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