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