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 start_khwrngd(void);
  74
  75 static inline int rng_get_data(struct hwrng *rng, u8 *buffer, size_t size,
  76                                int wait);
  77
  78 static size_t rng_buffer_size(void)
  79 {
  80         return SMP_CACHE_BYTES < 32 ? 32 : SMP_CACHE_BYTES;
  81 }
  82
  83 static void add_early_randomness(struct hwrng *rng)
  84 {
  85         unsigned char bytes[16];
  86         int bytes_read;
  87
  88         mutex_lock(&reading_mutex);
  89         bytes_read = rng_get_data(rng, bytes, sizeof(bytes), 1);
  90         mutex_unlock(&reading_mutex);
  91         if (bytes_read > 0)
  92                 add_device_randomness(bytes, bytes_read);
  93 }
  94
  95 static inline void cleanup_rng(struct kref *kref)
  96 {
  97         struct hwrng *rng = container_of(kref, struct hwrng, ref);
  98
  99         if (rng->cleanup)
 100                 rng->cleanup(rng);
 101
 102         complete(&rng->cleanup_done);
 103 }
 104
 105 static void set_current_rng(struct hwrng *rng)
 106 {
 107         BUG_ON(!mutex_is_locked(&rng_mutex));
 108         current_rng = rng;
 109 }
 110
 111 static void drop_current_rng(void)
 112 {
 113         BUG_ON(!mutex_is_locked(&rng_mutex));
 114         if (!current_rng)
 115                 return;
 116
 117         /* decrease last reference for triggering the cleanup */
 118         kref_put(&current_rng->ref, cleanup_rng);
 119         current_rng = NULL;
 120 }
 121
 122 /* Returns ERR_PTR(), NULL or refcounted hwrng */
 123 static struct hwrng *get_current_rng(void)
 124 {
 125         struct hwrng *rng;
 126
 127         if (mutex_lock_interruptible(&rng_mutex))
 128                 return ERR_PTR(-ERESTARTSYS);
 129
 130         rng = current_rng;
 131         if (rng)
 132                 kref_get(&rng->ref);
 133
 134         mutex_unlock(&rng_mutex);
 135         return rng;
 136 }
 137
 138 static void put_rng(struct hwrng *rng)
 139 {
 140         /*
 141          * Hold rng_mutex here so we serialize in case they set_current_rng
 142          * on rng again immediately.
 143          */
 144         mutex_lock(&rng_mutex);
 145         if (rng)
 146                 kref_put(&rng->ref, cleanup_rng);
 147         mutex_unlock(&rng_mutex);
 148 }
 149
 150 static inline int hwrng_init(struct hwrng *rng)
 151 {
 152         if (kref_get_unless_zero(&rng->ref))
 153                 goto skip_init;
 154
 155         if (rng->init) {
 156                 int ret;
 157
 158                 ret =  rng->init(rng);
 159                 if (ret)
 160                         return ret;
 161         }
 162
 163         kref_init(&rng->ref);
 164         reinit_completion(&rng->cleanup_done);
 165
 166 skip_init:
 167         add_early_randomness(rng);
 168
 169         current_quality = rng->quality ? : default_quality;
 170         current_quality &= 1023;
 171
 172         if (current_quality == 0 && hwrng_fill)
 173                 kthread_stop(hwrng_fill);
 174         if (current_quality > 0 && !hwrng_fill)
 175                 start_khwrngd();
 176
 177         return 0;
 178 }
 179
 180 static int rng_dev_open(struct inode *inode, struct file *filp)
 181 {
 182         /* enforce read-only access to this chrdev */
 183         if ((filp->f_mode & FMODE_READ) == 0)
 184                 return -EINVAL;
 185         if (filp->f_mode & FMODE_WRITE)
 186                 return -EINVAL;
 187         return 0;
 188 }
 189
 190 static inline int rng_get_data(struct hwrng *rng, u8 *buffer, size_t size,
 191                         int wait) {
 192         int present;
 193
 194         BUG_ON(!mutex_is_locked(&reading_mutex));
 195         if (rng->read)
 196                 return rng->read(rng, (void *)buffer, size, wait);
 197
 198         if (rng->data_present)
 199                 present = rng->data_present(rng, wait);
 200         else
 201                 present = 1;
 202
 203         if (present)
 204                 return rng->data_read(rng, (u32 *)buffer);
 205
 206         return 0;
 207 }
 208
 209 static ssize_t rng_dev_read(struct file *filp, char __user *buf,
 210                             size_t size, loff_t *offp)
 211 {
 212         ssize_t ret = 0;
 213         int err = 0;
 214         int bytes_read, len;
 215         struct hwrng *rng;
 216
 217         while (size) {
 218                 rng = get_current_rng();
 219                 if (IS_ERR(rng)) {
 220                         err = PTR_ERR(rng);
 221                         goto out;
 222                 }
 223                 if (!rng) {
 224                         err = -ENODEV;
 225                         goto out;
 226                 }
 227
 228                 mutex_lock(&reading_mutex);
 229                 if (!data_avail) {
 230                         bytes_read = rng_get_data(rng, rng_buffer,
 231                                 rng_buffer_size(),
 232                                 !(filp->f_flags & O_NONBLOCK));
 233                         if (bytes_read < 0) {
 234                                 err = bytes_read;
 235                                 goto out_unlock_reading;
 236                         }
 237                         data_avail = bytes_read;
 238                 }
 239
 240                 if (!data_avail) {
 241                         if (filp->f_flags & O_NONBLOCK) {
 242                                 err = -EAGAIN;
 243                                 goto out_unlock_reading;
 244                         }
 245                 } else {
 246                         len = data_avail;
 247                         if (len > size)
 248                                 len = size;
 249
 250                         data_avail -= len;
 251
 252                         if (copy_to_user(buf + ret, rng_buffer + data_avail,
 253                                                                 len)) {
 254                                 err = -EFAULT;
 255                                 goto out_unlock_reading;
 256                         }
 257
 258                         size -= len;
 259                         ret += len;
 260                 }
 261
 262                 mutex_unlock(&reading_mutex);
 263                 put_rng(rng);
 264
 265                 if (need_resched())
 266                         schedule_timeout_interruptible(1);
 267
 268                 if (signal_pending(current)) {
 269                         err = -ERESTARTSYS;
 270                         goto out;
 271                 }
 272         }
 273 out:
 274         return ret ? : err;
 275
 276 out_unlock_reading:
 277         mutex_unlock(&reading_mutex);
 278         put_rng(rng);
 279         goto out;
 280 }
 281
 282
 283 static const struct file_operations rng_chrdev_ops = {
 284         .owner          = THIS_MODULE,
 285         .open           = rng_dev_open,
 286         .read           = rng_dev_read,
 287         .llseek         = noop_llseek,
 288 };
 289
 290 static struct miscdevice rng_miscdev = {
 291         .minor          = RNG_MISCDEV_MINOR,
 292         .name           = RNG_MODULE_NAME,
 293         .nodename       = "hwrng",
 294         .fops           = &rng_chrdev_ops,
 295 };
 296
 297
 298 static ssize_t hwrng_attr_current_store(struct device *dev,
 299                                         struct device_attribute *attr,
 300                                         const char *buf, size_t len)
 301 {
 302         int err;
 303         struct hwrng *rng;
 304
 305         err = mutex_lock_interruptible(&rng_mutex);
 306         if (err)
 307                 return -ERESTARTSYS;
 308         err = -ENODEV;
 309         list_for_each_entry(rng, &rng_list, list) {
 310                 if (strcmp(rng->name, buf) == 0) {
 311                         if (rng == current_rng) {
 312                                 err = 0;
 313                                 break;
 314                         }
 315                         err = hwrng_init(rng);
 316                         if (err)
 317                                 break;
 318                         drop_current_rng();
 319                         set_current_rng(rng);
 320                         err = 0;
 321                         break;
 322                 }
 323         }
 324         mutex_unlock(&rng_mutex);
 325
 326         return err ? : len;
 327 }
 328
 329 static ssize_t hwrng_attr_current_show(struct device *dev,
 330                                        struct device_attribute *attr,
 331                                        char *buf)
 332 {
 333         ssize_t ret;
 334         struct hwrng *rng;
 335
 336         rng = get_current_rng();
 337         if (IS_ERR(rng))
 338                 return PTR_ERR(rng);
 339
 340         ret = snprintf(buf, PAGE_SIZE, "%s\n", rng ? rng->name : "none");
 341         put_rng(rng);
 342
 343         return ret;
 344 }
 345
 346 static ssize_t hwrng_attr_available_show(struct device *dev,
 347                                          struct device_attribute *attr,
 348                                          char *buf)
 349 {
 350         int err;
 351         struct hwrng *rng;
 352
 353         err = mutex_lock_interruptible(&rng_mutex);
 354         if (err)
 355                 return -ERESTARTSYS;
 356         buf[0] = '\0';
 357         list_for_each_entry(rng, &rng_list, list) {
 358                 strlcat(buf, rng->name, PAGE_SIZE);
 359                 strlcat(buf, " ", PAGE_SIZE);
 360         }
 361         strlcat(buf, "\n", PAGE_SIZE);
 362         mutex_unlock(&rng_mutex);
 363
 364         return strlen(buf);
 365 }
 366
 367 static DEVICE_ATTR(rng_current, S_IRUGO | S_IWUSR,
 368                    hwrng_attr_current_show,
 369                    hwrng_attr_current_store);
 370 static DEVICE_ATTR(rng_available, S_IRUGO,
 371                    hwrng_attr_available_show,
 372                    NULL);
 373
 374
 375 static void __exit unregister_miscdev(void)
 376 {
 377         device_remove_file(rng_miscdev.this_device, &dev_attr_rng_available);
 378         device_remove_file(rng_miscdev.this_device, &dev_attr_rng_current);
 379         misc_deregister(&rng_miscdev);
 380 }
 381
 382 static int __init register_miscdev(void)
 383 {
 384         int err;
 385
 386         err = misc_register(&rng_miscdev);
 387         if (err)
 388                 goto out;
 389         err = device_create_file(rng_miscdev.this_device,
 390                                  &dev_attr_rng_current);
 391         if (err)
 392                 goto err_misc_dereg;
 393         err = device_create_file(rng_miscdev.this_device,
 394                                  &dev_attr_rng_available);
 395         if (err)
 396                 goto err_remove_current;
 397 out:
 398         return err;
 399
 400 err_remove_current:
 401         device_remove_file(rng_miscdev.this_device, &dev_attr_rng_current);
 402 err_misc_dereg:
 403         misc_deregister(&rng_miscdev);
 404         goto out;
 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         }
 431         hwrng_fill = NULL;
 432         return 0;
 433 }
 434
 435 static void start_khwrngd(void)
 436 {
 437         hwrng_fill = kthread_run(hwrng_fillfn, NULL, "hwrng");
 438         if (hwrng_fill == ERR_PTR(-ENOMEM)) {
 439                 pr_err("hwrng_fill thread creation failed");
 440                 hwrng_fill = NULL;
 441         }
 442 }
 443
 444 int hwrng_register(struct hwrng *rng)
 445 {
 446         int err = -EINVAL;
 447         struct hwrng *old_rng, *tmp;
 448
 449         if (rng->name == NULL ||
 450             (rng->data_read == NULL && rng->read == NULL))
 451                 goto out;
 452
 453         mutex_lock(&rng_mutex);
 454
 455         /* kmalloc makes this safe for virt_to_page() in virtio_rng.c */
 456         err = -ENOMEM;
 457         if (!rng_buffer) {
 458                 rng_buffer = kmalloc(rng_buffer_size(), GFP_KERNEL);
 459                 if (!rng_buffer)
 460                         goto out_unlock;
 461         }
 462         if (!rng_fillbuf) {
 463                 rng_fillbuf = kmalloc(rng_buffer_size(), GFP_KERNEL);
 464                 if (!rng_fillbuf) {
 465                         kfree(rng_buffer);
 466                         goto out_unlock;
 467                 }
 468         }
 469
 470         /* Must not register two RNGs with the same name. */
 471         err = -EEXIST;
 472         list_for_each_entry(tmp, &rng_list, list) {
 473                 if (strcmp(tmp->name, rng->name) == 0)
 474                         goto out_unlock;
 475         }
 476
 477         init_completion(&rng->cleanup_done);
 478         complete(&rng->cleanup_done);
 479
 480         old_rng = current_rng;
 481         err = 0;
 482         if (!old_rng) {
 483                 err = hwrng_init(rng);
 484                 if (err)
 485                         goto out_unlock;
 486                 set_current_rng(rng);
 487         }
 488         list_add_tail(&rng->list, &rng_list);
 489
 490         if (old_rng && !rng->init) {
 491                 /*
 492                  * Use a new device's input to add some randomness to
 493                  * the system.  If this rng device isn't going to be
 494                  * used right away, its init function hasn't been
 495                  * called yet; so only use the randomness from devices
 496                  * that don't need an init callback.
 497                  */
 498                 add_early_randomness(rng);
 499         }
 500
 501 out_unlock:
 502         mutex_unlock(&rng_mutex);
 503 out:
 504         return err;
 505 }
 506 EXPORT_SYMBOL_GPL(hwrng_register);
 507
 508 void hwrng_unregister(struct hwrng *rng)
 509 {
 510         mutex_lock(&rng_mutex);
 511
 512         list_del(&rng->list);
 513         if (current_rng == rng) {
 514                 drop_current_rng();
 515                 if (!list_empty(&rng_list)) {
 516                         struct hwrng *tail;
 517
 518                         tail = list_entry(rng_list.prev, struct hwrng, list);
 519
 520                         if (hwrng_init(tail) == 0)
 521                                 set_current_rng(tail);
 522                 }
 523         }
 524
 525         if (list_empty(&rng_list)) {
 526                 mutex_unlock(&rng_mutex);
 527                 if (hwrng_fill)
 528                         kthread_stop(hwrng_fill);
 529         } else
 530                 mutex_unlock(&rng_mutex);
 531
 532         wait_for_completion(&rng->cleanup_done);
 533 }
 534 EXPORT_SYMBOL_GPL(hwrng_unregister);
 535
 536 static int __init hwrng_modinit(void)
 537 {
 538         return register_miscdev();
 539 }
 540
 541 static void __exit hwrng_modexit(void)
 542 {
 543         mutex_lock(&rng_mutex);
 544         BUG_ON(current_rng);
 545         kfree(rng_buffer);
 546         kfree(rng_fillbuf);
 547         mutex_unlock(&rng_mutex);
 548
 549         unregister_miscdev();
 550 }
 551
 552 module_init(hwrng_modinit);
 553 module_exit(hwrng_modexit);
 554
 555 MODULE_DESCRIPTION("H/W Random Number Generator (RNG) driver");
 556 MODULE_LICENSE("GPL");