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         current_quality &= 1023;
 183
 184         if (current_quality == 0 && hwrng_fill)
 185                 kthread_stop(hwrng_fill);
 186         if (current_quality > 0 && !hwrng_fill)
 187                 start_khwrngd();
 188
 189         return 0;
 190 }
 191
 192 static int rng_dev_open(struct inode *inode, struct file *filp)
 193 {
 194         /* enforce read-only access to this chrdev */
 195         if ((filp->f_mode & FMODE_READ) == 0)
 196                 return -EINVAL;
 197         if (filp->f_mode & FMODE_WRITE)
 198                 return -EINVAL;
 199         return 0;
 200 }
 201
 202 static inline int rng_get_data(struct hwrng *rng, u8 *buffer, size_t size,
 203                         int wait) {
 204         int present;
 205
 206         BUG_ON(!mutex_is_locked(&reading_mutex));
 207         if (rng->read)
 208                 return rng->read(rng, (void *)buffer, size, wait);
 209
 210         if (rng->data_present)
 211                 present = rng->data_present(rng, wait);
 212         else
 213                 present = 1;
 214
 215         if (present)
 216                 return rng->data_read(rng, (u32 *)buffer);
 217
 218         return 0;
 219 }
 220
 221 static ssize_t rng_dev_read(struct file *filp, char __user *buf,
 222                             size_t size, loff_t *offp)
 223 {
 224         ssize_t ret = 0;
 225         int err = 0;
 226         int bytes_read, len;
 227         struct hwrng *rng;
 228
 229         while (size) {
 230                 rng = get_current_rng();
 231                 if (IS_ERR(rng)) {
 232                         err = PTR_ERR(rng);
 233                         goto out;
 234                 }
 235                 if (!rng) {
 236                         err = -ENODEV;
 237                         goto out;
 238                 }
 239
 240                 mutex_lock(&reading_mutex);
 241                 if (!data_avail) {
 242                         bytes_read = rng_get_data(rng, rng_buffer,
 243                                 rng_buffer_size(),
 244                                 !(filp->f_flags & O_NONBLOCK));
 245                         if (bytes_read < 0) {
 246                                 err = bytes_read;
 247                                 goto out_unlock_reading;
 248                         }
 249                         data_avail = bytes_read;
 250                 }
 251
 252                 if (!data_avail) {
 253                         if (filp->f_flags & O_NONBLOCK) {
 254                                 err = -EAGAIN;
 255                                 goto out_unlock_reading;
 256                         }
 257                 } else {
 258                         len = data_avail;
 259                         if (len > size)
 260                                 len = size;
 261
 262                         data_avail -= len;
 263
 264                         if (copy_to_user(buf + ret, rng_buffer + data_avail,
 265                                                                 len)) {
 266                                 err = -EFAULT;
 267                                 goto out_unlock_reading;
 268                         }
 269
 270                         size -= len;
 271                         ret += len;
 272                 }
 273
 274                 mutex_unlock(&reading_mutex);
 275                 put_rng(rng);
 276
 277                 if (need_resched())
 278                         schedule_timeout_interruptible(1);
 279
 280                 if (signal_pending(current)) {
 281                         err = -ERESTARTSYS;
 282                         goto out;
 283                 }
 284         }
 285 out:
 286         return ret ? : err;
 287
 288 out_unlock_reading:
 289         mutex_unlock(&reading_mutex);
 290         put_rng(rng);
 291         goto out;
 292 }
 293
 294
 295 static const struct file_operations rng_chrdev_ops = {
 296         .owner          = THIS_MODULE,
 297         .open           = rng_dev_open,
 298         .read           = rng_dev_read,
 299         .llseek         = noop_llseek,
 300 };
 301
 302 static struct miscdevice rng_miscdev = {
 303         .minor          = RNG_MISCDEV_MINOR,
 304         .name           = RNG_MODULE_NAME,
 305         .nodename       = "hwrng",
 306         .fops           = &rng_chrdev_ops,
 307 };
 308
 309
 310 static ssize_t hwrng_attr_current_store(struct device *dev,
 311                                         struct device_attribute *attr,
 312                                         const char *buf, size_t len)
 313 {
 314         int err;
 315         struct hwrng *rng;
 316
 317         err = mutex_lock_interruptible(&rng_mutex);
 318         if (err)
 319                 return -ERESTARTSYS;
 320         err = -ENODEV;
 321         list_for_each_entry(rng, &rng_list, list) {
 322                 if (strcmp(rng->name, buf) == 0) {
 323                         err = 0;
 324                         if (rng != current_rng)
 325                                 err = set_current_rng(rng);
 326                         break;
 327                 }
 328         }
 329         mutex_unlock(&rng_mutex);
 330
 331         return err ? : len;
 332 }
 333
 334 static ssize_t hwrng_attr_current_show(struct device *dev,
 335                                        struct device_attribute *attr,
 336                                        char *buf)
 337 {
 338         ssize_t ret;
 339         struct hwrng *rng;
 340
 341         rng = get_current_rng();
 342         if (IS_ERR(rng))
 343                 return PTR_ERR(rng);
 344
 345         ret = snprintf(buf, PAGE_SIZE, "%s\n", rng ? rng->name : "none");
 346         put_rng(rng);
 347
 348         return ret;
 349 }
 350
 351 static ssize_t hwrng_attr_available_show(struct device *dev,
 352                                          struct device_attribute *attr,
 353                                          char *buf)
 354 {
 355         int err;
 356         struct hwrng *rng;
 357
 358         err = mutex_lock_interruptible(&rng_mutex);
 359         if (err)
 360                 return -ERESTARTSYS;
 361         buf[0] = '\0';
 362         list_for_each_entry(rng, &rng_list, list) {
 363                 strlcat(buf, rng->name, PAGE_SIZE);
 364                 strlcat(buf, " ", PAGE_SIZE);
 365         }
 366         strlcat(buf, "\n", PAGE_SIZE);
 367         mutex_unlock(&rng_mutex);
 368
 369         return strlen(buf);
 370 }
 371
 372 static DEVICE_ATTR(rng_current, S_IRUGO | S_IWUSR,
 373                    hwrng_attr_current_show,
 374                    hwrng_attr_current_store);
 375 static DEVICE_ATTR(rng_available, S_IRUGO,
 376                    hwrng_attr_available_show,
 377                    NULL);
 378
 379
 380 static void __exit unregister_miscdev(void)
 381 {
 382         device_remove_file(rng_miscdev.this_device, &dev_attr_rng_available);
 383         device_remove_file(rng_miscdev.this_device, &dev_attr_rng_current);
 384         misc_deregister(&rng_miscdev);
 385 }
 386
 387 static int __init register_miscdev(void)
 388 {
 389         int err;
 390
 391         err = misc_register(&rng_miscdev);
 392         if (err)
 393                 goto out;
 394         err = device_create_file(rng_miscdev.this_device,
 395                                  &dev_attr_rng_current);
 396         if (err)
 397                 goto err_misc_dereg;
 398         err = device_create_file(rng_miscdev.this_device,
 399                                  &dev_attr_rng_available);
 400         if (err)
 401                 goto err_remove_current;
 402 out:
 403         return err;
 404
 405 err_remove_current:
 406         device_remove_file(rng_miscdev.this_device, &dev_attr_rng_current);
 407 err_misc_dereg:
 408         misc_deregister(&rng_miscdev);
 409         goto out;
 410 }
 411
 412 static int hwrng_fillfn(void *unused)
 413 {
 414         long rc;
 415
 416         while (!kthread_should_stop()) {
 417                 struct hwrng *rng;
 418
 419                 rng = get_current_rng();
 420                 if (IS_ERR(rng) || !rng)
 421                         break;
 422                 mutex_lock(&reading_mutex);
 423                 rc = rng_get_data(rng, rng_fillbuf,
 424                                   rng_buffer_size(), 1);
 425                 mutex_unlock(&reading_mutex);
 426                 put_rng(rng);
 427                 if (rc <= 0) {
 428                         pr_warn("hwrng: no data available\n");
 429                         msleep_interruptible(10000);
 430                         continue;
 431                 }
 432                 /* Outside lock, sure, but y'know: randomness. */
 433                 add_hwgenerator_randomness((void *)rng_fillbuf, rc,
 434                                            rc * current_quality * 8 >> 10);
 435         }
 436         hwrng_fill = NULL;
 437         return 0;
 438 }
 439
 440 static void start_khwrngd(void)
 441 {
 442         hwrng_fill = kthread_run(hwrng_fillfn, NULL, "hwrng");
 443         if (hwrng_fill == ERR_PTR(-ENOMEM)) {
 444                 pr_err("hwrng_fill thread creation failed");
 445                 hwrng_fill = NULL;
 446         }
 447 }
 448
 449 int hwrng_register(struct hwrng *rng)
 450 {
 451         int err = -EINVAL;
 452         struct hwrng *old_rng, *tmp;
 453
 454         if (rng->name == NULL ||
 455             (rng->data_read == NULL && rng->read == NULL))
 456                 goto out;
 457
 458         mutex_lock(&rng_mutex);
 459
 460         /* kmalloc makes this safe for virt_to_page() in virtio_rng.c */
 461         err = -ENOMEM;
 462         if (!rng_buffer) {
 463                 rng_buffer = kmalloc(rng_buffer_size(), GFP_KERNEL);
 464                 if (!rng_buffer)
 465                         goto out_unlock;
 466         }
 467         if (!rng_fillbuf) {
 468                 rng_fillbuf = kmalloc(rng_buffer_size(), GFP_KERNEL);
 469                 if (!rng_fillbuf) {
 470                         kfree(rng_buffer);
 471                         goto out_unlock;
 472                 }
 473         }
 474
 475         /* Must not register two RNGs with the same name. */
 476         err = -EEXIST;
 477         list_for_each_entry(tmp, &rng_list, list) {
 478                 if (strcmp(tmp->name, rng->name) == 0)
 479                         goto out_unlock;
 480         }
 481
 482         init_completion(&rng->cleanup_done);
 483         complete(&rng->cleanup_done);
 484
 485         old_rng = current_rng;
 486         err = 0;
 487         if (!old_rng) {
 488                 err = set_current_rng(rng);
 489                 if (err)
 490                         goto out_unlock;
 491         }
 492         list_add_tail(&rng->list, &rng_list);
 493
 494         if (old_rng && !rng->init) {
 495                 /*
 496                  * Use a new device's input to add some randomness to
 497                  * the system.  If this rng device isn't going to be
 498                  * used right away, its init function hasn't been
 499                  * called yet; so only use the randomness from devices
 500                  * that don't need an init callback.
 501                  */
 502                 add_early_randomness(rng);
 503         }
 504
 505 out_unlock:
 506         mutex_unlock(&rng_mutex);
 507 out:
 508         return err;
 509 }
 510 EXPORT_SYMBOL_GPL(hwrng_register);
 511
 512 void hwrng_unregister(struct hwrng *rng)
 513 {
 514         mutex_lock(&rng_mutex);
 515
 516         list_del(&rng->list);
 517         if (current_rng == rng) {
 518                 drop_current_rng();
 519                 if (!list_empty(&rng_list)) {
 520                         struct hwrng *tail;
 521
 522                         tail = list_entry(rng_list.prev, struct hwrng, list);
 523
 524                         set_current_rng(tail);
 525                 }
 526         }
 527
 528         if (list_empty(&rng_list)) {
 529                 mutex_unlock(&rng_mutex);
 530                 if (hwrng_fill)
 531                         kthread_stop(hwrng_fill);
 532         } else
 533                 mutex_unlock(&rng_mutex);
 534
 535         wait_for_completion(&rng->cleanup_done);
 536 }
 537 EXPORT_SYMBOL_GPL(hwrng_unregister);
 538
 539 static int __init hwrng_modinit(void)
 540 {
 541         return register_miscdev();
 542 }
 543
 544 static void __exit hwrng_modexit(void)
 545 {
 546         mutex_lock(&rng_mutex);
 547         BUG_ON(current_rng);
 548         kfree(rng_buffer);
 549         kfree(rng_fillbuf);
 550         mutex_unlock(&rng_mutex);
 551
 552         unregister_miscdev();
 553 }
 554
 555 module_init(hwrng_modinit);
 556 module_exit(hwrng_modexit);
 557
 558 MODULE_DESCRIPTION("H/W Random Number Generator (RNG) driver");
 559 MODULE_LICENSE("GPL");