xref: /openbmc/linux/drivers/xen/gntalloc.c (revision 1c71222e)
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 
do_cleanup(void)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 
add_grefs(struct ioctl_gntalloc_alloc_gref * op,uint32_t * gref_ids,struct gntalloc_file_private_data * priv)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 	mutex_unlock(&gref_mutex);
173 	return rc;
174 }
175 
__del_gref(struct gntalloc_gref * gref)176 static void __del_gref(struct gntalloc_gref *gref)
177 {
178 	if (gref->notify.flags & UNMAP_NOTIFY_CLEAR_BYTE) {
179 		uint8_t *tmp = kmap_local_page(gref->page);
180 		tmp[gref->notify.pgoff] = 0;
181 		kunmap_local(tmp);
182 	}
183 	if (gref->notify.flags & UNMAP_NOTIFY_SEND_EVENT) {
184 		notify_remote_via_evtchn(gref->notify.event);
185 		evtchn_put(gref->notify.event);
186 	}
187 
188 	gref->notify.flags = 0;
189 
190 	if (gref->gref_id) {
191 		if (gref->page)
192 			gnttab_end_foreign_access(gref->gref_id, gref->page);
193 		else
194 			gnttab_free_grant_reference(gref->gref_id);
195 	}
196 
197 	gref_size--;
198 	list_del(&gref->next_gref);
199 
200 	kfree(gref);
201 }
202 
203 /* finds contiguous grant references in a file, returns the first */
find_grefs(struct gntalloc_file_private_data * priv,uint64_t index,uint32_t count)204 static struct gntalloc_gref *find_grefs(struct gntalloc_file_private_data *priv,
205 		uint64_t index, uint32_t count)
206 {
207 	struct gntalloc_gref *rv = NULL, *gref;
208 	list_for_each_entry(gref, &priv->list, next_file) {
209 		if (gref->file_index == index && !rv)
210 			rv = gref;
211 		if (rv) {
212 			if (gref->file_index != index)
213 				return NULL;
214 			index += PAGE_SIZE;
215 			count--;
216 			if (count == 0)
217 				return rv;
218 		}
219 	}
220 	return NULL;
221 }
222 
223 /*
224  * -------------------------------------
225  *  File operations.
226  * -------------------------------------
227  */
gntalloc_open(struct inode * inode,struct file * filp)228 static int gntalloc_open(struct inode *inode, struct file *filp)
229 {
230 	struct gntalloc_file_private_data *priv;
231 
232 	priv = kzalloc(sizeof(*priv), GFP_KERNEL);
233 	if (!priv)
234 		goto out_nomem;
235 	INIT_LIST_HEAD(&priv->list);
236 
237 	filp->private_data = priv;
238 
239 	pr_debug("%s: priv %p\n", __func__, priv);
240 
241 	return 0;
242 
243 out_nomem:
244 	return -ENOMEM;
245 }
246 
gntalloc_release(struct inode * inode,struct file * filp)247 static int gntalloc_release(struct inode *inode, struct file *filp)
248 {
249 	struct gntalloc_file_private_data *priv = filp->private_data;
250 	struct gntalloc_gref *gref;
251 
252 	pr_debug("%s: priv %p\n", __func__, priv);
253 
254 	mutex_lock(&gref_mutex);
255 	while (!list_empty(&priv->list)) {
256 		gref = list_entry(priv->list.next,
257 			struct gntalloc_gref, next_file);
258 		list_del(&gref->next_file);
259 		gref->users--;
260 		if (gref->users == 0)
261 			__del_gref(gref);
262 	}
263 	kfree(priv);
264 	mutex_unlock(&gref_mutex);
265 
266 	return 0;
267 }
268 
gntalloc_ioctl_alloc(struct gntalloc_file_private_data * priv,struct ioctl_gntalloc_alloc_gref __user * arg)269 static long gntalloc_ioctl_alloc(struct gntalloc_file_private_data *priv,
270 		struct ioctl_gntalloc_alloc_gref __user *arg)
271 {
272 	int rc = 0;
273 	struct ioctl_gntalloc_alloc_gref op;
274 	uint32_t *gref_ids;
275 
276 	pr_debug("%s: priv %p\n", __func__, priv);
277 
278 	if (copy_from_user(&op, arg, sizeof(op))) {
279 		rc = -EFAULT;
280 		goto out;
281 	}
282 
283 	gref_ids = kcalloc(op.count, sizeof(gref_ids[0]), GFP_KERNEL);
284 	if (!gref_ids) {
285 		rc = -ENOMEM;
286 		goto out;
287 	}
288 
289 	mutex_lock(&gref_mutex);
290 	/* Clean up pages that were at zero (local) users but were still mapped
291 	 * by remote domains. Since those pages count towards the limit that we
292 	 * are about to enforce, removing them here is a good idea.
293 	 */
294 	do_cleanup();
295 	if (gref_size + op.count > limit) {
296 		mutex_unlock(&gref_mutex);
297 		rc = -ENOSPC;
298 		goto out_free;
299 	}
300 	gref_size += op.count;
301 	op.index = priv->index;
302 	priv->index += op.count * PAGE_SIZE;
303 	mutex_unlock(&gref_mutex);
304 
305 	rc = add_grefs(&op, gref_ids, priv);
306 	if (rc < 0)
307 		goto out_free;
308 
309 	/* Once we finish add_grefs, it is unsafe to touch the new reference,
310 	 * since it is possible for a concurrent ioctl to remove it (by guessing
311 	 * its index). If the userspace application doesn't provide valid memory
312 	 * to write the IDs to, then it will need to close the file in order to
313 	 * release - which it will do by segfaulting when it tries to access the
314 	 * IDs to close them.
315 	 */
316 	if (copy_to_user(arg, &op, sizeof(op))) {
317 		rc = -EFAULT;
318 		goto out_free;
319 	}
320 	if (copy_to_user(arg->gref_ids, gref_ids,
321 			sizeof(gref_ids[0]) * op.count)) {
322 		rc = -EFAULT;
323 		goto out_free;
324 	}
325 
326 out_free:
327 	kfree(gref_ids);
328 out:
329 	return rc;
330 }
331 
gntalloc_ioctl_dealloc(struct gntalloc_file_private_data * priv,void __user * arg)332 static long gntalloc_ioctl_dealloc(struct gntalloc_file_private_data *priv,
333 		void __user *arg)
334 {
335 	int i, rc = 0;
336 	struct ioctl_gntalloc_dealloc_gref op;
337 	struct gntalloc_gref *gref, *n;
338 
339 	pr_debug("%s: priv %p\n", __func__, priv);
340 
341 	if (copy_from_user(&op, arg, sizeof(op))) {
342 		rc = -EFAULT;
343 		goto dealloc_grant_out;
344 	}
345 
346 	mutex_lock(&gref_mutex);
347 	gref = find_grefs(priv, op.index, op.count);
348 	if (gref) {
349 		/* Remove from the file list only, and decrease reference count.
350 		 * The later call to do_cleanup() will remove from gref_list and
351 		 * free the memory if the pages aren't mapped anywhere.
352 		 */
353 		for (i = 0; i < op.count; i++) {
354 			n = list_entry(gref->next_file.next,
355 				struct gntalloc_gref, next_file);
356 			list_del(&gref->next_file);
357 			gref->users--;
358 			gref = n;
359 		}
360 	} else {
361 		rc = -EINVAL;
362 	}
363 
364 	do_cleanup();
365 
366 	mutex_unlock(&gref_mutex);
367 dealloc_grant_out:
368 	return rc;
369 }
370 
gntalloc_ioctl_unmap_notify(struct gntalloc_file_private_data * priv,void __user * arg)371 static long gntalloc_ioctl_unmap_notify(struct gntalloc_file_private_data *priv,
372 		void __user *arg)
373 {
374 	struct ioctl_gntalloc_unmap_notify op;
375 	struct gntalloc_gref *gref;
376 	uint64_t index;
377 	int pgoff;
378 	int rc;
379 
380 	if (copy_from_user(&op, arg, sizeof(op)))
381 		return -EFAULT;
382 
383 	index = op.index & ~(PAGE_SIZE - 1);
384 	pgoff = op.index & (PAGE_SIZE - 1);
385 
386 	mutex_lock(&gref_mutex);
387 
388 	gref = find_grefs(priv, index, 1);
389 	if (!gref) {
390 		rc = -ENOENT;
391 		goto unlock_out;
392 	}
393 
394 	if (op.action & ~(UNMAP_NOTIFY_CLEAR_BYTE|UNMAP_NOTIFY_SEND_EVENT)) {
395 		rc = -EINVAL;
396 		goto unlock_out;
397 	}
398 
399 	/* We need to grab a reference to the event channel we are going to use
400 	 * to send the notify before releasing the reference we may already have
401 	 * (if someone has called this ioctl twice). This is required so that
402 	 * it is possible to change the clear_byte part of the notification
403 	 * without disturbing the event channel part, which may now be the last
404 	 * reference to that event channel.
405 	 */
406 	if (op.action & UNMAP_NOTIFY_SEND_EVENT) {
407 		if (evtchn_get(op.event_channel_port)) {
408 			rc = -EINVAL;
409 			goto unlock_out;
410 		}
411 	}
412 
413 	if (gref->notify.flags & UNMAP_NOTIFY_SEND_EVENT)
414 		evtchn_put(gref->notify.event);
415 
416 	gref->notify.flags = op.action;
417 	gref->notify.pgoff = pgoff;
418 	gref->notify.event = op.event_channel_port;
419 	rc = 0;
420 
421  unlock_out:
422 	mutex_unlock(&gref_mutex);
423 	return rc;
424 }
425 
gntalloc_ioctl(struct file * filp,unsigned int cmd,unsigned long arg)426 static long gntalloc_ioctl(struct file *filp, unsigned int cmd,
427 		unsigned long arg)
428 {
429 	struct gntalloc_file_private_data *priv = filp->private_data;
430 
431 	switch (cmd) {
432 	case IOCTL_GNTALLOC_ALLOC_GREF:
433 		return gntalloc_ioctl_alloc(priv, (void __user *)arg);
434 
435 	case IOCTL_GNTALLOC_DEALLOC_GREF:
436 		return gntalloc_ioctl_dealloc(priv, (void __user *)arg);
437 
438 	case IOCTL_GNTALLOC_SET_UNMAP_NOTIFY:
439 		return gntalloc_ioctl_unmap_notify(priv, (void __user *)arg);
440 
441 	default:
442 		return -ENOIOCTLCMD;
443 	}
444 
445 	return 0;
446 }
447 
gntalloc_vma_open(struct vm_area_struct * vma)448 static void gntalloc_vma_open(struct vm_area_struct *vma)
449 {
450 	struct gntalloc_vma_private_data *priv = vma->vm_private_data;
451 
452 	if (!priv)
453 		return;
454 
455 	mutex_lock(&gref_mutex);
456 	priv->users++;
457 	mutex_unlock(&gref_mutex);
458 }
459 
gntalloc_vma_close(struct vm_area_struct * vma)460 static void gntalloc_vma_close(struct vm_area_struct *vma)
461 {
462 	struct gntalloc_vma_private_data *priv = vma->vm_private_data;
463 	struct gntalloc_gref *gref, *next;
464 	int i;
465 
466 	if (!priv)
467 		return;
468 
469 	mutex_lock(&gref_mutex);
470 	priv->users--;
471 	if (priv->users == 0) {
472 		gref = priv->gref;
473 		for (i = 0; i < priv->count; i++) {
474 			gref->users--;
475 			next = list_entry(gref->next_gref.next,
476 					  struct gntalloc_gref, next_gref);
477 			if (gref->users == 0)
478 				__del_gref(gref);
479 			gref = next;
480 		}
481 		kfree(priv);
482 	}
483 	mutex_unlock(&gref_mutex);
484 }
485 
486 static const struct vm_operations_struct gntalloc_vmops = {
487 	.open = gntalloc_vma_open,
488 	.close = gntalloc_vma_close,
489 };
490 
gntalloc_mmap(struct file * filp,struct vm_area_struct * vma)491 static int gntalloc_mmap(struct file *filp, struct vm_area_struct *vma)
492 {
493 	struct gntalloc_file_private_data *priv = filp->private_data;
494 	struct gntalloc_vma_private_data *vm_priv;
495 	struct gntalloc_gref *gref;
496 	int count = vma_pages(vma);
497 	int rv, i;
498 
499 	if (!(vma->vm_flags & VM_SHARED)) {
500 		pr_err("%s: Mapping must be shared\n", __func__);
501 		return -EINVAL;
502 	}
503 
504 	vm_priv = kmalloc(sizeof(*vm_priv), GFP_KERNEL);
505 	if (!vm_priv)
506 		return -ENOMEM;
507 
508 	mutex_lock(&gref_mutex);
509 
510 	pr_debug("%s: priv %p,%p, page %lu+%d\n", __func__,
511 		       priv, vm_priv, vma->vm_pgoff, count);
512 
513 	gref = find_grefs(priv, vma->vm_pgoff << PAGE_SHIFT, count);
514 	if (gref == NULL) {
515 		rv = -ENOENT;
516 		pr_debug("%s: Could not find grant reference",
517 				__func__);
518 		kfree(vm_priv);
519 		goto out_unlock;
520 	}
521 
522 	vm_priv->gref = gref;
523 	vm_priv->users = 1;
524 	vm_priv->count = count;
525 
526 	vma->vm_private_data = vm_priv;
527 
528 	vm_flags_set(vma, VM_DONTEXPAND | VM_DONTDUMP);
529 
530 	vma->vm_ops = &gntalloc_vmops;
531 
532 	for (i = 0; i < count; i++) {
533 		gref->users++;
534 		rv = vm_insert_page(vma, vma->vm_start + i * PAGE_SIZE,
535 				gref->page);
536 		if (rv)
537 			goto out_unlock;
538 
539 		gref = list_entry(gref->next_file.next,
540 				struct gntalloc_gref, next_file);
541 	}
542 	rv = 0;
543 
544 out_unlock:
545 	mutex_unlock(&gref_mutex);
546 	return rv;
547 }
548 
549 static const struct file_operations gntalloc_fops = {
550 	.owner = THIS_MODULE,
551 	.open = gntalloc_open,
552 	.release = gntalloc_release,
553 	.unlocked_ioctl = gntalloc_ioctl,
554 	.mmap = gntalloc_mmap
555 };
556 
557 /*
558  * -------------------------------------
559  * Module creation/destruction.
560  * -------------------------------------
561  */
562 static struct miscdevice gntalloc_miscdev = {
563 	.minor	= MISC_DYNAMIC_MINOR,
564 	.name	= "xen/gntalloc",
565 	.fops	= &gntalloc_fops,
566 };
567 
gntalloc_init(void)568 static int __init gntalloc_init(void)
569 {
570 	int err;
571 
572 	if (!xen_domain())
573 		return -ENODEV;
574 
575 	err = misc_register(&gntalloc_miscdev);
576 	if (err != 0) {
577 		pr_err("Could not register misc gntalloc device\n");
578 		return err;
579 	}
580 
581 	pr_debug("Created grant allocation device at %d,%d\n",
582 			MISC_MAJOR, gntalloc_miscdev.minor);
583 
584 	return 0;
585 }
586 
gntalloc_exit(void)587 static void __exit gntalloc_exit(void)
588 {
589 	misc_deregister(&gntalloc_miscdev);
590 }
591 
592 module_init(gntalloc_init);
593 module_exit(gntalloc_exit);
594 
595 MODULE_LICENSE("GPL");
596 MODULE_AUTHOR("Carter Weatherly <carter.weatherly@jhuapl.edu>, "
597 		"Daniel De Graaf <dgdegra@tycho.nsa.gov>");
598 MODULE_DESCRIPTION("User-space grant reference allocator driver");
599