_ATTR_RO(rng_selected); 460 static DEVICE_ATTR_RW(rng_quality); 461 462 static struct attribute *rng_dev_attrs[] = { 463 &dev_attr_rng_current.attr, 464 &dev_attr_rng_available.attr, 465 &dev_attr_rng_selected.attr, 466 &dev_attr_rng_quality.attr, 467 NULL 468 }; 469 470 ATTRIBUTE_GROUPS(rng_dev); 471 472 static int hwrng_fillfn(void *unused) 473 { 474 size_t entropy, entropy_credit = 0; /* in 1/1024 of a bit */ 475 long rc; 476 477 while (!kthread_should_stop()) { 478 unsigned short quality; 479 struct hwrng *rng; 480 481 rng = get_current_rng(); 482 if (IS_ERR(rng) || !rng) 483 break; 484 mutex_lock(&reading_mutex); 485 rc = rng_get_data(rng, rng_fillbuf, 486 rng_buffer_size(), 1); 487 if (current_quality != rng->quality) 488 rng->quality = current_quality; /* obsolete */ 489 quality = rng->quality; 490 mutex_unlock(&reading_mutex); 491 492 if (rc <= 0) 493 hwrng_msleep(rng, 10000); 494 495 put_rng(rng); 496 497 if (rc <= 0) 498 continue; 499 500 /* If we cannot credit at least one bit of entropy, 501 * keep track of the remainder for the next iteration 502 */ 503 entropy = rc * quality * 8 + entropy_credit; 504 if ((entropy >> 10) == 0) 505 entropy_credit = entropy; 506 507 /* Outside lock, sure, but y'know: randomness. */ 508 add_hwgenerator_randomness((void *)rng_fillbuf, rc, 509 entropy >> 10, true); 510 } 511 hwrng_fill = NULL; 512 return 0; 513 } 514 515 int hwrng_register(struct hwrng *rng) 516 { 517 int err = -EINVAL; 518 struct hwrng *tmp; 519 520 if (!rng->name || (!rng->data_read && !rng->read)) 521 goto out; 522 523 mutex_lock(&rng_mutex); 524 525 /* Must not register two RNGs with the same name. */ 526 err = -EEXIST; 527 list_for_each_entry(tmp, &rng_list, list) { 528 if (strcmp(tmp->name, rng->name) == 0) 529 goto out_unlock; 530 } 531 list_add_tail(&rng->list, &rng_list); 532 533 init_completion(&rng->cleanup_done); 534 complete(&rng->cleanup_done); 535 init_completion(&rng->dying); 536 537 /* Adjust quality field to always have a proper value */ 538 rng->quality = min_t(u16, min_t(u16, default_quality, 1024), rng->quality ?: 1024); 539 540 if (!current_rng || 541 (!cur_rng_set_by_user && rng->quality > current_rng->quality)) { 542 /* 543 * Set new rng as current as the new rng source 544 * provides better entropy quality and was not 545 * chosen by userspace. 546 */ 547 err = set_current_rng(rng); 548 if (err) 549 goto out_unlock; 550 } 551 mutex_unlock(&rng_mutex); 552 return 0; 553 out_unlock: 554 mutex_unlock(&rng_mutex); 555 out: 556 return err; 557 } 558 EXPORT_SYMBOL_GPL(hwrng_register); 559 560 void hwrng_unregister(struct hwrng *rng) 561 { 562 struct hwrng *new_rng; 563 int err; 564 565 mutex_lock(&rng_mutex); 566 567 list_del(&rng->list); 568 complete_all(&rng->dying); 569 if (current_rng == rng) { 570 err = enable_best_rng(); 571 if (err) { 572 drop_current_rng(); 573 cur_rng_set_by_user = 0; 574 } 575 } 576 577 new_rng = get_current_rng_nolock(); 578 if (list_empty(&rng_list)) { 579 mutex_unlock(&rng_mutex); 580 if (hwrng_fill) 581 kthread_stop(hwrng_fill); 582 } else 583 mutex_unlock(&rng_mutex); 584 585 if (new_rng) 586 put_rng(new_rng); 587 588 wait_for_completion(&rng->cleanup_done); 589 } 590 EXPORT_SYMBOL_GPL(hwrng_unregister); 591 592 static void devm_hwrng_release(struct device *dev, void *res) 593 { 594 hwrng_unregister(*(struct hwrng **)res); 595 } 596 597 static int devm_hwrng_match(struct device *dev, void *res, void *data) 598 { 599 struct hwrng **r = res; 600 601 if (WARN_ON(!r || !*r)) 602 return 0; 603 604 return *r == data; 605 } 606 607 int devm_hwrng_register(struct device *dev, struct hwrng *rng) 608 { 609 struct hwrng **ptr; 610 int error; 611 612 ptr = devres_alloc(devm_hwrng_release, sizeof(*ptr), GFP_KERNEL); 613 if (!ptr) 614 return -ENOMEM; 615 616 error = hwrng_register(rng); 617 if (error) { 618 devres_free(ptr); 619 return error; 620 } 621 622 *ptr = rng; 623 devres_add(dev, ptr); 624 return 0; 625 } 626 EXPORT_SYMBOL_GPL(devm_hwrng_register); 627 628 void devm_hwrng_unregister(struct device *dev, struct hwrng *rng) 629 { 630 devres_release(dev, devm_hwrng_release, devm_hwrng_match, rng); 631 } 632 EXPORT_SYMBOL_GPL(devm_hwrng_unregister); 633 634 long hwrng_msleep(struct hwrng *rng, unsigned int msecs) 635 { 636 unsigned long timeout = msecs_to_jiffies(msecs) + 1; 637 638 return wait_for_completion_interruptible_timeout(&rng->dying, timeout); 639 } 640 EXPORT_SYMBOL_GPL(hwrng_msleep); 641 642 long hwrng_yield(struct hwrng *rng) 643 { 644 return wait_for_completion_interruptible_timeout(&rng->dying, 1); 645 } 646 EXPORT_SYMBOL_GPL(hwrng_yield); 647 648 static int __init hwrng_modinit(void) 649 { 650 int ret; 651 652 /* kmalloc makes this safe for virt_to_page() in virtio_rng.c */ 653 rng_buffer = kmalloc(rng_buffer_size(), GFP_KERNEL); 654 if (!rng_buffer) 655 return -ENOMEM; 656 657 rng_fillbuf = kmalloc(rng_buffer_size(), GFP_KERNEL); 658 if (!rng_fillbuf) { 659 kfree(rng_buffer); 660 return -ENOMEM; 661 } 662 663 ret = misc_register(&rng_miscdev); 664 if (ret) { 665 kfree(rng_fillbuf); 666 kfree(rng_buffer); 667 } 668 669 return ret; 670 } 671 672 static void __exit hwrng_modexit(void) 673 { 674 mutex_lock(&rng_mutex); 675 BUG_ON(current_rng); 676 kfree(rng_buffer); 677 kfree(rng_fillbuf); 678 mutex_unlock(&rng_mutex); 679 680 misc_deregister(&rng_miscdev); 681 } 682 683 fs_initcall(hwrng_modinit); /* depends on misc_register() */ 684 module_exit(hwrng_modexit); 685 686 MODULE_DESCRIPTION("H/W Random Number Generator (RNG) driver"); 687 MODULE_LICENSE("GPL"); 688