drivers/char/hw_random/core.c

   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(&current_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(&current_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");