1 #include <linux/slab.h>
2 #include <linux/types.h>
3 #include <linux/mm.h>
4 #include <linux/fs.h>
5 #include <linux/miscdevice.h>
6 #include <linux/module.h>
7 #include <linux/capability.h>
8 
9 #include <xen/xen.h>
10 #include <xen/page.h>
11 #include <xen/xenbus.h>
12 #include <xen/xenbus_dev.h>
13 #include <xen/grant_table.h>
14 #include <xen/events.h>
15 #include <asm/xen/hypervisor.h>
16 
17 #include "xenbus_comms.h"
18 
19 MODULE_LICENSE("GPL");
20 
21 static int xenbus_backend_open(struct inode *inode, struct file *filp)
22 {
23 	if (!capable(CAP_SYS_ADMIN))
24 		return -EPERM;
25 
26 	return nonseekable_open(inode, filp);
27 }
28 
29 static long xenbus_alloc(domid_t domid)
30 {
31 	struct evtchn_alloc_unbound arg;
32 	int err = -EEXIST;
33 
34 	xs_suspend();
35 
36 	/* If xenstored_ready is nonzero, that means we have already talked to
37 	 * xenstore and set up watches. These watches will be restored by
38 	 * xs_resume, but that requires communication over the port established
39 	 * below that is not visible to anyone until the ioctl returns.
40 	 *
41 	 * This can be resolved by splitting the ioctl into two parts
42 	 * (postponing the resume until xenstored is active) but this is
43 	 * unnecessarily complex for the intended use where xenstored is only
44 	 * started once - so return -EEXIST if it's already running.
45 	 */
46 	if (xenstored_ready)
47 		goto out_err;
48 
49 	gnttab_grant_foreign_access_ref(GNTTAB_RESERVED_XENSTORE, domid,
50 			virt_to_mfn(xen_store_interface), 0 /* writable */);
51 
52 	arg.dom = DOMID_SELF;
53 	arg.remote_dom = domid;
54 
55 	err = HYPERVISOR_event_channel_op(EVTCHNOP_alloc_unbound, &arg);
56 	if (err)
57 		goto out_err;
58 
59 	if (xen_store_evtchn > 0)
60 		xb_deinit_comms();
61 
62 	xen_store_evtchn = arg.port;
63 
64 	xs_resume();
65 
66 	return arg.port;
67 
68  out_err:
69 	xs_suspend_cancel();
70 	return err;
71 }
72 
73 static long xenbus_backend_ioctl(struct file *file, unsigned int cmd,
74 				 unsigned long data)
75 {
76 	if (!capable(CAP_SYS_ADMIN))
77 		return -EPERM;
78 
79 	switch (cmd) {
80 	case IOCTL_XENBUS_BACKEND_EVTCHN:
81 		if (xen_store_evtchn > 0)
82 			return xen_store_evtchn;
83 		return -ENODEV;
84 	case IOCTL_XENBUS_BACKEND_SETUP:
85 		return xenbus_alloc(data);
86 	default:
87 		return -ENOTTY;
88 	}
89 }
90 
91 static int xenbus_backend_mmap(struct file *file, struct vm_area_struct *vma)
92 {
93 	size_t size = vma->vm_end - vma->vm_start;
94 
95 	if (!capable(CAP_SYS_ADMIN))
96 		return -EPERM;
97 
98 	if ((size > PAGE_SIZE) || (vma->vm_pgoff != 0))
99 		return -EINVAL;
100 
101 	if (remap_pfn_range(vma, vma->vm_start,
102 			    virt_to_pfn(xen_store_interface),
103 			    size, vma->vm_page_prot))
104 		return -EAGAIN;
105 
106 	return 0;
107 }
108 
109 static const struct file_operations xenbus_backend_fops = {
110 	.open = xenbus_backend_open,
111 	.mmap = xenbus_backend_mmap,
112 	.unlocked_ioctl = xenbus_backend_ioctl,
113 };
114 
115 static struct miscdevice xenbus_backend_dev = {
116 	.minor = MISC_DYNAMIC_MINOR,
117 	.name = "xen/xenbus_backend",
118 	.fops = &xenbus_backend_fops,
119 };
120 
121 static int __init xenbus_backend_init(void)
122 {
123 	int err;
124 
125 	if (!xen_initial_domain())
126 		return -ENODEV;
127 
128 	err = misc_register(&xenbus_backend_dev);
129 	if (err)
130 		printk(KERN_ERR "Could not register xenbus backend device\n");
131 	return err;
132 }
133 
134 static void __exit xenbus_backend_exit(void)
135 {
136 	misc_deregister(&xenbus_backend_dev);
137 }
138 
139 module_init(xenbus_backend_init);
140 module_exit(xenbus_backend_exit);
141