drivers/char/hw_random/core.c

   1 /*
   2  * hw_random/core.c: HWRNG core API
   3  *
   4  * Copyright 2006 Michael Buesch <[email protected]>
   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                 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");