drivers/usb/misc/chaoskey.c

   1 // SPDX-License-Identifier: GPL-2.0
   2 /*
   3  * chaoskey - driver for ChaosKey device from Altus Metrum.
   4  *
   5  * This device provides true random numbers using a noise source based
   6  * on a reverse-biased p-n junction in avalanche breakdown. More
   7  * details can be found at http://chaoskey.org
   8  *
   9  * The driver connects to the kernel hardware RNG interface to provide
  10  * entropy for /dev/random and other kernel activities. It also offers
  11  * a separate /dev/ entry to allow for direct access to the random
  12  * bit stream.
  13  *
  14  * Copyright © 2015 Keith Packard <keithp@keithp.com>
  15  */
  16
  17 #include <linux/module.h>
  18 #include <linux/slab.h>
  19 #include <linux/usb.h>
  20 #include <linux/wait.h>
  21 #include <linux/hw_random.h>
  22 #include <linux/mutex.h>
  23 #include <linux/uaccess.h>
  24
  25 static struct usb_driver chaoskey_driver;
  26 static struct usb_class_driver chaoskey_class;
  27 static int chaoskey_rng_read(struct hwrng *rng, void *data,
  28                              size_t max, bool wait);
  29
  30 #define usb_dbg(usb_if, format, arg...) \
  31         dev_dbg(&(usb_if)->dev, format, ## arg)
  32
  33 #define usb_err(usb_if, format, arg...) \
  34         dev_err(&(usb_if)->dev, format, ## arg)
  35
  36 /* Version Information */
  37 #define DRIVER_AUTHOR   "Keith Packard, keithp@keithp.com"
  38 #define DRIVER_DESC     "Altus Metrum ChaosKey driver"
  39 #define DRIVER_SHORT    "chaoskey"
  40
  41 MODULE_AUTHOR(DRIVER_AUTHOR);
  42 MODULE_DESCRIPTION(DRIVER_DESC);
  43 MODULE_LICENSE("GPL");
  44
  45 #define CHAOSKEY_VENDOR_ID      0x1d50  /* OpenMoko */
  46 #define CHAOSKEY_PRODUCT_ID     0x60c6  /* ChaosKey */
  47
  48 #define ALEA_VENDOR_ID          0x12d8  /* Araneus */
  49 #define ALEA_PRODUCT_ID         0x0001  /* Alea I */
  50
  51 #define CHAOSKEY_BUF_LEN        64      /* max size of USB full speed packet */
  52
  53 #define NAK_TIMEOUT (HZ)                /* normal stall/wait timeout */
  54 #define ALEA_FIRST_TIMEOUT (HZ*3)       /* first stall/wait timeout for Alea */
  55
  56 #ifdef CONFIG_USB_DYNAMIC_MINORS
  57 #define USB_CHAOSKEY_MINOR_BASE 0
  58 #else
  59
  60 /* IOWARRIOR_MINOR_BASE + 16, not official yet */
  61 #define USB_CHAOSKEY_MINOR_BASE 224
  62 #endif
  63
  64 static const struct usb_device_id chaoskey_table[] = {
  65         { USB_DEVICE(CHAOSKEY_VENDOR_ID, CHAOSKEY_PRODUCT_ID) },
  66         { USB_DEVICE(ALEA_VENDOR_ID, ALEA_PRODUCT_ID) },
  67         { },
  68 };
  69 MODULE_DEVICE_TABLE(usb, chaoskey_table);
  70
  71 static void chaos_read_callback(struct urb *urb);
  72
  73 /* Driver-local specific stuff */
  74 struct chaoskey {
  75         struct usb_interface *interface;
  76         char in_ep;
  77         struct mutex lock;
  78         struct mutex rng_lock;
  79         int open;                       /* open count */
  80         bool present;                   /* device not disconnected */
  81         bool reading;                   /* ongoing IO */
  82         bool reads_started;             /* track first read for Alea */
  83         int size;                       /* size of buf */
  84         int valid;                      /* bytes of buf read */
  85         int used;                       /* bytes of buf consumed */
  86         char *name;                     /* product + serial */
  87         struct hwrng hwrng;             /* Embedded struct for hwrng */
  88         int hwrng_registered;           /* registered with hwrng API */
  89         wait_queue_head_t wait_q;       /* for timeouts */
  90         struct urb *urb;                /* for performing IO */
  91         char *buf;
  92 };
  93
  94 static void chaoskey_free(struct chaoskey *dev)
  95 {
  96         if (dev) {
  97                 usb_dbg(dev->interface, "free");
  98                 usb_free_urb(dev->urb);
  99                 kfree(dev->name);
 100                 kfree(dev->buf);
 101                 kfree(dev);
 102         }
 103 }
 104
 105 static int chaoskey_probe(struct usb_interface *interface,
 106                           const struct usb_device_id *id)
 107 {
 108         struct usb_device *udev = interface_to_usbdev(interface);
 109         struct usb_host_interface *altsetting = interface->cur_altsetting;
 110         struct usb_endpoint_descriptor *epd;
 111         int in_ep;
 112         struct chaoskey *dev;
 113         int result = -ENOMEM;
 114         int size;
 115         int res;
 116
 117         usb_dbg(interface, "probe %s-%s", udev->product, udev->serial);
 118
 119         /* Find the first bulk IN endpoint and its packet size */
 120         res = usb_find_bulk_in_endpoint(altsetting, &epd);
 121         if (res) {
 122                 usb_dbg(interface, "no IN endpoint found");
 123                 return res;
 124         }
 125
 126         in_ep = usb_endpoint_num(epd);
 127         size = usb_endpoint_maxp(epd);
 128
 129         /* Validate endpoint and size */
 130         if (size <= 0) {
 131                 usb_dbg(interface, "invalid size (%d)", size);
 132                 return -ENODEV;
 133         }
 134
 135         if (size > CHAOSKEY_BUF_LEN) {
 136                 usb_dbg(interface, "size reduced from %d to %d\n",
 137                         size, CHAOSKEY_BUF_LEN);
 138                 size = CHAOSKEY_BUF_LEN;
 139         }
 140
 141         /* Looks good, allocate and initialize */
 142
 143         dev = kzalloc(sizeof(struct chaoskey), GFP_KERNEL);
 144
 145         if (dev == NULL)
 146                 goto out;
 147
 148         dev->buf = kmalloc(size, GFP_KERNEL);
 149
 150         if (dev->buf == NULL)
 151                 goto out;
 152
 153         dev->urb = usb_alloc_urb(0, GFP_KERNEL);
 154
 155         if (!dev->urb)
 156                 goto out;
 157
 158         usb_fill_bulk_urb(dev->urb,
 159                 udev,
 160                 usb_rcvbulkpipe(udev, in_ep),
 161                 dev->buf,
 162                 size,
 163                 chaos_read_callback,
 164                 dev);
 165
 166         /* Construct a name using the product and serial values. Each
 167          * device needs a unique name for the hwrng code
 168          */
 169
 170         if (udev->product && udev->serial) {
 171                 dev->name = kasprintf(GFP_KERNEL, "%s-%s", udev->product,
 172                                       udev->serial);
 173                 if (dev->name == NULL)
 174                         goto out;
 175         }
 176
 177         dev->interface = interface;
 178
 179         dev->in_ep = in_ep;
 180
 181         if (le16_to_cpu(udev->descriptor.idVendor) != ALEA_VENDOR_ID)
 182                 dev->reads_started = true;
 183
 184         dev->size = size;
 185         dev->present = true;
 186
 187         init_waitqueue_head(&dev->wait_q);
 188
 189         mutex_init(&dev->lock);
 190         mutex_init(&dev->rng_lock);
 191
 192         usb_set_intfdata(interface, dev);
 193
 194         result = usb_register_dev(interface, &chaoskey_class);
 195         if (result) {
 196                 usb_err(interface, "Unable to allocate minor number.");
 197                 goto out;
 198         }
 199
 200         dev->hwrng.name = dev->name ? dev->name : chaoskey_driver.name;
 201         dev->hwrng.read = chaoskey_rng_read;
 202         dev->hwrng.quality = 1024;
 203
 204         dev->hwrng_registered = (hwrng_register(&dev->hwrng) == 0);
 205         if (!dev->hwrng_registered)
 206                 usb_err(interface, "Unable to register with hwrng");
 207
 208         usb_enable_autosuspend(udev);
 209
 210         usb_dbg(interface, "chaoskey probe success, size %d", dev->size);
 211         return 0;
 212
 213 out:
 214         usb_set_intfdata(interface, NULL);
 215         chaoskey_free(dev);
 216         return result;
 217 }
 218
 219 static void chaoskey_disconnect(struct usb_interface *interface)
 220 {
 221         struct chaoskey *dev;
 222
 223         usb_dbg(interface, "disconnect");
 224         dev = usb_get_intfdata(interface);
 225         if (!dev) {
 226                 usb_dbg(interface, "disconnect failed - no dev");
 227                 return;
 228         }
 229
 230         if (dev->hwrng_registered)
 231                 hwrng_unregister(&dev->hwrng);
 232
 233         usb_deregister_dev(interface, &chaoskey_class);
 234
 235         usb_set_intfdata(interface, NULL);
 236         mutex_lock(&dev->lock);
 237
 238         dev->present = false;
 239         usb_poison_urb(dev->urb);
 240
 241         if (!dev->open) {
 242                 mutex_unlock(&dev->lock);
 243                 chaoskey_free(dev);
 244         } else
 245                 mutex_unlock(&dev->lock);
 246
 247         usb_dbg(interface, "disconnect done");
 248 }
 249
 250 static int chaoskey_open(struct inode *inode, struct file *file)
 251 {
 252         struct chaoskey *dev;
 253         struct usb_interface *interface;
 254
 255         /* get the interface from minor number and driver information */
 256         interface = usb_find_interface(&chaoskey_driver, iminor(inode));
 257         if (!interface)
 258                 return -ENODEV;
 259
 260         usb_dbg(interface, "open");
 261
 262         dev = usb_get_intfdata(interface);
 263         if (!dev) {
 264                 usb_dbg(interface, "open (dev)");
 265                 return -ENODEV;
 266         }
 267
 268         file->private_data = dev;
 269         mutex_lock(&dev->lock);
 270         ++dev->open;
 271         mutex_unlock(&dev->lock);
 272
 273         usb_dbg(interface, "open success");
 274         return 0;
 275 }
 276
 277 static int chaoskey_release(struct inode *inode, struct file *file)
 278 {
 279         struct chaoskey *dev = file->private_data;
 280         struct usb_interface *interface;
 281
 282         if (dev == NULL)
 283                 return -ENODEV;
 284
 285         interface = dev->interface;
 286
 287         usb_dbg(interface, "release");
 288
 289         mutex_lock(&dev->lock);
 290
 291         usb_dbg(interface, "open count at release is %d", dev->open);
 292
 293         if (dev->open <= 0) {
 294                 usb_dbg(interface, "invalid open count (%d)", dev->open);
 295                 mutex_unlock(&dev->lock);
 296                 return -ENODEV;
 297         }
 298
 299         --dev->open;
 300
 301         if (!dev->present) {
 302                 if (dev->open == 0) {
 303                         mutex_unlock(&dev->lock);
 304                         chaoskey_free(dev);
 305                 } else
 306                         mutex_unlock(&dev->lock);
 307         } else
 308                 mutex_unlock(&dev->lock);
 309
 310         usb_dbg(interface, "release success");
 311         return 0;
 312 }
 313
 314 static void chaos_read_callback(struct urb *urb)
 315 {
 316         struct chaoskey *dev = urb->context;
 317         int status = urb->status;
 318
 319         usb_dbg(dev->interface, "callback status (%d)", status);
 320
 321         if (status == 0)
 322                 dev->valid = urb->actual_length;
 323         else
 324                 dev->valid = 0;
 325
 326         dev->used = 0;
 327
 328         /* must be seen first before validity is announced */
 329         smp_wmb();
 330
 331         dev->reading = false;
 332         wake_up(&dev->wait_q);
 333 }
 334
 335 /* Fill the buffer. Called with dev->lock held
 336  */
 337 static int _chaoskey_fill(struct chaoskey *dev)
 338 {
 339         DEFINE_WAIT(wait);
 340         int result;
 341         bool started;
 342
 343         usb_dbg(dev->interface, "fill");
 344
 345         /* Return immediately if someone called before the buffer was
 346          * empty */
 347         if (dev->valid != dev->used) {
 348                 usb_dbg(dev->interface, "not empty yet (valid %d used %d)",
 349                         dev->valid, dev->used);
 350                 return 0;
 351         }
 352
 353         /* Bail if the device has been removed */
 354         if (!dev->present) {
 355                 usb_dbg(dev->interface, "device not present");
 356                 return -ENODEV;
 357         }
 358
 359         /* Make sure the device is awake */
 360         result = usb_autopm_get_interface(dev->interface);
 361         if (result) {
 362                 usb_dbg(dev->interface, "wakeup failed (result %d)", result);
 363                 return result;
 364         }
 365
 366         dev->reading = true;
 367         result = usb_submit_urb(dev->urb, GFP_KERNEL);
 368         if (result < 0) {
 369                 result = usb_translate_errors(result);
 370                 dev->reading = false;
 371                 goto out;
 372         }
 373
 374         /* The first read on the Alea takes a little under 2 seconds.
 375          * Reads after the first read take only a few microseconds
 376          * though.  Presumably the entropy-generating circuit needs
 377          * time to ramp up.  So, we wait longer on the first read.
 378          */
 379         started = dev->reads_started;
 380         dev->reads_started = true;
 381         result = wait_event_interruptible_timeout(
 382                 dev->wait_q,
 383                 !dev->reading,
 384                 (started ? NAK_TIMEOUT : ALEA_FIRST_TIMEOUT) );
 385
 386         if (result < 0)
 387                 goto out;
 388
 389         if (result == 0)
 390                 result = -ETIMEDOUT;
 391         else
 392                 result = dev->valid;
 393 out:
 394         /* Let the device go back to sleep eventually */
 395         usb_autopm_put_interface(dev->interface);
 396
 397         usb_dbg(dev->interface, "read %d bytes", dev->valid);
 398
 399         return result;
 400 }
 401
 402 static ssize_t chaoskey_read(struct file *file,
 403                              char __user *buffer,
 404                              size_t count,
 405                              loff_t *ppos)
 406 {
 407         struct chaoskey *dev;
 408         ssize_t read_count = 0;
 409         int this_time;
 410         int result = 0;
 411         unsigned long remain;
 412
 413         dev = file->private_data;
 414
 415         if (dev == NULL || !dev->present)
 416                 return -ENODEV;
 417
 418         usb_dbg(dev->interface, "read %zu", count);
 419
 420         while (count > 0) {
 421
 422                 /* Grab the rng_lock briefly to ensure that the hwrng interface
 423                  * gets priority over other user access
 424                  */
 425                 result = mutex_lock_interruptible(&dev->rng_lock);
 426                 if (result)
 427                         goto bail;
 428                 mutex_unlock(&dev->rng_lock);
 429
 430                 result = mutex_lock_interruptible(&dev->lock);
 431                 if (result)
 432                         goto bail;
 433                 if (dev->valid == dev->used) {
 434                         result = _chaoskey_fill(dev);
 435                         if (result < 0) {
 436                                 mutex_unlock(&dev->lock);
 437                                 goto bail;
 438                         }
 439                 }
 440
 441                 this_time = dev->valid - dev->used;
 442                 if (this_time > count)
 443                         this_time = count;
 444
 445                 remain = copy_to_user(buffer, dev->buf + dev->used, this_time);
 446                 if (remain) {
 447                         result = -EFAULT;
 448
 449                         /* Consume the bytes that were copied so we don't leak
 450                          * data to user space
 451                          */
 452                         dev->used += this_time - remain;
 453                         mutex_unlock(&dev->lock);
 454                         goto bail;
 455                 }
 456
 457                 count -= this_time;
 458                 read_count += this_time;
 459                 buffer += this_time;
 460                 dev->used += this_time;
 461                 mutex_unlock(&dev->lock);
 462         }
 463 bail:
 464         if (read_count) {
 465                 usb_dbg(dev->interface, "read %zu bytes", read_count);
 466                 return read_count;
 467         }
 468         usb_dbg(dev->interface, "empty read, result %d", result);
 469         if (result == -ETIMEDOUT)
 470                 result = -EAGAIN;
 471         return result;
 472 }
 473
 474 static int chaoskey_rng_read(struct hwrng *rng, void *data,
 475                              size_t max, bool wait)
 476 {
 477         struct chaoskey *dev = container_of(rng, struct chaoskey, hwrng);
 478         int this_time;
 479
 480         usb_dbg(dev->interface, "rng_read max %zu wait %d", max, wait);
 481
 482         if (!dev->present) {
 483                 usb_dbg(dev->interface, "device not present");
 484                 return 0;
 485         }
 486
 487         /* Hold the rng_lock until we acquire the device lock so that
 488          * this operation gets priority over other user access to the
 489          * device
 490          */
 491         mutex_lock(&dev->rng_lock);
 492
 493         mutex_lock(&dev->lock);
 494
 495         mutex_unlock(&dev->rng_lock);
 496
 497         /* Try to fill the buffer if empty. It doesn't actually matter
 498          * if _chaoskey_fill works; we'll just return zero bytes as
 499          * the buffer will still be empty
 500          */
 501         if (dev->valid == dev->used)
 502                 (void) _chaoskey_fill(dev);
 503
 504         this_time = dev->valid - dev->used;
 505         if (this_time > max)
 506                 this_time = max;
 507
 508         memcpy(data, dev->buf + dev->used, this_time);
 509
 510         dev->used += this_time;
 511
 512         mutex_unlock(&dev->lock);
 513
 514         usb_dbg(dev->interface, "rng_read this_time %d\n", this_time);
 515         return this_time;
 516 }
 517
 518 #ifdef CONFIG_PM
 519 static int chaoskey_suspend(struct usb_interface *interface,
 520                             pm_message_t message)
 521 {
 522         usb_dbg(interface, "suspend");
 523         return 0;
 524 }
 525
 526 static int chaoskey_resume(struct usb_interface *interface)
 527 {
 528         usb_dbg(interface, "resume");
 529         return 0;
 530 }
 531 #else
 532 #define chaoskey_suspend NULL
 533 #define chaoskey_resume NULL
 534 #endif
 535
 536 /* file operation pointers */
 537 static const struct file_operations chaoskey_fops = {
 538         .owner = THIS_MODULE,
 539         .read = chaoskey_read,
 540         .open = chaoskey_open,
 541         .release = chaoskey_release,
 542         .llseek = default_llseek,
 543 };
 544
 545 /* class driver information */
 546 static struct usb_class_driver chaoskey_class = {
 547         .name = "chaoskey%d",
 548         .fops = &chaoskey_fops,
 549         .minor_base = USB_CHAOSKEY_MINOR_BASE,
 550 };
 551
 552 /* usb specific object needed to register this driver with the usb subsystem */
 553 static struct usb_driver chaoskey_driver = {
 554         .name = DRIVER_SHORT,
 555         .probe = chaoskey_probe,
 556         .disconnect = chaoskey_disconnect,
 557         .suspend = chaoskey_suspend,
 558         .resume = chaoskey_resume,
 559         .reset_resume = chaoskey_resume,
 560         .id_table = chaoskey_table,
 561         .supports_autosuspend = 1,
 562 };
 563
 564 module_usb_driver(chaoskey_driver);
 565