drivers/char/hw_random/core.c

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