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
73static int limit = 1024;
74module_param(limit, int, 0644);
75MODULE_PARM_DESC(limit, "Maximum number of grants that may be allocated by "
76		"the gntalloc device");
77
78static LIST_HEAD(gref_list);
79static DEFINE_MUTEX(gref_mutex);
80static int gref_size;
81
82struct 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. */
89struct 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
99struct gntalloc_file_private_data {
100	struct list_head list;
101	uint64_t index;
102};
103
104struct gntalloc_vma_private_data {
105	struct gntalloc_gref *gref;
106	int users;
107	int count;
108};
109
110static void __del_gref(struct gntalloc_gref *gref);
111
112static 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
121static 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	rc = -ENOMEM;
131	for (i = 0; i < op->count; i++) {
132		gref = kzalloc(sizeof(*gref), GFP_KERNEL);
133		if (!gref)
134			goto undo;
135		list_add_tail(&gref->next_gref, &queue_gref);
136		list_add_tail(&gref->next_file, &queue_file);
137		gref->users = 1;
138		gref->file_index = op->index + i * PAGE_SIZE;
139		gref->page = alloc_page(GFP_KERNEL|__GFP_ZERO);
140		if (!gref->page)
141			goto undo;
142
143		/* Grant foreign access to the page. */
144		rc = gnttab_grant_foreign_access(op->domid,
145			pfn_to_mfn(page_to_pfn(gref->page)), readonly);
146		if (rc < 0)
147			goto undo;
148		gref_ids[i] = gref->gref_id = rc;
149	}
150
151	/* Add to gref lists. */
152	mutex_lock(&gref_mutex);
153	list_splice_tail(&queue_gref, &gref_list);
154	list_splice_tail(&queue_file, &priv->list);
155	mutex_unlock(&gref_mutex);
156
157	return 0;
158
159undo:
160	mutex_lock(&gref_mutex);
161	gref_size -= (op->count - i);
162
163	list_for_each_entry_safe(gref, next, &queue_file, next_file) {
164		list_del(&gref->next_file);
165		__del_gref(gref);
166	}
167
168	/* It's possible for the target domain to map the just-allocated grant
169	 * references by blindly guessing their IDs; if this is done, then
170	 * __del_gref will leave them in the queue_gref list. They need to be
171	 * added to the global list so that we can free them when they are no
172	 * longer referenced.
173	 */
174	if (unlikely(!list_empty(&queue_gref)))
175		list_splice_tail(&queue_gref, &gref_list);
176	mutex_unlock(&gref_mutex);
177	return rc;
178}
179
180static void __del_gref(struct gntalloc_gref *gref)
181{
182	if (gref->notify.flags & UNMAP_NOTIFY_CLEAR_BYTE) {
183		uint8_t *tmp = kmap(gref->page);
184		tmp[gref->notify.pgoff] = 0;
185		kunmap(gref->page);
186	}
187	if (gref->notify.flags & UNMAP_NOTIFY_SEND_EVENT) {
188		notify_remote_via_evtchn(gref->notify.event);
189		evtchn_put(gref->notify.event);
190	}
191
192	gref->notify.flags = 0;
193
194	if (gref->gref_id) {
195		if (gnttab_query_foreign_access(gref->gref_id))
196			return;
197
198		if (!gnttab_end_foreign_access_ref(gref->gref_id, 0))
199			return;
200
201		gnttab_free_grant_reference(gref->gref_id);
202	}
203
204	gref_size--;
205	list_del(&gref->next_gref);
206
207	if (gref->page)
208		__free_page(gref->page);
209
210	kfree(gref);
211}
212
213/* finds contiguous grant references in a file, returns the first */
214static struct gntalloc_gref *find_grefs(struct gntalloc_file_private_data *priv,
215		uint64_t index, uint32_t count)
216{
217	struct gntalloc_gref *rv = NULL, *gref;
218	list_for_each_entry(gref, &priv->list, next_file) {
219		if (gref->file_index == index && !rv)
220			rv = gref;
221		if (rv) {
222			if (gref->file_index != index)
223				return NULL;
224			index += PAGE_SIZE;
225			count--;
226			if (count == 0)
227				return rv;
228		}
229	}
230	return NULL;
231}
232
233/*
234 * -------------------------------------
235 *  File operations.
236 * -------------------------------------
237 */
238static int gntalloc_open(struct inode *inode, struct file *filp)
239{
240	struct gntalloc_file_private_data *priv;
241
242	priv = kzalloc(sizeof(*priv), GFP_KERNEL);
243	if (!priv)
244		goto out_nomem;
245	INIT_LIST_HEAD(&priv->list);
246
247	filp->private_data = priv;
248
249	pr_debug("%s: priv %p\n", __func__, priv);
250
251	return 0;
252
253out_nomem:
254	return -ENOMEM;
255}
256
257static int gntalloc_release(struct inode *inode, struct file *filp)
258{
259	struct gntalloc_file_private_data *priv = filp->private_data;
260	struct gntalloc_gref *gref;
261
262	pr_debug("%s: priv %p\n", __func__, priv);
263
264	mutex_lock(&gref_mutex);
265	while (!list_empty(&priv->list)) {
266		gref = list_entry(priv->list.next,
267			struct gntalloc_gref, next_file);
268		list_del(&gref->next_file);
269		gref->users--;
270		if (gref->users == 0)
271			__del_gref(gref);
272	}
273	kfree(priv);
274	mutex_unlock(&gref_mutex);
275
276	return 0;
277}
278
279static long gntalloc_ioctl_alloc(struct gntalloc_file_private_data *priv,
280		struct ioctl_gntalloc_alloc_gref __user *arg)
281{
282	int rc = 0;
283	struct ioctl_gntalloc_alloc_gref op;
284	uint32_t *gref_ids;
285
286	pr_debug("%s: priv %p\n", __func__, priv);
287
288	if (copy_from_user(&op, arg, sizeof(op))) {
289		rc = -EFAULT;
290		goto out;
291	}
292
293	gref_ids = kcalloc(op.count, sizeof(gref_ids[0]), GFP_TEMPORARY);
294	if (!gref_ids) {
295		rc = -ENOMEM;
296		goto out;
297	}
298
299	mutex_lock(&gref_mutex);
300	/* Clean up pages that were at zero (local) users but were still mapped
301	 * by remote domains. Since those pages count towards the limit that we
302	 * are about to enforce, removing them here is a good idea.
303	 */
304	do_cleanup();
305	if (gref_size + op.count > limit) {
306		mutex_unlock(&gref_mutex);
307		rc = -ENOSPC;
308		goto out_free;
309	}
310	gref_size += op.count;
311	op.index = priv->index;
312	priv->index += op.count * PAGE_SIZE;
313	mutex_unlock(&gref_mutex);
314
315	rc = add_grefs(&op, gref_ids, priv);
316	if (rc < 0)
317		goto out_free;
318
319	/* Once we finish add_grefs, it is unsafe to touch the new reference,
320	 * since it is possible for a concurrent ioctl to remove it (by guessing
321	 * its index). If the userspace application doesn't provide valid memory
322	 * to write the IDs to, then it will need to close the file in order to
323	 * release - which it will do by segfaulting when it tries to access the
324	 * IDs to close them.
325	 */
326	if (copy_to_user(arg, &op, sizeof(op))) {
327		rc = -EFAULT;
328		goto out_free;
329	}
330	if (copy_to_user(arg->gref_ids, gref_ids,
331			sizeof(gref_ids[0]) * op.count)) {
332		rc = -EFAULT;
333		goto out_free;
334	}
335
336out_free:
337	kfree(gref_ids);
338out:
339	return rc;
340}
341
342static long gntalloc_ioctl_dealloc(struct gntalloc_file_private_data *priv,
343		void __user *arg)
344{
345	int i, rc = 0;
346	struct ioctl_gntalloc_dealloc_gref op;
347	struct gntalloc_gref *gref, *n;
348
349	pr_debug("%s: priv %p\n", __func__, priv);
350
351	if (copy_from_user(&op, arg, sizeof(op))) {
352		rc = -EFAULT;
353		goto dealloc_grant_out;
354	}
355
356	mutex_lock(&gref_mutex);
357	gref = find_grefs(priv, op.index, op.count);
358	if (gref) {
359		/* Remove from the file list only, and decrease reference count.
360		 * The later call to do_cleanup() will remove from gref_list and
361		 * free the memory if the pages aren't mapped anywhere.
362		 */
363		for (i = 0; i < op.count; i++) {
364			n = list_entry(gref->next_file.next,
365				struct gntalloc_gref, next_file);
366			list_del(&gref->next_file);
367			gref->users--;
368			gref = n;
369		}
370	} else {
371		rc = -EINVAL;
372	}
373
374	do_cleanup();
375
376	mutex_unlock(&gref_mutex);
377dealloc_grant_out:
378	return rc;
379}
380
381static long gntalloc_ioctl_unmap_notify(struct gntalloc_file_private_data *priv,
382		void __user *arg)
383{
384	struct ioctl_gntalloc_unmap_notify op;
385	struct gntalloc_gref *gref;
386	uint64_t index;
387	int pgoff;
388	int rc;
389
390	if (copy_from_user(&op, arg, sizeof(op)))
391		return -EFAULT;
392
393	index = op.index & ~(PAGE_SIZE - 1);
394	pgoff = op.index & (PAGE_SIZE - 1);
395
396	mutex_lock(&gref_mutex);
397
398	gref = find_grefs(priv, index, 1);
399	if (!gref) {
400		rc = -ENOENT;
401		goto unlock_out;
402	}
403
404	if (op.action & ~(UNMAP_NOTIFY_CLEAR_BYTE|UNMAP_NOTIFY_SEND_EVENT)) {
405		rc = -EINVAL;
406		goto unlock_out;
407	}
408
409	/* We need to grab a reference to the event channel we are going to use
410	 * to send the notify before releasing the reference we may already have
411	 * (if someone has called this ioctl twice). This is required so that
412	 * it is possible to change the clear_byte part of the notification
413	 * without disturbing the event channel part, which may now be the last
414	 * reference to that event channel.
415	 */
416	if (op.action & UNMAP_NOTIFY_SEND_EVENT) {
417		if (evtchn_get(op.event_channel_port)) {
418			rc = -EINVAL;
419			goto unlock_out;
420		}
421	}
422
423	if (gref->notify.flags & UNMAP_NOTIFY_SEND_EVENT)
424		evtchn_put(gref->notify.event);
425
426	gref->notify.flags = op.action;
427	gref->notify.pgoff = pgoff;
428	gref->notify.event = op.event_channel_port;
429	rc = 0;
430
431 unlock_out:
432	mutex_unlock(&gref_mutex);
433	return rc;
434}
435
436static long gntalloc_ioctl(struct file *filp, unsigned int cmd,
437		unsigned long arg)
438{
439	struct gntalloc_file_private_data *priv = filp->private_data;
440
441	switch (cmd) {
442	case IOCTL_GNTALLOC_ALLOC_GREF:
443		return gntalloc_ioctl_alloc(priv, (void __user *)arg);
444
445	case IOCTL_GNTALLOC_DEALLOC_GREF:
446		return gntalloc_ioctl_dealloc(priv, (void __user *)arg);
447
448	case IOCTL_GNTALLOC_SET_UNMAP_NOTIFY:
449		return gntalloc_ioctl_unmap_notify(priv, (void __user *)arg);
450
451	default:
452		return -ENOIOCTLCMD;
453	}
454
455	return 0;
456}
457
458static void gntalloc_vma_open(struct vm_area_struct *vma)
459{
460	struct gntalloc_vma_private_data *priv = vma->vm_private_data;
461
462	if (!priv)
463		return;
464
465	mutex_lock(&gref_mutex);
466	priv->users++;
467	mutex_unlock(&gref_mutex);
468}
469
470static void gntalloc_vma_close(struct vm_area_struct *vma)
471{
472	struct gntalloc_vma_private_data *priv = vma->vm_private_data;
473	struct gntalloc_gref *gref, *next;
474	int i;
475
476	if (!priv)
477		return;
478
479	mutex_lock(&gref_mutex);
480	priv->users--;
481	if (priv->users == 0) {
482		gref = priv->gref;
483		for (i = 0; i < priv->count; i++) {
484			gref->users--;
485			next = list_entry(gref->next_gref.next,
486					  struct gntalloc_gref, next_gref);
487			if (gref->users == 0)
488				__del_gref(gref);
489			gref = next;
490		}
491		kfree(priv);
492	}
493	mutex_unlock(&gref_mutex);
494}
495
496static struct vm_operations_struct gntalloc_vmops = {
497	.open = gntalloc_vma_open,
498	.close = gntalloc_vma_close,
499};
500
501static int gntalloc_mmap(struct file *filp, struct vm_area_struct *vma)
502{
503	struct gntalloc_file_private_data *priv = filp->private_data;
504	struct gntalloc_vma_private_data *vm_priv;
505	struct gntalloc_gref *gref;
506	int count = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
507	int rv, i;
508
509	if (!(vma->vm_flags & VM_SHARED)) {
510		pr_err("%s: Mapping must be shared\n", __func__);
511		return -EINVAL;
512	}
513
514	vm_priv = kmalloc(sizeof(*vm_priv), GFP_KERNEL);
515	if (!vm_priv)
516		return -ENOMEM;
517
518	mutex_lock(&gref_mutex);
519
520	pr_debug("%s: priv %p,%p, page %lu+%d\n", __func__,
521		       priv, vm_priv, vma->vm_pgoff, count);
522
523	gref = find_grefs(priv, vma->vm_pgoff << PAGE_SHIFT, count);
524	if (gref == NULL) {
525		rv = -ENOENT;
526		pr_debug("%s: Could not find grant reference",
527				__func__);
528		kfree(vm_priv);
529		goto out_unlock;
530	}
531
532	vm_priv->gref = gref;
533	vm_priv->users = 1;
534	vm_priv->count = count;
535
536	vma->vm_private_data = vm_priv;
537
538	vma->vm_flags |= VM_DONTEXPAND | VM_DONTDUMP;
539
540	vma->vm_ops = &gntalloc_vmops;
541
542	for (i = 0; i < count; i++) {
543		gref->users++;
544		rv = vm_insert_page(vma, vma->vm_start + i * PAGE_SIZE,
545				gref->page);
546		if (rv)
547			goto out_unlock;
548
549		gref = list_entry(gref->next_file.next,
550				struct gntalloc_gref, next_file);
551	}
552	rv = 0;
553
554out_unlock:
555	mutex_unlock(&gref_mutex);
556	return rv;
557}
558
559static const struct file_operations gntalloc_fops = {
560	.owner = THIS_MODULE,
561	.open = gntalloc_open,
562	.release = gntalloc_release,
563	.unlocked_ioctl = gntalloc_ioctl,
564	.mmap = gntalloc_mmap
565};
566
567/*
568 * -------------------------------------
569 * Module creation/destruction.
570 * -------------------------------------
571 */
572static struct miscdevice gntalloc_miscdev = {
573	.minor	= MISC_DYNAMIC_MINOR,
574	.name	= "xen/gntalloc",
575	.fops	= &gntalloc_fops,
576};
577
578static int __init gntalloc_init(void)
579{
580	int err;
581
582	if (!xen_domain())
583		return -ENODEV;
584
585	err = misc_register(&gntalloc_miscdev);
586	if (err != 0) {
587		pr_err("Could not register misc gntalloc device\n");
588		return err;
589	}
590
591	pr_debug("Created grant allocation device at %d,%d\n",
592			MISC_MAJOR, gntalloc_miscdev.minor);
593
594	return 0;
595}
596
597static void __exit gntalloc_exit(void)
598{
599	misc_deregister(&gntalloc_miscdev);
600}
601
602module_init(gntalloc_init);
603module_exit(gntalloc_exit);
604
605MODULE_LICENSE("GPL");
606MODULE_AUTHOR("Carter Weatherly <carter.weatherly@jhuapl.edu>, "
607		"Daniel De Graaf <dgdegra@tycho.nsa.gov>");
608MODULE_DESCRIPTION("User-space grant reference allocator driver");
609