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