drivers/xen/gntalloc.c

   1 /******************************************************************************
   2  * gntalloc.c
   3  *
   4  * Device for creating grant references (in user-space) that may be shared
   5  * with other domains.
   6  *
   7  * This program is distributed in the hope that it will be useful,
   8  * but WITHOUT ANY WARRANTY; without even the implied warranty of
   9  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  10  * GNU General Public License for more details.
  11  *
  12  * You should have received a copy of the GNU General Public License
  13  * along with this program; if not, write to the Free Software
  14  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  15  */
  16
  17 /*
  18  * This driver exists to allow userspace programs in Linux to allocate kernel
  19  * memory that will later be shared with another domain.  Without this device,
  20  * Linux userspace programs cannot create grant references.
  21  *
  22  * How this stuff works:
  23  *   X -> granting a page to Y
  24  *   Y -> mapping the grant from X
  25  *
  26  *   1. X uses the gntalloc device to allocate a page of kernel memory, P.
  27  *   2. X creates an entry in the grant table that says domid(Y) can access P.
  28  *      This is done without a hypercall unless the grant table needs expansion.
  29  *   3. X gives the grant reference identifier, GREF, to Y.
  30  *   4. Y maps the page, either directly into kernel memory for use in a backend
  31  *      driver, or via a the gntdev device to map into the address space of an
  32  *      application running in Y. This is the first point at which Xen does any
  33  *      tracking of the page.
  34  *   5. A program in X mmap()s a segment of the gntalloc device that corresponds
  35  *      to the shared page, and can now communicate with Y over the shared page.
  36  *
  37  *
  38  * NOTE TO USERSPACE LIBRARIES:
  39  *   The grant allocation and mmap()ing are, naturally, two separate operations.
  40  *   You set up the sharing by calling the create ioctl() and then the mmap().
  41  *   Teardown requires munmap() and either close() or ioctl().
  42  *
  43  * WARNING: Since Xen does not allow a guest to forcibly end the use of a grant
  44  * reference, this device can be used to consume kernel memory by leaving grant
  45  * references mapped by another domain when an application exits. Therefore,
  46  * there is a global limit on the number of pages that can be allocated. When
  47  * all references to the page are unmapped, it will be freed during the next
  48  * grant operation.
  49  */
  50
  51 #define pr_fmt(fmt) "xen:" KBUILD_MODNAME ": " fmt
  52
  53 #include <linux/atomic.h>
  54 #include <linux/module.h>
  55 #include <linux/miscdevice.h>
  56 #include <linux/kernel.h>
  57 #include <linux/init.h>
  58 #include <linux/slab.h>
  59 #include <linux/fs.h>
  60 #include <linux/device.h>
  61 #include <linux/mm.h>
  62 #include <linux/uaccess.h>
  63 #include <linux/types.h>
  64 #include <linux/list.h>
  65 #include <linux/highmem.h>
  66
  67 #include <xen/xen.h>
  68 #include <xen/page.h>
  69 #include <xen/grant_table.h>
  70 #include <xen/gntalloc.h>
  71 #include <xen/events.h>
  72
  73 static int limit = 1024;
  74 module_param(limit, int, 0644);
  75 MODULE_PARM_DESC(limit, "Maximum number of grants that may be allocated by "
  76                 "the gntalloc device");
  77
  78 static LIST_HEAD(gref_list);
  79 static DEFINE_MUTEX(gref_mutex);
  80 static int gref_size;
  81
  82 struct notify_info {
  83         uint16_t pgoff:12;    /* Bits 0-11: Offset of the byte to clear */
  84         uint16_t flags:2;     /* Bits 12-13: Unmap notification flags */
  85         int event;            /* Port (event channel) to notify */
  86 };
  87
  88 /* Metadata on a grant reference. */
  89 struct gntalloc_gref {
  90         struct list_head next_gref;  /* list entry gref_list */
  91         struct list_head next_file;  /* list entry file->list, if open */
  92         struct page *page;           /* The shared page */
  93         uint64_t file_index;         /* File offset for mmap() */
  94         unsigned int users;          /* Use count - when zero, waiting on Xen */
  95         grant_ref_t gref_id;         /* The grant reference number */
  96         struct notify_info notify;   /* Unmap notification */
  97 };
  98
  99 struct gntalloc_file_private_data {
 100         struct list_head list;
 101         uint64_t index;
 102 };
 103
 104 struct gntalloc_vma_private_data {
 105         struct gntalloc_gref *gref;
 106         int users;
 107         int count;
 108 };
 109
 110 static void __del_gref(struct gntalloc_gref *gref);
 111
 112 static void do_cleanup(void)
 113 {
 114         struct gntalloc_gref *gref, *n;
 115         list_for_each_entry_safe(gref, n, &gref_list, next_gref) {
 116                 if (!gref->users)
 117                         __del_gref(gref);
 118         }
 119 }
 120
 121 static int add_grefs(struct ioctl_gntalloc_alloc_gref *op,
 122         uint32_t *gref_ids, struct gntalloc_file_private_data *priv)
 123 {
 124         int i, rc, readonly;
 125         LIST_HEAD(queue_gref);
 126         LIST_HEAD(queue_file);
 127         struct gntalloc_gref *gref, *next;
 128
 129         readonly = !(op->flags & GNTALLOC_FLAG_WRITABLE);
 130         for (i = 0; i < op->count; i++) {
 131                 gref = kzalloc(sizeof(*gref), GFP_KERNEL);
 132                 if (!gref) {
 133                         rc = -ENOMEM;
 134                         goto undo;
 135                 }
 136                 list_add_tail(&gref->next_gref, &queue_gref);
 137                 list_add_tail(&gref->next_file, &queue_file);
 138                 gref->users = 1;
 139                 gref->file_index = op->index + i * PAGE_SIZE;
 140                 gref->page = alloc_page(GFP_KERNEL|__GFP_ZERO);
 141                 if (!gref->page) {
 142                         rc = -ENOMEM;
 143                         goto undo;
 144                 }
 145
 146                 /* Grant foreign access to the page. */
 147                 rc = gnttab_grant_foreign_access(op->domid,
 148                                                  xen_page_to_gfn(gref->page),
 149                                                  readonly);
 150                 if (rc < 0)
 151                         goto undo;
 152                 gref_ids[i] = gref->gref_id = rc;
 153         }
 154
 155         /* Add to gref lists. */
 156         mutex_lock(&gref_mutex);
 157         list_splice_tail(&queue_gref, &gref_list);
 158         list_splice_tail(&queue_file, &priv->list);
 159         mutex_unlock(&gref_mutex);
 160
 161         return 0;
 162
 163 undo:
 164         mutex_lock(&gref_mutex);
 165         gref_size -= (op->count - i);
 166
 167         list_for_each_entry_safe(gref, next, &queue_file, next_file) {
 168                 list_del(&gref->next_file);
 169                 __del_gref(gref);
 170         }
 171
 172         /* It's possible for the target domain to map the just-allocated grant
 173          * references by blindly guessing their IDs; if this is done, then
 174          * __del_gref will leave them in the queue_gref list. They need to be
 175          * added to the global list so that we can free them when they are no
 176          * longer referenced.
 177          */
 178         if (unlikely(!list_empty(&queue_gref)))
 179                 list_splice_tail(&queue_gref, &gref_list);
 180         mutex_unlock(&gref_mutex);
 181         return rc;
 182 }
 183
 184 static void __del_gref(struct gntalloc_gref *gref)
 185 {
 186         if (gref->notify.flags & UNMAP_NOTIFY_CLEAR_BYTE) {
 187                 uint8_t *tmp = kmap(gref->page);
 188                 tmp[gref->notify.pgoff] = 0;
 189                 kunmap(gref->page);
 190         }
 191         if (gref->notify.flags & UNMAP_NOTIFY_SEND_EVENT) {
 192                 notify_remote_via_evtchn(gref->notify.event);
 193                 evtchn_put(gref->notify.event);
 194         }
 195
 196         gref->notify.flags = 0;
 197
 198         if (gref->gref_id) {
 199                 if (gnttab_query_foreign_access(gref->gref_id))
 200                         return;
 201
 202                 if (!gnttab_end_foreign_access_ref(gref->gref_id, 0))
 203                         return;
 204
 205                 gnttab_free_grant_reference(gref->gref_id);
 206         }
 207
 208         gref_size--;
 209         list_del(&gref->next_gref);
 210
 211         if (gref->page)
 212                 __free_page(gref->page);
 213
 214         kfree(gref);
 215 }
 216
 217 /* finds contiguous grant references in a file, returns the first */
 218 static struct gntalloc_gref *find_grefs(struct gntalloc_file_private_data *priv,
 219                 uint64_t index, uint32_t count)
 220 {
 221         struct gntalloc_gref *rv = NULL, *gref;
 222         list_for_each_entry(gref, &priv->list, next_file) {
 223                 if (gref->file_index == index && !rv)
 224                         rv = gref;
 225                 if (rv) {
 226                         if (gref->file_index != index)
 227                                 return NULL;
 228                         index += PAGE_SIZE;
 229                         count--;
 230                         if (count == 0)
 231                                 return rv;
 232                 }
 233         }
 234         return NULL;
 235 }
 236
 237 /*
 238  * -------------------------------------
 239  *  File operations.
 240  * -------------------------------------
 241  */
 242 static int gntalloc_open(struct inode *inode, struct file *filp)
 243 {
 244         struct gntalloc_file_private_data *priv;
 245
 246         priv = kzalloc(sizeof(*priv), GFP_KERNEL);
 247         if (!priv)
 248                 goto out_nomem;
 249         INIT_LIST_HEAD(&priv->list);
 250
 251         filp->private_data = priv;
 252
 253         pr_debug("%s: priv %p\n", __func__, priv);
 254
 255         return 0;
 256
 257 out_nomem:
 258         return -ENOMEM;
 259 }
 260
 261 static int gntalloc_release(struct inode *inode, struct file *filp)
 262 {
 263         struct gntalloc_file_private_data *priv = filp->private_data;
 264         struct gntalloc_gref *gref;
 265
 266         pr_debug("%s: priv %p\n", __func__, priv);
 267
 268         mutex_lock(&gref_mutex);
 269         while (!list_empty(&priv->list)) {
 270                 gref = list_entry(priv->list.next,
 271                         struct gntalloc_gref, next_file);
 272                 list_del(&gref->next_file);
 273                 gref->users--;
 274                 if (gref->users == 0)
 275                         __del_gref(gref);
 276         }
 277         kfree(priv);
 278         mutex_unlock(&gref_mutex);
 279
 280         return 0;
 281 }
 282
 283 static long gntalloc_ioctl_alloc(struct gntalloc_file_private_data *priv,
 284                 struct ioctl_gntalloc_alloc_gref __user *arg)
 285 {
 286         int rc = 0;
 287         struct ioctl_gntalloc_alloc_gref op;
 288         uint32_t *gref_ids;
 289
 290         pr_debug("%s: priv %p\n", __func__, priv);
 291
 292         if (copy_from_user(&op, arg, sizeof(op))) {
 293                 rc = -EFAULT;
 294                 goto out;
 295         }
 296
 297         gref_ids = kcalloc(op.count, sizeof(gref_ids[0]), GFP_KERNEL);
 298         if (!gref_ids) {
 299                 rc = -ENOMEM;
 300                 goto out;
 301         }
 302
 303         mutex_lock(&gref_mutex);
 304         /* Clean up pages that were at zero (local) users but were still mapped
 305          * by remote domains. Since those pages count towards the limit that we
 306          * are about to enforce, removing them here is a good idea.
 307          */
 308         do_cleanup();
 309         if (gref_size + op.count > limit) {
 310                 mutex_unlock(&gref_mutex);
 311                 rc = -ENOSPC;
 312                 goto out_free;
 313         }
 314         gref_size += op.count;
 315         op.index = priv->index;
 316         priv->index += op.count * PAGE_SIZE;
 317         mutex_unlock(&gref_mutex);
 318
 319         rc = add_grefs(&op, gref_ids, priv);
 320         if (rc < 0)
 321                 goto out_free;
 322
 323         /* Once we finish add_grefs, it is unsafe to touch the new reference,
 324          * since it is possible for a concurrent ioctl to remove it (by guessing
 325          * its index). If the userspace application doesn't provide valid memory
 326          * to write the IDs to, then it will need to close the file in order to
 327          * release - which it will do by segfaulting when it tries to access the
 328          * IDs to close them.
 329          */
 330         if (copy_to_user(arg, &op, sizeof(op))) {
 331                 rc = -EFAULT;
 332                 goto out_free;
 333         }
 334         if (copy_to_user(arg->gref_ids, gref_ids,
 335                         sizeof(gref_ids[0]) * op.count)) {
 336                 rc = -EFAULT;
 337                 goto out_free;
 338         }
 339
 340 out_free:
 341         kfree(gref_ids);
 342 out:
 343         return rc;
 344 }
 345
 346 static long gntalloc_ioctl_dealloc(struct gntalloc_file_private_data *priv,
 347                 void __user *arg)
 348 {
 349         int i, rc = 0;
 350         struct ioctl_gntalloc_dealloc_gref op;
 351         struct gntalloc_gref *gref, *n;
 352
 353         pr_debug("%s: priv %p\n", __func__, priv);
 354
 355         if (copy_from_user(&op, arg, sizeof(op))) {
 356                 rc = -EFAULT;
 357                 goto dealloc_grant_out;
 358         }
 359
 360         mutex_lock(&gref_mutex);
 361         gref = find_grefs(priv, op.index, op.count);
 362         if (gref) {
 363                 /* Remove from the file list only, and decrease reference count.
 364                  * The later call to do_cleanup() will remove from gref_list and
 365                  * free the memory if the pages aren't mapped anywhere.
 366                  */
 367                 for (i = 0; i < op.count; i++) {
 368                         n = list_entry(gref->next_file.next,
 369                                 struct gntalloc_gref, next_file);
 370                         list_del(&gref->next_file);
 371                         gref->users--;
 372                         gref = n;
 373                 }
 374         } else {
 375                 rc = -EINVAL;
 376         }
 377
 378         do_cleanup();
 379
 380         mutex_unlock(&gref_mutex);
 381 dealloc_grant_out:
 382         return rc;
 383 }
 384
 385 static long gntalloc_ioctl_unmap_notify(struct gntalloc_file_private_data *priv,
 386                 void __user *arg)
 387 {
 388         struct ioctl_gntalloc_unmap_notify op;
 389         struct gntalloc_gref *gref;
 390         uint64_t index;
 391         int pgoff;
 392         int rc;
 393
 394         if (copy_from_user(&op, arg, sizeof(op)))
 395                 return -EFAULT;
 396
 397         index = op.index & ~(PAGE_SIZE - 1);
 398         pgoff = op.index & (PAGE_SIZE - 1);
 399
 400         mutex_lock(&gref_mutex);
 401
 402         gref = find_grefs(priv, index, 1);
 403         if (!gref) {
 404                 rc = -ENOENT;
 405                 goto unlock_out;
 406         }
 407
 408         if (op.action & ~(UNMAP_NOTIFY_CLEAR_BYTE|UNMAP_NOTIFY_SEND_EVENT)) {
 409                 rc = -EINVAL;
 410                 goto unlock_out;
 411         }
 412
 413         /* We need to grab a reference to the event channel we are going to use
 414          * to send the notify before releasing the reference we may already have
 415          * (if someone has called this ioctl twice). This is required so that
 416          * it is possible to change the clear_byte part of the notification
 417          * without disturbing the event channel part, which may now be the last
 418          * reference to that event channel.
 419          */
 420         if (op.action & UNMAP_NOTIFY_SEND_EVENT) {
 421                 if (evtchn_get(op.event_channel_port)) {
 422                         rc = -EINVAL;
 423                         goto unlock_out;
 424                 }
 425         }
 426
 427         if (gref->notify.flags & UNMAP_NOTIFY_SEND_EVENT)
 428                 evtchn_put(gref->notify.event);
 429
 430         gref->notify.flags = op.action;
 431         gref->notify.pgoff = pgoff;
 432         gref->notify.event = op.event_channel_port;
 433         rc = 0;
 434
 435  unlock_out:
 436         mutex_unlock(&gref_mutex);
 437         return rc;
 438 }
 439
 440 static long gntalloc_ioctl(struct file *filp, unsigned int cmd,
 441                 unsigned long arg)
 442 {
 443         struct gntalloc_file_private_data *priv = filp->private_data;
 444
 445         switch (cmd) {
 446         case IOCTL_GNTALLOC_ALLOC_GREF:
 447                 return gntalloc_ioctl_alloc(priv, (void __user *)arg);
 448
 449         case IOCTL_GNTALLOC_DEALLOC_GREF:
 450                 return gntalloc_ioctl_dealloc(priv, (void __user *)arg);
 451
 452         case IOCTL_GNTALLOC_SET_UNMAP_NOTIFY:
 453                 return gntalloc_ioctl_unmap_notify(priv, (void __user *)arg);
 454
 455         default:
 456                 return -ENOIOCTLCMD;
 457         }
 458
 459         return 0;
 460 }
 461
 462 static void gntalloc_vma_open(struct vm_area_struct *vma)
 463 {
 464         struct gntalloc_vma_private_data *priv = vma->vm_private_data;
 465
 466         if (!priv)
 467                 return;
 468
 469         mutex_lock(&gref_mutex);
 470         priv->users++;
 471         mutex_unlock(&gref_mutex);
 472 }
 473
 474 static void gntalloc_vma_close(struct vm_area_struct *vma)
 475 {
 476         struct gntalloc_vma_private_data *priv = vma->vm_private_data;
 477         struct gntalloc_gref *gref, *next;
 478         int i;
 479
 480         if (!priv)
 481                 return;
 482
 483         mutex_lock(&gref_mutex);
 484         priv->users--;
 485         if (priv->users == 0) {
 486                 gref = priv->gref;
 487                 for (i = 0; i < priv->count; i++) {
 488                         gref->users--;
 489                         next = list_entry(gref->next_gref.next,
 490                                           struct gntalloc_gref, next_gref);
 491                         if (gref->users == 0)
 492                                 __del_gref(gref);
 493                         gref = next;
 494                 }
 495                 kfree(priv);
 496         }
 497         mutex_unlock(&gref_mutex);
 498 }
 499
 500 static const struct vm_operations_struct gntalloc_vmops = {
 501         .open = gntalloc_vma_open,
 502         .close = gntalloc_vma_close,
 503 };
 504
 505 static int gntalloc_mmap(struct file *filp, struct vm_area_struct *vma)
 506 {
 507         struct gntalloc_file_private_data *priv = filp->private_data;
 508         struct gntalloc_vma_private_data *vm_priv;
 509         struct gntalloc_gref *gref;
 510         int count = vma_pages(vma);
 511         int rv, i;
 512
 513         if (!(vma->vm_flags & VM_SHARED)) {
 514                 pr_err("%s: Mapping must be shared\n", __func__);
 515                 return -EINVAL;
 516         }
 517
 518         vm_priv = kmalloc(sizeof(*vm_priv), GFP_KERNEL);
 519         if (!vm_priv)
 520                 return -ENOMEM;
 521
 522         mutex_lock(&gref_mutex);
 523
 524         pr_debug("%s: priv %p,%p, page %lu+%d\n", __func__,
 525                        priv, vm_priv, vma->vm_pgoff, count);
 526
 527         gref = find_grefs(priv, vma->vm_pgoff << PAGE_SHIFT, count);
 528         if (gref == NULL) {
 529                 rv = -ENOENT;
 530                 pr_debug("%s: Could not find grant reference",
 531                                 __func__);
 532                 kfree(vm_priv);
 533                 goto out_unlock;
 534         }
 535
 536         vm_priv->gref = gref;
 537         vm_priv->users = 1;
 538         vm_priv->count = count;
 539
 540         vma->vm_private_data = vm_priv;
 541
 542         vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP;
 543
 544         vma->vm_ops = &gntalloc_vmops;
 545
 546         for (i = 0; i < count; i++) {
 547                 gref->users++;
 548                 rv = vm_insert_page(vma, vma->vm_start + i * PAGE_SIZE,
 549                                 gref->page);
 550                 if (rv)
 551                         goto out_unlock;
 552
 553                 gref = list_entry(gref->next_file.next,
 554                                 struct gntalloc_gref, next_file);
 555         }
 556         rv = 0;
 557
 558 out_unlock:
 559         mutex_unlock(&gref_mutex);
 560         return rv;
 561 }
 562
 563 static const struct file_operations gntalloc_fops = {
 564         .owner = THIS_MODULE,
 565         .open = gntalloc_open,
 566         .release = gntalloc_release,
 567         .unlocked_ioctl = gntalloc_ioctl,
 568         .mmap = gntalloc_mmap
 569 };
 570
 571 /*
 572  * -------------------------------------
 573  * Module creation/destruction.
 574  * -------------------------------------
 575  */
 576 static struct miscdevice gntalloc_miscdev = {
 577         .minor  = MISC_DYNAMIC_MINOR,
 578         .name   = "xen/gntalloc",
 579         .fops   = &gntalloc_fops,
 580 };
 581
 582 static int __init gntalloc_init(void)
 583 {
 584         int err;
 585
 586         if (!xen_domain())
 587                 return -ENODEV;
 588
 589         err = misc_register(&gntalloc_miscdev);
 590         if (err != 0) {
 591                 pr_err("Could not register misc gntalloc device\n");
 592                 return err;
 593         }
 594
 595         pr_debug("Created grant allocation device at %d,%d\n",
 596                         MISC_MAJOR, gntalloc_miscdev.minor);
 597
 598         return 0;
 599 }
 600
 601 static void __exit gntalloc_exit(void)
 602 {
 603         misc_deregister(&gntalloc_miscdev);
 604 }
 605
 606 module_init(gntalloc_init);
 607 module_exit(gntalloc_exit);
 608
 609 MODULE_LICENSE("GPL");
 610 MODULE_AUTHOR("Carter Weatherly <carter.weatherly@jhuapl.edu>, "
 611                 "Daniel De Graaf <dgdegra@tycho.nsa.gov>");
 612 MODULE_DESCRIPTION("User-space grant reference allocator driver");