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 <asm/uaccess.h>
  46
  47
  48 #define RNG_MODULE_NAME         "hw_random"
  49 #define PFX                     RNG_MODULE_NAME ": "
  50 #define RNG_MISCDEV_MINOR       183 /* official */
  51
  52
  53 static struct hwrng *current_rng;
  54 static struct task_struct *hwrng_fill;
  55 static LIST_HEAD(rng_list);
  56 static DEFINE_MUTEX(rng_mutex);
  57 static int data_avail;
  58 static u8 *rng_buffer, *rng_fillbuf;
  59 static unsigned short current_quality;
  60 static unsigned short default_quality; /* = 0; default to "off" */
  61
  62 module_param(current_quality, ushort, 0644);
  63 MODULE_PARM_DESC(current_quality,
  64                  "current hwrng entropy estimation per mill");
  65 module_param(default_quality, ushort, 0644);
  66 MODULE_PARM_DESC(default_quality,
  67                  "default entropy content of hwrng per mill");
  68
  69 static void start_khwrngd(void);
  70
  71 static inline int rng_get_data(struct hwrng *rng, u8 *buffer, size_t size,
  72                                int wait);
  73
  74 static size_t rng_buffer_size(void)
  75 {
  76         return SMP_CACHE_BYTES < 32 ? 32 : SMP_CACHE_BYTES;
  77 }
  78
  79 static void add_early_randomness(struct hwrng *rng)
  80 {
  81         unsigned char bytes[16];
  82         int bytes_read;
  83
  84         /*
  85          * Currently only virtio-rng cannot return data during device
  86          * probe, and that's handled in virtio-rng.c itself.  If there
  87          * are more such devices, this call to rng_get_data can be
  88          * made conditional here instead of doing it per-device.
  89          */
  90         bytes_read = rng_get_data(rng, bytes, sizeof(bytes), 1);
  91         if (bytes_read > 0)
  92                 add_device_randomness(bytes, bytes_read);
  93 }
  94
  95 static inline int hwrng_init(struct hwrng *rng)
  96 {
  97         if (rng->init) {
  98                 int ret;
  99
 100                 ret =  rng->init(rng);
 101                 if (ret)
 102                         return ret;
 103         }
 104         add_early_randomness(rng);
 105
 106         current_quality = rng->quality ? : default_quality;
 107         current_quality &= 1023;
 108
 109         if (current_quality == 0 && hwrng_fill)
 110                 kthread_stop(hwrng_fill);
 111         if (current_quality > 0 && !hwrng_fill)
 112                 start_khwrngd();
 113
 114         return 0;
 115 }
 116
 117 static inline void hwrng_cleanup(struct hwrng *rng)
 118 {
 119         if (rng && rng->cleanup)
 120                 rng->cleanup(rng);
 121 }
 122
 123 static int rng_dev_open(struct inode *inode, struct file *filp)
 124 {
 125         /* enforce read-only access to this chrdev */
 126         if ((filp->f_mode & FMODE_READ) == 0)
 127                 return -EINVAL;
 128         if (filp->f_mode & FMODE_WRITE)
 129                 return -EINVAL;
 130         return 0;
 131 }
 132
 133 static inline int rng_get_data(struct hwrng *rng, u8 *buffer, size_t size,
 134                         int wait) {
 135         int present;
 136
 137         if (rng->read)
 138                 return rng->read(rng, (void *)buffer, size, wait);
 139
 140         if (rng->data_present)
 141                 present = rng->data_present(rng, wait);
 142         else
 143                 present = 1;
 144
 145         if (present)
 146                 return rng->data_read(rng, (u32 *)buffer);
 147
 148         return 0;
 149 }
 150
 151 static ssize_t rng_dev_read(struct file *filp, char __user *buf,
 152                             size_t size, loff_t *offp)
 153 {
 154         ssize_t ret = 0;
 155         int err = 0;
 156         int bytes_read, len;
 157
 158         while (size) {
 159                 if (mutex_lock_interruptible(&rng_mutex)) {
 160                         err = -ERESTARTSYS;
 161                         goto out;
 162                 }
 163
 164                 if (!current_rng) {
 165                         err = -ENODEV;
 166                         goto out_unlock;
 167                 }
 168
 169                 if (!data_avail) {
 170                         bytes_read = rng_get_data(current_rng, rng_buffer,
 171                                 rng_buffer_size(),
 172                                 !(filp->f_flags & O_NONBLOCK));
 173                         if (bytes_read < 0) {
 174                                 err = bytes_read;
 175                                 goto out_unlock;
 176                         }
 177                         data_avail = bytes_read;
 178                 }
 179
 180                 if (!data_avail) {
 181                         if (filp->f_flags & O_NONBLOCK) {
 182                                 err = -EAGAIN;
 183                                 goto out_unlock;
 184                         }
 185                 } else {
 186                         len = data_avail;
 187                         if (len > size)
 188                                 len = size;
 189
 190                         data_avail -= len;
 191
 192                         if (copy_to_user(buf + ret, rng_buffer + data_avail,
 193                                                                 len)) {
 194                                 err = -EFAULT;
 195                                 goto out_unlock;
 196                         }
 197
 198                         size -= len;
 199                         ret += len;
 200                 }
 201
 202                 mutex_unlock(&rng_mutex);
 203
 204                 if (need_resched())
 205                         schedule_timeout_interruptible(1);
 206
 207                 if (signal_pending(current)) {
 208                         err = -ERESTARTSYS;
 209                         goto out;
 210                 }
 211         }
 212 out:
 213         return ret ? : err;
 214 out_unlock:
 215         mutex_unlock(&rng_mutex);
 216         goto out;
 217 }
 218
 219
 220 static const struct file_operations rng_chrdev_ops = {
 221         .owner          = THIS_MODULE,
 222         .open           = rng_dev_open,
 223         .read           = rng_dev_read,
 224         .llseek         = noop_llseek,
 225 };
 226
 227 static struct miscdevice rng_miscdev = {
 228         .minor          = RNG_MISCDEV_MINOR,
 229         .name           = RNG_MODULE_NAME,
 230         .nodename       = "hwrng",
 231         .fops           = &rng_chrdev_ops,
 232 };
 233
 234
 235 static ssize_t hwrng_attr_current_store(struct device *dev,
 236                                         struct device_attribute *attr,
 237                                         const char *buf, size_t len)
 238 {
 239         int err;
 240         struct hwrng *rng;
 241
 242         err = mutex_lock_interruptible(&rng_mutex);
 243         if (err)
 244                 return -ERESTARTSYS;
 245         err = -ENODEV;
 246         list_for_each_entry(rng, &rng_list, list) {
 247                 if (strcmp(rng->name, buf) == 0) {
 248                         if (rng == current_rng) {
 249                                 err = 0;
 250                                 break;
 251                         }
 252                         err = hwrng_init(rng);
 253                         if (err)
 254                                 break;
 255                         hwrng_cleanup(current_rng);
 256                         current_rng = rng;
 257                         err = 0;
 258                         break;
 259                 }
 260         }
 261         mutex_unlock(&rng_mutex);
 262
 263         return err ? : len;
 264 }
 265
 266 static ssize_t hwrng_attr_current_show(struct device *dev,
 267                                        struct device_attribute *attr,
 268                                        char *buf)
 269 {
 270         int err;
 271         ssize_t ret;
 272         const char *name = "none";
 273
 274         err = mutex_lock_interruptible(&rng_mutex);
 275         if (err)
 276                 return -ERESTARTSYS;
 277         if (current_rng)
 278                 name = current_rng->name;
 279         ret = snprintf(buf, PAGE_SIZE, "%s\n", name);
 280         mutex_unlock(&rng_mutex);
 281
 282         return ret;
 283 }
 284
 285 static ssize_t hwrng_attr_available_show(struct device *dev,
 286                                          struct device_attribute *attr,
 287                                          char *buf)
 288 {
 289         int err;
 290         ssize_t ret = 0;
 291         struct hwrng *rng;
 292
 293         err = mutex_lock_interruptible(&rng_mutex);
 294         if (err)
 295                 return -ERESTARTSYS;
 296         buf[0] = '\0';
 297         list_for_each_entry(rng, &rng_list, list) {
 298                 strncat(buf, rng->name, PAGE_SIZE - ret - 1);
 299                 ret += strlen(rng->name);
 300                 strncat(buf, " ", PAGE_SIZE - ret - 1);
 301                 ret++;
 302         }
 303         strncat(buf, "\n", PAGE_SIZE - ret - 1);
 304         ret++;
 305         mutex_unlock(&rng_mutex);
 306
 307         return ret;
 308 }
 309
 310 static DEVICE_ATTR(rng_current, S_IRUGO | S_IWUSR,
 311                    hwrng_attr_current_show,
 312                    hwrng_attr_current_store);
 313 static DEVICE_ATTR(rng_available, S_IRUGO,
 314                    hwrng_attr_available_show,
 315                    NULL);
 316
 317
 318 static void unregister_miscdev(void)
 319 {
 320         device_remove_file(rng_miscdev.this_device, &dev_attr_rng_available);
 321         device_remove_file(rng_miscdev.this_device, &dev_attr_rng_current);
 322         misc_deregister(&rng_miscdev);
 323 }
 324
 325 static int register_miscdev(void)
 326 {
 327         int err;
 328
 329         err = misc_register(&rng_miscdev);
 330         if (err)
 331                 goto out;
 332         err = device_create_file(rng_miscdev.this_device,
 333                                  &dev_attr_rng_current);
 334         if (err)
 335                 goto err_misc_dereg;
 336         err = device_create_file(rng_miscdev.this_device,
 337                                  &dev_attr_rng_available);
 338         if (err)
 339                 goto err_remove_current;
 340 out:
 341         return err;
 342
 343 err_remove_current:
 344         device_remove_file(rng_miscdev.this_device, &dev_attr_rng_current);
 345 err_misc_dereg:
 346         misc_deregister(&rng_miscdev);
 347         goto out;
 348 }
 349
 350 static int hwrng_fillfn(void *unused)
 351 {
 352         long rc;
 353
 354         while (!kthread_should_stop()) {
 355                 if (!current_rng)
 356                         break;
 357                 rc = rng_get_data(current_rng, rng_fillbuf,
 358                                   rng_buffer_size(), 1);
 359                 if (rc <= 0) {
 360                         pr_warn("hwrng: no data available\n");
 361                         msleep_interruptible(10000);
 362                         continue;
 363                 }
 364                 add_hwgenerator_randomness((void *)rng_fillbuf, rc,
 365                                            rc * current_quality * 8 >> 10);
 366         }
 367         hwrng_fill = NULL;
 368         return 0;
 369 }
 370
 371 static void start_khwrngd(void)
 372 {
 373         hwrng_fill = kthread_run(hwrng_fillfn, NULL, "hwrng");
 374         if (hwrng_fill == ERR_PTR(-ENOMEM)) {
 375                 pr_err("hwrng_fill thread creation failed");
 376                 hwrng_fill = NULL;
 377         }
 378 }
 379
 380 int hwrng_register(struct hwrng *rng)
 381 {
 382         int err = -EINVAL;
 383         struct hwrng *old_rng, *tmp;
 384
 385         if (rng->name == NULL ||
 386             (rng->data_read == NULL && rng->read == NULL))
 387                 goto out;
 388
 389         mutex_lock(&rng_mutex);
 390
 391         /* kmalloc makes this safe for virt_to_page() in virtio_rng.c */
 392         err = -ENOMEM;
 393         if (!rng_buffer) {
 394                 rng_buffer = kmalloc(rng_buffer_size(), GFP_KERNEL);
 395                 if (!rng_buffer)
 396                         goto out_unlock;
 397         }
 398         if (!rng_fillbuf) {
 399                 rng_fillbuf = kmalloc(rng_buffer_size(), GFP_KERNEL);
 400                 if (!rng_fillbuf) {
 401                         kfree(rng_buffer);
 402                         goto out_unlock;
 403                 }
 404         }
 405
 406         /* Must not register two RNGs with the same name. */
 407         err = -EEXIST;
 408         list_for_each_entry(tmp, &rng_list, list) {
 409                 if (strcmp(tmp->name, rng->name) == 0)
 410                         goto out_unlock;
 411         }
 412
 413         old_rng = current_rng;
 414         if (!old_rng) {
 415                 err = hwrng_init(rng);
 416                 if (err)
 417                         goto out_unlock;
 418                 current_rng = rng;
 419         }
 420         err = 0;
 421         if (!old_rng) {
 422                 err = register_miscdev();
 423                 if (err) {
 424                         hwrng_cleanup(rng);
 425                         current_rng = NULL;
 426                         goto out_unlock;
 427                 }
 428         }
 429         INIT_LIST_HEAD(&rng->list);
 430         list_add_tail(&rng->list, &rng_list);
 431
 432         if (old_rng && !rng->init) {
 433                 /*
 434                  * Use a new device's input to add some randomness to
 435                  * the system.  If this rng device isn't going to be
 436                  * used right away, its init function hasn't been
 437                  * called yet; so only use the randomness from devices
 438                  * that don't need an init callback.
 439                  */
 440                 add_early_randomness(rng);
 441         }
 442
 443 out_unlock:
 444         mutex_unlock(&rng_mutex);
 445 out:
 446         return err;
 447 }
 448 EXPORT_SYMBOL_GPL(hwrng_register);
 449
 450 void hwrng_unregister(struct hwrng *rng)
 451 {
 452         int err;
 453
 454         mutex_lock(&rng_mutex);
 455
 456         list_del(&rng->list);
 457         if (current_rng == rng) {
 458                 hwrng_cleanup(rng);
 459                 if (list_empty(&rng_list)) {
 460                         current_rng = NULL;
 461                 } else {
 462                         current_rng = list_entry(rng_list.prev, struct hwrng, list);
 463                         err = hwrng_init(current_rng);
 464                         if (err)
 465                                 current_rng = NULL;
 466                 }
 467         }
 468         if (list_empty(&rng_list)) {
 469                 unregister_miscdev();
 470                 if (hwrng_fill)
 471                         kthread_stop(hwrng_fill);
 472         }
 473
 474         mutex_unlock(&rng_mutex);
 475 }
 476 EXPORT_SYMBOL_GPL(hwrng_unregister);
 477
 478 static void __exit hwrng_exit(void)
 479 {
 480         mutex_lock(&rng_mutex);
 481         BUG_ON(current_rng);
 482         kfree(rng_buffer);
 483         kfree(rng_fillbuf);
 484         mutex_unlock(&rng_mutex);
 485 }
 486
 487 module_exit(hwrng_exit);
 488
 489 MODULE_DESCRIPTION("H/W Random Number Generator (RNG) driver");
 490 MODULE_LICENSE("GPL");