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 <[email protected]>
   9
  10         derived from
  11
  12         Hardware driver for the AMD 768 Random Number Generator (RNG)
  13         (c) Copyright 2001 Red Hat Inc <[email protected]>
  14
  15         derived from
  16
  17         Hardware driver for Intel i810 Random Number Generator (RNG)
  18         Copyright 2000,2001 Jeff Garzik <[email protected]>
  19         Copyright 2000,2001 Philipp Rumpf <[email protected]>
  20
  21         Added generic RNG API
  22         Copyright 2006 Michael Buesch <[email protected]>
  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/delay.h>
  42 #include <linux/slab.h>
  43 #include <linux/random.h>
  44 #include <asm/uaccess.h>
  45
  46
  47 #define RNG_MODULE_NAME         "hw_random"
  48 #define PFX                     RNG_MODULE_NAME ": "
  49 #define RNG_MISCDEV_MINOR       183 /* official */
  50
  51
  52 static struct hwrng *current_rng;
  53 static LIST_HEAD(rng_list);
  54 static DEFINE_MUTEX(rng_mutex);
  55 static int data_avail;
  56 static u8 *rng_buffer;
  57
  58 static inline int rng_get_data(struct hwrng *rng, u8 *buffer, size_t size,
  59                                int wait);
  60
  61 static size_t rng_buffer_size(void)
  62 {
  63         return SMP_CACHE_BYTES < 32 ? 32 : SMP_CACHE_BYTES;
  64 }
  65
  66 static void add_early_randomness(struct hwrng *rng)
  67 {
  68         unsigned char bytes[16];
  69         int bytes_read;
  70
  71         /*
  72          * Currently only virtio-rng cannot return data during device
  73          * probe, and that's handled in virtio-rng.c itself.  If there
  74          * are more such devices, this call to rng_get_data can be
  75          * made conditional here instead of doing it per-device.
  76          */
  77         bytes_read = rng_get_data(rng, bytes, sizeof(bytes), 1);
  78         if (bytes_read > 0)
  79                 add_device_randomness(bytes, bytes_read);
  80 }
  81
  82 static inline int hwrng_init(struct hwrng *rng)
  83 {
  84         if (rng->init) {
  85                 int ret;
  86
  87                 ret =  rng->init(rng);
  88                 if (ret)
  89                         return ret;
  90         }
  91         add_early_randomness(rng);
  92         return 0;
  93 }
  94
  95 static inline void hwrng_cleanup(struct hwrng *rng)
  96 {
  97         if (rng && rng->cleanup)
  98                 rng->cleanup(rng);
  99 }
 100
 101 static int rng_dev_open(struct inode *inode, struct file *filp)
 102 {
 103         /* enforce read-only access to this chrdev */
 104         if ((filp->f_mode & FMODE_READ) == 0)
 105                 return -EINVAL;
 106         if (filp->f_mode & FMODE_WRITE)
 107                 return -EINVAL;
 108         return 0;
 109 }
 110
 111 static inline int rng_get_data(struct hwrng *rng, u8 *buffer, size_t size,
 112                         int wait) {
 113         int present;
 114
 115         if (rng->read)
 116                 return rng->read(rng, (void *)buffer, size, wait);
 117
 118         if (rng->data_present)
 119                 present = rng->data_present(rng, wait);
 120         else
 121                 present = 1;
 122
 123         if (present)
 124                 return rng->data_read(rng, (u32 *)buffer);
 125
 126         return 0;
 127 }
 128
 129 static ssize_t rng_dev_read(struct file *filp, char __user *buf,
 130                             size_t size, loff_t *offp)
 131 {
 132         ssize_t ret = 0;
 133         int err = 0;
 134         int bytes_read, len;
 135
 136         while (size) {
 137                 if (mutex_lock_interruptible(&rng_mutex)) {
 138                         err = -ERESTARTSYS;
 139                         goto out;
 140                 }
 141
 142                 if (!current_rng) {
 143                         err = -ENODEV;
 144                         goto out_unlock;
 145                 }
 146
 147                 if (!data_avail) {
 148                         bytes_read = rng_get_data(current_rng, rng_buffer,
 149                                 rng_buffer_size(),
 150                                 !(filp->f_flags & O_NONBLOCK));
 151                         if (bytes_read < 0) {
 152                                 err = bytes_read;
 153                                 goto out_unlock;
 154                         }
 155                         data_avail = bytes_read;
 156                 }
 157
 158                 if (!data_avail) {
 159                         if (filp->f_flags & O_NONBLOCK) {
 160                                 err = -EAGAIN;
 161                                 goto out_unlock;
 162                         }
 163                 } else {
 164                         len = data_avail;
 165                         if (len > size)
 166                                 len = size;
 167
 168                         data_avail -= len;
 169
 170                         if (copy_to_user(buf + ret, rng_buffer + data_avail,
 171                                                                 len)) {
 172                                 err = -EFAULT;
 173                                 goto out_unlock;
 174                         }
 175
 176                         size -= len;
 177                         ret += len;
 178                 }
 179
 180                 mutex_unlock(&rng_mutex);
 181
 182                 if (need_resched())
 183                         schedule_timeout_interruptible(1);
 184
 185                 if (signal_pending(current)) {
 186                         err = -ERESTARTSYS;
 187                         goto out;
 188                 }
 189         }
 190 out:
 191         return ret ? : err;
 192 out_unlock:
 193         mutex_unlock(&rng_mutex);
 194         goto out;
 195 }
 196
 197
 198 static const struct file_operations rng_chrdev_ops = {
 199         .owner          = THIS_MODULE,
 200         .open           = rng_dev_open,
 201         .read           = rng_dev_read,
 202         .llseek         = noop_llseek,
 203 };
 204
 205 static struct miscdevice rng_miscdev = {
 206         .minor          = RNG_MISCDEV_MINOR,
 207         .name           = RNG_MODULE_NAME,
 208         .nodename       = "hwrng",
 209         .fops           = &rng_chrdev_ops,
 210 };
 211
 212
 213 static ssize_t hwrng_attr_current_store(struct device *dev,
 214                                         struct device_attribute *attr,
 215                                         const char *buf, size_t len)
 216 {
 217         int err;
 218         struct hwrng *rng;
 219
 220         err = mutex_lock_interruptible(&rng_mutex);
 221         if (err)
 222                 return -ERESTARTSYS;
 223         err = -ENODEV;
 224         list_for_each_entry(rng, &rng_list, list) {
 225                 if (strcmp(rng->name, buf) == 0) {
 226                         if (rng == current_rng) {
 227                                 err = 0;
 228                                 break;
 229                         }
 230                         err = hwrng_init(rng);
 231                         if (err)
 232                                 break;
 233                         hwrng_cleanup(current_rng);
 234                         current_rng = rng;
 235                         err = 0;
 236                         break;
 237                 }
 238         }
 239         mutex_unlock(&rng_mutex);
 240
 241         return err ? : len;
 242 }
 243
 244 static ssize_t hwrng_attr_current_show(struct device *dev,
 245                                        struct device_attribute *attr,
 246                                        char *buf)
 247 {
 248         int err;
 249         ssize_t ret;
 250         const char *name = "none";
 251
 252         err = mutex_lock_interruptible(&rng_mutex);
 253         if (err)
 254                 return -ERESTARTSYS;
 255         if (current_rng)
 256                 name = current_rng->name;
 257         ret = snprintf(buf, PAGE_SIZE, "%s\n", name);
 258         mutex_unlock(&rng_mutex);
 259
 260         return ret;
 261 }
 262
 263 static ssize_t hwrng_attr_available_show(struct device *dev,
 264                                          struct device_attribute *attr,
 265                                          char *buf)
 266 {
 267         int err;
 268         ssize_t ret = 0;
 269         struct hwrng *rng;
 270
 271         err = mutex_lock_interruptible(&rng_mutex);
 272         if (err)
 273                 return -ERESTARTSYS;
 274         buf[0] = '\0';
 275         list_for_each_entry(rng, &rng_list, list) {
 276                 strncat(buf, rng->name, PAGE_SIZE - ret - 1);
 277                 ret += strlen(rng->name);
 278                 strncat(buf, " ", PAGE_SIZE - ret - 1);
 279                 ret++;
 280         }
 281         strncat(buf, "\n", PAGE_SIZE - ret - 1);
 282         ret++;
 283         mutex_unlock(&rng_mutex);
 284
 285         return ret;
 286 }
 287
 288 static DEVICE_ATTR(rng_current, S_IRUGO | S_IWUSR,
 289                    hwrng_attr_current_show,
 290                    hwrng_attr_current_store);
 291 static DEVICE_ATTR(rng_available, S_IRUGO,
 292                    hwrng_attr_available_show,
 293                    NULL);
 294
 295
 296 static void unregister_miscdev(void)
 297 {
 298         device_remove_file(rng_miscdev.this_device, &dev_attr_rng_available);
 299         device_remove_file(rng_miscdev.this_device, &dev_attr_rng_current);
 300         misc_deregister(&rng_miscdev);
 301 }
 302
 303 static int register_miscdev(void)
 304 {
 305         int err;
 306
 307         err = misc_register(&rng_miscdev);
 308         if (err)
 309                 goto out;
 310         err = device_create_file(rng_miscdev.this_device,
 311                                  &dev_attr_rng_current);
 312         if (err)
 313                 goto err_misc_dereg;
 314         err = device_create_file(rng_miscdev.this_device,
 315                                  &dev_attr_rng_available);
 316         if (err)
 317                 goto err_remove_current;
 318 out:
 319         return err;
 320
 321 err_remove_current:
 322         device_remove_file(rng_miscdev.this_device, &dev_attr_rng_current);
 323 err_misc_dereg:
 324         misc_deregister(&rng_miscdev);
 325         goto out;
 326 }
 327
 328 int hwrng_register(struct hwrng *rng)
 329 {
 330         int err = -EINVAL;
 331         struct hwrng *old_rng, *tmp;
 332
 333         if (rng->name == NULL ||
 334             (rng->data_read == NULL && rng->read == NULL))
 335                 goto out;
 336
 337         mutex_lock(&rng_mutex);
 338
 339         /* kmalloc makes this safe for virt_to_page() in virtio_rng.c */
 340         err = -ENOMEM;
 341         if (!rng_buffer) {
 342                 rng_buffer = kmalloc(rng_buffer_size(), GFP_KERNEL);
 343                 if (!rng_buffer)
 344                         goto out_unlock;
 345         }
 346
 347         /* Must not register two RNGs with the same name. */
 348         err = -EEXIST;
 349         list_for_each_entry(tmp, &rng_list, list) {
 350                 if (strcmp(tmp->name, rng->name) == 0)
 351                         goto out_unlock;
 352         }
 353
 354         old_rng = current_rng;
 355         if (!old_rng) {
 356                 err = hwrng_init(rng);
 357                 if (err)
 358                         goto out_unlock;
 359                 current_rng = rng;
 360         }
 361         err = 0;
 362         if (!old_rng) {
 363                 err = register_miscdev();
 364                 if (err) {
 365                         hwrng_cleanup(rng);
 366                         current_rng = NULL;
 367                         goto out_unlock;
 368                 }
 369         }
 370         INIT_LIST_HEAD(&rng->list);
 371         list_add_tail(&rng->list, &rng_list);
 372
 373         if (old_rng && !rng->init) {
 374                 /*
 375                  * Use a new device's input to add some randomness to
 376                  * the system.  If this rng device isn't going to be
 377                  * used right away, its init function hasn't been
 378                  * called yet; so only use the randomness from devices
 379                  * that don't need an init callback.
 380                  */
 381                 add_early_randomness(rng);
 382         }
 383
 384 out_unlock:
 385         mutex_unlock(&rng_mutex);
 386 out:
 387         return err;
 388 }
 389 EXPORT_SYMBOL_GPL(hwrng_register);
 390
 391 void hwrng_unregister(struct hwrng *rng)
 392 {
 393         int err;
 394
 395         mutex_lock(&rng_mutex);
 396
 397         list_del(&rng->list);
 398         if (current_rng == rng) {
 399                 hwrng_cleanup(rng);
 400                 if (list_empty(&rng_list)) {
 401                         current_rng = NULL;
 402                 } else {
 403                         current_rng = list_entry(rng_list.prev, struct hwrng, list);
 404                         err = hwrng_init(current_rng);
 405                         if (err)
 406                                 current_rng = NULL;
 407                 }
 408         }
 409         if (list_empty(&rng_list))
 410                 unregister_miscdev();
 411
 412         mutex_unlock(&rng_mutex);
 413 }
 414 EXPORT_SYMBOL_GPL(hwrng_unregister);
 415
 416 static void __exit hwrng_exit(void)
 417 {
 418         mutex_lock(&rng_mutex);
 419         BUG_ON(current_rng);
 420         kfree(rng_buffer);
 421         mutex_unlock(&rng_mutex);
 422 }
 423
 424 module_exit(hwrng_exit);
 425
 426 MODULE_DESCRIPTION("H/W Random Number Generator (RNG) driver");
 427 MODULE_LICENSE("GPL");