drivers/char/hw_random/core.c

   1 /*
   2         Added support for the AMD Geode LX RNG
   3         (c) Copyright 2004-2005 Advanced Micro Devices, Inc.
   4
   5         derived from
   6
   7         Hardware driver for the Intel/AMD/VIA Random Number Generators (RNG)
   8         (c) Copyright 2003 Red Hat Inc <jgarzik@redhat.com>
   9
  10         derived from
  11
  12         Hardware driver for the AMD 768 Random Number Generator (RNG)
  13         (c) Copyright 2001 Red Hat Inc <alan@redhat.com>
  14
  15         derived from
  16
  17         Hardware driver for Intel i810 Random Number Generator (RNG)
  18         Copyright 2000,2001 Jeff Garzik <jgarzik@pobox.com>
  19         Copyright 2000,2001 Philipp Rumpf <prumpf@mandrakesoft.com>
  20
  21         Added generic RNG API
  22         Copyright 2006 Michael Buesch <m@bues.ch>
  23         Copyright 2005 (c) MontaVista Software, Inc.
  24
  25         Please read Documentation/hw_random.txt for details on use.
  26
  27         ----------------------------------------------------------
  28         This software may be used and distributed according to the terms
  29         of the GNU General Public License, incorporated herein by reference.
  30
  31  */
  32
  33
  34 #include <linux/device.h>
  35 #include <linux/hw_random.h>
  36 #include <linux/module.h>
  37 #include <linux/kernel.h>
  38 #include <linux/fs.h>
  39 #include <linux/sched.h>
  40 #include <linux/miscdevice.h>
  41 #include <linux/kthread.h>
  42 #include <linux/delay.h>
  43 #include <linux/slab.h>
  44 #include <linux/random.h>
  45 #include <linux/err.h>
  46 #include <linux/uaccess.h>
  47
  48
  49 #define RNG_MODULE_NAME         "hw_random"
  50 #define PFX                     RNG_MODULE_NAME ": "
  51 #define RNG_MISCDEV_MINOR       183 /* official */
  52
  53
  54 static struct hwrng *current_rng;
  55 static struct task_struct *hwrng_fill;
  56 static LIST_HEAD(rng_list);
  57 /* Protects rng_list and current_rng */
  58 static DEFINE_MUTEX(rng_mutex);
  59 /* Protects rng read functions, data_avail, rng_buffer and rng_fillbuf */
  60 static DEFINE_MUTEX(reading_mutex);
  61 static int data_avail;
  62 static u8 *rng_buffer, *rng_fillbuf;
  63 static unsigned short current_quality;
  64 static unsigned short default_quality; /* = 0; default to "off" */
  65
  66 module_param(current_quality, ushort, 0644);
  67 MODULE_PARM_DESC(current_quality,
  68                  "current hwrng entropy estimation per mill");
  69 module_param(default_quality, ushort, 0644);
  70 MODULE_PARM_DESC(default_quality,
  71                  "default entropy content of hwrng per mill");
  72
  73 static void drop_current_rng(void);
  74 static int hwrng_init(struct hwrng *rng);
  75 static void start_khwrngd(void);
  76
  77 static inline int rng_get_data(struct hwrng *rng, u8 *buffer, size_t size,
  78                                int wait);
  79
  80 static size_t rng_buffer_size(void)
  81 {
  82         return SMP_CACHE_BYTES < 32 ? 32 : SMP_CACHE_BYTES;
  83 }
  84
  85 static void add_early_randomness(struct hwrng *rng)
  86 {
  87         int bytes_read;
  88         size_t size = min_t(size_t, 16, rng_buffer_size());
  89
  90         mutex_lock(&reading_mutex);
  91         bytes_read = rng_get_data(rng, rng_buffer, size, 1);
  92         mutex_unlock(&reading_mutex);
  93         if (bytes_read > 0)
  94                 add_device_randomness(rng_buffer, bytes_read);
  95         memset(rng_buffer, 0, size);
  96 }
  97
  98 static inline void cleanup_rng(struct kref *kref)
  99 {
 100         struct hwrng *rng = container_of(kref, struct hwrng, ref);
 101
 102         if (rng->cleanup)
 103                 rng->cleanup(rng);
 104
 105         complete(&rng->cleanup_done);
 106 }
 107
 108 static int set_current_rng(struct hwrng *rng)
 109 {
 110         int err;
 111
 112         BUG_ON(!mutex_is_locked(&rng_mutex));
 113
 114         err = hwrng_init(rng);
 115         if (err)
 116                 return err;
 117
 118         drop_current_rng();
 119         current_rng = rng;
 120
 121         return 0;
 122 }
 123
 124 static void drop_current_rng(void)
 125 {
 126         BUG_ON(!mutex_is_locked(&rng_mutex));
 127         if (!current_rng)
 128                 return;
 129
 130         /* decrease last reference for triggering the cleanup */
 131         kref_put(&current_rng->ref, cleanup_rng);
 132         current_rng = NULL;
 133 }
 134
 135 /* Returns ERR_PTR(), NULL or refcounted hwrng */
 136 static struct hwrng *get_current_rng(void)
 137 {
 138         struct hwrng *rng;
 139
 140         if (mutex_lock_interruptible(&rng_mutex))
 141                 return ERR_PTR(-ERESTARTSYS);
 142
 143         rng = current_rng;
 144         if (rng)
 145                 kref_get(&rng->ref);
 146
 147         mutex_unlock(&rng_mutex);
 148         return rng;
 149 }
 150
 151 static void put_rng(struct hwrng *rng)
 152 {
 153         /*
 154          * Hold rng_mutex here so we serialize in case they set_current_rng
 155          * on rng again immediately.
 156          */
 157         mutex_lock(&rng_mutex);
 158         if (rng)
 159                 kref_put(&rng->ref, cleanup_rng);
 160         mutex_unlock(&rng_mutex);
 161 }
 162
 163 static int hwrng_init(struct hwrng *rng)
 164 {
 165         if (kref_get_unless_zero(&rng->ref))
 166                 goto skip_init;
 167
 168         if (rng->init) {
 169                 int ret;
 170
 171                 ret =  rng->init(rng);
 172                 if (ret)
 173                         return ret;
 174         }
 175
 176         kref_init(&rng->ref);
 177         reinit_completion(&rng->cleanup_done);
 178
 179 skip_init:
 180         add_early_randomness(rng);
 181
 182         current_quality = rng->quality ? : default_quality;
 183         if (current_quality > 1024)
 184                 current_quality = 1024;
 185
 186         if (current_quality == 0 && hwrng_fill)
 187                 kthread_stop(hwrng_fill);
 188         if (current_quality > 0 && !hwrng_fill)
 189                 start_khwrngd();
 190
 191         return 0;
 192 }
 193
 194 static int rng_dev_open(struct inode *inode, struct file *filp)
 195 {
 196         /* enforce read-only access to this chrdev */
 197         if ((filp->f_mode & FMODE_READ) == 0)
 198                 return -EINVAL;
 199         if (filp->f_mode & FMODE_WRITE)
 200                 return -EINVAL;
 201         return 0;
 202 }
 203
 204 static inline int rng_get_data(struct hwrng *rng, u8 *buffer, size_t size,
 205                         int wait) {
 206         int present;
 207
 208         BUG_ON(!mutex_is_locked(&reading_mutex));
 209         if (rng->read)
 210                 return rng->read(rng, (void *)buffer, size, wait);
 211
 212         if (rng->data_present)
 213                 present = rng->data_present(rng, wait);
 214         else
 215                 present = 1;
 216
 217         if (present)
 218                 return rng->data_read(rng, (u32 *)buffer);
 219
 220         return 0;
 221 }
 222
 223 static ssize_t rng_dev_read(struct file *filp, char __user *buf,
 224                             size_t size, loff_t *offp)
 225 {
 226         ssize_t ret = 0;
 227         int err = 0;
 228         int bytes_read, len;
 229         struct hwrng *rng;
 230
 231         while (size) {
 232                 rng = get_current_rng();
 233                 if (IS_ERR(rng)) {
 234                         err = PTR_ERR(rng);
 235                         goto out;
 236                 }
 237                 if (!rng) {
 238                         err = -ENODEV;
 239                         goto out;
 240                 }
 241
 242                 if (mutex_lock_interruptible(&reading_mutex)) {
 243                         err = -ERESTARTSYS;
 244                         goto out_put;
 245                 }
 246                 if (!data_avail) {
 247                         bytes_read = rng_get_data(rng, rng_buffer,
 248                                 rng_buffer_size(),
 249                                 !(filp->f_flags & O_NONBLOCK));
 250                         if (bytes_read < 0) {
 251                                 err = bytes_read;
 252                                 goto out_unlock_reading;
 253                         }
 254                         data_avail = bytes_read;
 255                 }
 256
 257                 if (!data_avail) {
 258                         if (filp->f_flags & O_NONBLOCK) {
 259                                 err = -EAGAIN;
 260                                 goto out_unlock_reading;
 261                         }
 262                 } else {
 263                         len = data_avail;
 264                         if (len > size)
 265                                 len = size;
 266
 267                         data_avail -= len;
 268
 269                         if (copy_to_user(buf + ret, rng_buffer + data_avail,
 270                                                                 len)) {
 271                                 err = -EFAULT;
 272                                 goto out_unlock_reading;
 273                         }
 274
 275                         size -= len;
 276                         ret += len;
 277                 }
 278
 279                 mutex_unlock(&reading_mutex);
 280                 put_rng(rng);
 281
 282                 if (need_resched())
 283                         schedule_timeout_interruptible(1);
 284
 285                 if (signal_pending(current)) {
 286                         err = -ERESTARTSYS;
 287                         goto out;
 288                 }
 289         }
 290 out:
 291         memset(rng_buffer, 0, rng_buffer_size());
 292         return ret ? : err;
 293
 294 out_unlock_reading:
 295         mutex_unlock(&reading_mutex);
 296 out_put:
 297         put_rng(rng);
 298         goto out;
 299 }
 300
 301
 302 static const struct file_operations rng_chrdev_ops = {
 303         .owner          = THIS_MODULE,
 304         .open           = rng_dev_open,
 305         .read           = rng_dev_read,
 306         .llseek         = noop_llseek,
 307 };
 308
 309 static const struct attribute_group *rng_dev_groups[];
 310
 311 static struct miscdevice rng_miscdev = {
 312         .minor          = RNG_MISCDEV_MINOR,
 313         .name           = RNG_MODULE_NAME,
 314         .nodename       = "hwrng",
 315         .fops           = &rng_chrdev_ops,
 316         .groups         = rng_dev_groups,
 317 };
 318
 319
 320 static ssize_t hwrng_attr_current_store(struct device *dev,
 321                                         struct device_attribute *attr,
 322                                         const char *buf, size_t len)
 323 {
 324         int err;
 325         struct hwrng *rng;
 326
 327         err = mutex_lock_interruptible(&rng_mutex);
 328         if (err)
 329                 return -ERESTARTSYS;
 330         err = -ENODEV;
 331         list_for_each_entry(rng, &rng_list, list) {
 332                 if (sysfs_streq(rng->name, buf)) {
 333                         err = 0;
 334                         if (rng != current_rng)
 335                                 err = set_current_rng(rng);
 336                         break;
 337                 }
 338         }
 339         mutex_unlock(&rng_mutex);
 340
 341         return err ? : len;
 342 }
 343
 344 static ssize_t hwrng_attr_current_show(struct device *dev,
 345                                        struct device_attribute *attr,
 346                                        char *buf)
 347 {
 348         ssize_t ret;
 349         struct hwrng *rng;
 350
 351         rng = get_current_rng();
 352         if (IS_ERR(rng))
 353                 return PTR_ERR(rng);
 354
 355         ret = snprintf(buf, PAGE_SIZE, "%s\n", rng ? rng->name : "none");
 356         put_rng(rng);
 357
 358         return ret;
 359 }
 360
 361 static ssize_t hwrng_attr_available_show(struct device *dev,
 362                                          struct device_attribute *attr,
 363                                          char *buf)
 364 {
 365         int err;
 366         struct hwrng *rng;
 367
 368         err = mutex_lock_interruptible(&rng_mutex);
 369         if (err)
 370                 return -ERESTARTSYS;
 371         buf[0] = '\0';
 372         list_for_each_entry(rng, &rng_list, list) {
 373                 strlcat(buf, rng->name, PAGE_SIZE);
 374                 strlcat(buf, " ", PAGE_SIZE);
 375         }
 376         strlcat(buf, "\n", PAGE_SIZE);
 377         mutex_unlock(&rng_mutex);
 378
 379         return strlen(buf);
 380 }
 381
 382 static DEVICE_ATTR(rng_current, S_IRUGO | S_IWUSR,
 383                    hwrng_attr_current_show,
 384                    hwrng_attr_current_store);
 385 static DEVICE_ATTR(rng_available, S_IRUGO,
 386                    hwrng_attr_available_show,
 387                    NULL);
 388
 389 static struct attribute *rng_dev_attrs[] = {
 390         &dev_attr_rng_current.attr,
 391         &dev_attr_rng_available.attr,
 392         NULL
 393 };
 394
 395 ATTRIBUTE_GROUPS(rng_dev);
 396
 397 static void __exit unregister_miscdev(void)
 398 {
 399         misc_deregister(&rng_miscdev);
 400 }
 401
 402 static int __init register_miscdev(void)
 403 {
 404         return misc_register(&rng_miscdev);
 405 }
 406
 407 static int hwrng_fillfn(void *unused)
 408 {
 409         long rc;
 410
 411         while (!kthread_should_stop()) {
 412                 struct hwrng *rng;
 413
 414                 rng = get_current_rng();
 415                 if (IS_ERR(rng) || !rng)
 416                         break;
 417                 mutex_lock(&reading_mutex);
 418                 rc = rng_get_data(rng, rng_fillbuf,
 419                                   rng_buffer_size(), 1);
 420                 mutex_unlock(&reading_mutex);
 421                 put_rng(rng);
 422                 if (rc <= 0) {
 423                         pr_warn("hwrng: no data available\n");
 424                         msleep_interruptible(10000);
 425                         continue;
 426                 }
 427                 /* Outside lock, sure, but y'know: randomness. */
 428                 add_hwgenerator_randomness((void *)rng_fillbuf, rc,
 429                                            rc * current_quality * 8 >> 10);
 430                 memset(rng_fillbuf, 0, rng_buffer_size());
 431         }
 432         hwrng_fill = NULL;
 433         return 0;
 434 }
 435
 436 static void start_khwrngd(void)
 437 {
 438         hwrng_fill = kthread_run(hwrng_fillfn, NULL, "hwrng");
 439         if (IS_ERR(hwrng_fill)) {
 440                 pr_err("hwrng_fill thread creation failed");
 441                 hwrng_fill = NULL;
 442         }
 443 }
 444
 445 int hwrng_register(struct hwrng *rng)
 446 {
 447         int err = -EINVAL;
 448         struct hwrng *old_rng, *tmp;
 449
 450         if (rng->name == NULL ||
 451             (rng->data_read == NULL && rng->read == NULL))
 452                 goto out;
 453
 454         mutex_lock(&rng_mutex);
 455         /* Must not register two RNGs with the same name. */
 456         err = -EEXIST;
 457         list_for_each_entry(tmp, &rng_list, list) {
 458                 if (strcmp(tmp->name, rng->name) == 0)
 459                         goto out_unlock;
 460         }
 461
 462         init_completion(&rng->cleanup_done);
 463         complete(&rng->cleanup_done);
 464
 465         old_rng = current_rng;
 466         err = 0;
 467         if (!old_rng) {
 468                 err = set_current_rng(rng);
 469                 if (err)
 470                         goto out_unlock;
 471         }
 472         list_add_tail(&rng->list, &rng_list);
 473
 474         if (old_rng && !rng->init) {
 475                 /*
 476                  * Use a new device's input to add some randomness to
 477                  * the system.  If this rng device isn't going to be
 478                  * used right away, its init function hasn't been
 479                  * called yet; so only use the randomness from devices
 480                  * that don't need an init callback.
 481                  */
 482                 add_early_randomness(rng);
 483         }
 484
 485 out_unlock:
 486         mutex_unlock(&rng_mutex);
 487 out:
 488         return err;
 489 }
 490 EXPORT_SYMBOL_GPL(hwrng_register);
 491
 492 void hwrng_unregister(struct hwrng *rng)
 493 {
 494         mutex_lock(&rng_mutex);
 495
 496         list_del(&rng->list);
 497         if (current_rng == rng) {
 498                 drop_current_rng();
 499                 if (!list_empty(&rng_list)) {
 500                         struct hwrng *tail;
 501
 502                         tail = list_entry(rng_list.prev, struct hwrng, list);
 503
 504                         set_current_rng(tail);
 505                 }
 506         }
 507
 508         if (list_empty(&rng_list)) {
 509                 mutex_unlock(&rng_mutex);
 510                 if (hwrng_fill)
 511                         kthread_stop(hwrng_fill);
 512         } else
 513                 mutex_unlock(&rng_mutex);
 514
 515         wait_for_completion(&rng->cleanup_done);
 516 }
 517 EXPORT_SYMBOL_GPL(hwrng_unregister);
 518
 519 static void devm_hwrng_release(struct device *dev, void *res)
 520 {
 521         hwrng_unregister(*(struct hwrng **)res);
 522 }
 523
 524 static int devm_hwrng_match(struct device *dev, void *res, void *data)
 525 {
 526         struct hwrng **r = res;
 527
 528         if (WARN_ON(!r || !*r))
 529                 return 0;
 530
 531         return *r == data;
 532 }
 533
 534 int devm_hwrng_register(struct device *dev, struct hwrng *rng)
 535 {
 536         struct hwrng **ptr;
 537         int error;
 538
 539         ptr = devres_alloc(devm_hwrng_release, sizeof(*ptr), GFP_KERNEL);
 540         if (!ptr)
 541                 return -ENOMEM;
 542
 543         error = hwrng_register(rng);
 544         if (error) {
 545                 devres_free(ptr);
 546                 return error;
 547         }
 548
 549         *ptr = rng;
 550         devres_add(dev, ptr);
 551         return 0;
 552 }
 553 EXPORT_SYMBOL_GPL(devm_hwrng_register);
 554
 555 void devm_hwrng_unregister(struct device *dev, struct hwrng *rng)
 556 {
 557         devres_release(dev, devm_hwrng_release, devm_hwrng_match, rng);
 558 }
 559 EXPORT_SYMBOL_GPL(devm_hwrng_unregister);
 560
 561 static int __init hwrng_modinit(void)
 562 {
 563         int ret = -ENOMEM;
 564
 565         /* kmalloc makes this safe for virt_to_page() in virtio_rng.c */
 566         rng_buffer = kmalloc(rng_buffer_size(), GFP_KERNEL);
 567         if (!rng_buffer)
 568                 return -ENOMEM;
 569
 570         rng_fillbuf = kmalloc(rng_buffer_size(), GFP_KERNEL);
 571         if (!rng_fillbuf) {
 572                 kfree(rng_buffer);
 573                 return -ENOMEM;
 574         }
 575
 576         ret = register_miscdev();
 577         if (ret) {
 578                 kfree(rng_fillbuf);
 579                 kfree(rng_buffer);
 580         }
 581
 582         return ret;
 583 }
 584
 585 static void __exit hwrng_modexit(void)
 586 {
 587         mutex_lock(&rng_mutex);
 588         BUG_ON(current_rng);
 589         kfree(rng_buffer);
 590         kfree(rng_fillbuf);
 591         mutex_unlock(&rng_mutex);
 592
 593         unregister_miscdev();
 594 }
 595
 596 module_init(hwrng_modinit);
 597 module_exit(hwrng_modexit);
 598
 599 MODULE_DESCRIPTION("H/W Random Number Generator (RNG) driver");
 600 MODULE_LICENSE("GPL");