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                 mutex_lock(&reading_mutex);
 242                 if (!data_avail) {
 243                         bytes_read = rng_get_data(rng, rng_buffer,
 244                                 rng_buffer_size(),
 245                                 !(filp->f_flags & O_NONBLOCK));
 246                         if (bytes_read < 0) {
 247                                 err = bytes_read;
 248                                 goto out_unlock_reading;
 249                         }
 250                         data_avail = bytes_read;
 251                 }
 252
 253                 if (!data_avail) {
 254                         if (filp->f_flags & O_NONBLOCK) {
 255                                 err = -EAGAIN;
 256                                 goto out_unlock_reading;
 257                         }
 258                 } else {
 259                         len = data_avail;
 260                         if (len > size)
 261                                 len = size;
 262
 263                         data_avail -= len;
 264
 265                         if (copy_to_user(buf + ret, rng_buffer + data_avail,
 266                                                                 len)) {
 267                                 err = -EFAULT;
 268                                 goto out_unlock_reading;
 269                         }
 270
 271                         size -= len;
 272                         ret += len;
 273                 }
 274
 275                 mutex_unlock(&reading_mutex);
 276                 put_rng(rng);
 277
 278                 if (need_resched())
 279                         schedule_timeout_interruptible(1);
 280
 281                 if (signal_pending(current)) {
 282                         err = -ERESTARTSYS;
 283                         goto out;
 284                 }
 285         }
 286 out:
 287         return ret ? : err;
 288
 289 out_unlock_reading:
 290         mutex_unlock(&reading_mutex);
 291         put_rng(rng);
 292         goto out;
 293 }
 294
 295
 296 static const struct file_operations rng_chrdev_ops = {
 297         .owner          = THIS_MODULE,
 298         .open           = rng_dev_open,
 299         .read           = rng_dev_read,
 300         .llseek         = noop_llseek,
 301 };
 302
 303 static const struct attribute_group *rng_dev_groups[];
 304
 305 static struct miscdevice rng_miscdev = {
 306         .minor          = RNG_MISCDEV_MINOR,
 307         .name           = RNG_MODULE_NAME,
 308         .nodename       = "hwrng",
 309         .fops           = &rng_chrdev_ops,
 310         .groups         = rng_dev_groups,
 311 };
 312
 313
 314 static ssize_t hwrng_attr_current_store(struct device *dev,
 315                                         struct device_attribute *attr,
 316                                         const char *buf, size_t len)
 317 {
 318         int err;
 319         struct hwrng *rng;
 320
 321         err = mutex_lock_interruptible(&rng_mutex);
 322         if (err)
 323                 return -ERESTARTSYS;
 324         err = -ENODEV;
 325         list_for_each_entry(rng, &rng_list, list) {
 326                 if (strcmp(rng->name, buf) == 0) {
 327                         err = 0;
 328                         if (rng != current_rng)
 329                                 err = set_current_rng(rng);
 330                         break;
 331                 }
 332         }
 333         mutex_unlock(&rng_mutex);
 334
 335         return err ? : len;
 336 }
 337
 338 static ssize_t hwrng_attr_current_show(struct device *dev,
 339                                        struct device_attribute *attr,
 340                                        char *buf)
 341 {
 342         ssize_t ret;
 343         struct hwrng *rng;
 344
 345         rng = get_current_rng();
 346         if (IS_ERR(rng))
 347                 return PTR_ERR(rng);
 348
 349         ret = snprintf(buf, PAGE_SIZE, "%s\n", rng ? rng->name : "none");
 350         put_rng(rng);
 351
 352         return ret;
 353 }
 354
 355 static ssize_t hwrng_attr_available_show(struct device *dev,
 356                                          struct device_attribute *attr,
 357                                          char *buf)
 358 {
 359         int err;
 360         struct hwrng *rng;
 361
 362         err = mutex_lock_interruptible(&rng_mutex);
 363         if (err)
 364                 return -ERESTARTSYS;
 365         buf[0] = '\0';
 366         list_for_each_entry(rng, &rng_list, list) {
 367                 strlcat(buf, rng->name, PAGE_SIZE);
 368                 strlcat(buf, " ", PAGE_SIZE);
 369         }
 370         strlcat(buf, "\n", PAGE_SIZE);
 371         mutex_unlock(&rng_mutex);
 372
 373         return strlen(buf);
 374 }
 375
 376 static DEVICE_ATTR(rng_current, S_IRUGO | S_IWUSR,
 377                    hwrng_attr_current_show,
 378                    hwrng_attr_current_store);
 379 static DEVICE_ATTR(rng_available, S_IRUGO,
 380                    hwrng_attr_available_show,
 381                    NULL);
 382
 383 static struct attribute *rng_dev_attrs[] = {
 384         &dev_attr_rng_current.attr,
 385         &dev_attr_rng_available.attr,
 386         NULL
 387 };
 388
 389 ATTRIBUTE_GROUPS(rng_dev);
 390
 391 static void __exit unregister_miscdev(void)
 392 {
 393         misc_deregister(&rng_miscdev);
 394 }
 395
 396 static int __init register_miscdev(void)
 397 {
 398         return misc_register(&rng_miscdev);
 399 }
 400
 401 static int hwrng_fillfn(void *unused)
 402 {
 403         long rc;
 404
 405         while (!kthread_should_stop()) {
 406                 struct hwrng *rng;
 407
 408                 rng = get_current_rng();
 409                 if (IS_ERR(rng) || !rng)
 410                         break;
 411                 mutex_lock(&reading_mutex);
 412                 rc = rng_get_data(rng, rng_fillbuf,
 413                                   rng_buffer_size(), 1);
 414                 mutex_unlock(&reading_mutex);
 415                 put_rng(rng);
 416                 if (rc <= 0) {
 417                         pr_warn("hwrng: no data available\n");
 418                         msleep_interruptible(10000);
 419                         continue;
 420                 }
 421                 /* Outside lock, sure, but y'know: randomness. */
 422                 add_hwgenerator_randomness((void *)rng_fillbuf, rc,
 423                                            rc * current_quality * 8 >> 10);
 424         }
 425         hwrng_fill = NULL;
 426         return 0;
 427 }
 428
 429 static void start_khwrngd(void)
 430 {
 431         hwrng_fill = kthread_run(hwrng_fillfn, NULL, "hwrng");
 432         if (IS_ERR(hwrng_fill)) {
 433                 pr_err("hwrng_fill thread creation failed");
 434                 hwrng_fill = NULL;
 435         }
 436 }
 437
 438 int hwrng_register(struct hwrng *rng)
 439 {
 440         int err = -EINVAL;
 441         struct hwrng *old_rng, *tmp;
 442
 443         if (rng->name == NULL ||
 444             (rng->data_read == NULL && rng->read == NULL))
 445                 goto out;
 446
 447         mutex_lock(&rng_mutex);
 448
 449         /* kmalloc makes this safe for virt_to_page() in virtio_rng.c */
 450         err = -ENOMEM;
 451         if (!rng_buffer) {
 452                 rng_buffer = kmalloc(rng_buffer_size(), GFP_KERNEL);
 453                 if (!rng_buffer)
 454                         goto out_unlock;
 455         }
 456         if (!rng_fillbuf) {
 457                 rng_fillbuf = kmalloc(rng_buffer_size(), GFP_KERNEL);
 458                 if (!rng_fillbuf) {
 459                         kfree(rng_buffer);
 460                         goto out_unlock;
 461                 }
 462         }
 463
 464         /* Must not register two RNGs with the same name. */
 465         err = -EEXIST;
 466         list_for_each_entry(tmp, &rng_list, list) {
 467                 if (strcmp(tmp->name, rng->name) == 0)
 468                         goto out_unlock;
 469         }
 470
 471         init_completion(&rng->cleanup_done);
 472         complete(&rng->cleanup_done);
 473
 474         old_rng = current_rng;
 475         err = 0;
 476         if (!old_rng) {
 477                 err = set_current_rng(rng);
 478                 if (err)
 479                         goto out_unlock;
 480         }
 481         list_add_tail(&rng->list, &rng_list);
 482
 483         if (old_rng && !rng->init) {
 484                 /*
 485                  * Use a new device's input to add some randomness to
 486                  * the system.  If this rng device isn't going to be
 487                  * used right away, its init function hasn't been
 488                  * called yet; so only use the randomness from devices
 489                  * that don't need an init callback.
 490                  */
 491                 add_early_randomness(rng);
 492         }
 493
 494 out_unlock:
 495         mutex_unlock(&rng_mutex);
 496 out:
 497         return err;
 498 }
 499 EXPORT_SYMBOL_GPL(hwrng_register);
 500
 501 void hwrng_unregister(struct hwrng *rng)
 502 {
 503         mutex_lock(&rng_mutex);
 504
 505         list_del(&rng->list);
 506         if (current_rng == rng) {
 507                 drop_current_rng();
 508                 if (!list_empty(&rng_list)) {
 509                         struct hwrng *tail;
 510
 511                         tail = list_entry(rng_list.prev, struct hwrng, list);
 512
 513                         set_current_rng(tail);
 514                 }
 515         }
 516
 517         if (list_empty(&rng_list)) {
 518                 mutex_unlock(&rng_mutex);
 519                 if (hwrng_fill)
 520                         kthread_stop(hwrng_fill);
 521         } else
 522                 mutex_unlock(&rng_mutex);
 523
 524         wait_for_completion(&rng->cleanup_done);
 525 }
 526 EXPORT_SYMBOL_GPL(hwrng_unregister);
 527
 528 static void devm_hwrng_release(struct device *dev, void *res)
 529 {
 530         hwrng_unregister(*(struct hwrng **)res);
 531 }
 532
 533 static int devm_hwrng_match(struct device *dev, void *res, void *data)
 534 {
 535         struct hwrng **r = res;
 536
 537         if (WARN_ON(!r || !*r))
 538                 return 0;
 539
 540         return *r == data;
 541 }
 542
 543 int devm_hwrng_register(struct device *dev, struct hwrng *rng)
 544 {
 545         struct hwrng **ptr;
 546         int error;
 547
 548         ptr = devres_alloc(devm_hwrng_release, sizeof(*ptr), GFP_KERNEL);
 549         if (!ptr)
 550                 return -ENOMEM;
 551
 552         error = hwrng_register(rng);
 553         if (error) {
 554                 devres_free(ptr);
 555                 return error;
 556         }
 557
 558         *ptr = rng;
 559         devres_add(dev, ptr);
 560         return 0;
 561 }
 562 EXPORT_SYMBOL_GPL(devm_hwrng_register);
 563
 564 void devm_hwrng_unregister(struct device *dev, struct hwrng *rng)
 565 {
 566         devres_release(dev, devm_hwrng_release, devm_hwrng_match, rng);
 567 }
 568 EXPORT_SYMBOL_GPL(devm_hwrng_unregister);
 569
 570 static int __init hwrng_modinit(void)
 571 {
 572         return register_miscdev();
 573 }
 574
 575 static void __exit hwrng_modexit(void)
 576 {
 577         mutex_lock(&rng_mutex);
 578         BUG_ON(current_rng);
 579         kfree(rng_buffer);
 580         kfree(rng_fillbuf);
 581         mutex_unlock(&rng_mutex);
 582
 583         unregister_miscdev();
 584 }
 585
 586 module_init(hwrng_modinit);
 587 module_exit(hwrng_modexit);
 588
 589 MODULE_DESCRIPTION("H/W Random Number Generator (RNG) driver");
 590 MODULE_LICENSE("GPL");