1 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
2 
3 #include <linux/slab.h>
4 #include <linux/types.h>
5 #include <linux/mm.h>
6 #include <linux/fs.h>
7 #include <linux/miscdevice.h>
8 #include <linux/module.h>
9 #include <linux/capability.h>
10 
11 #include <xen/xen.h>
12 #include <xen/page.h>
13 #include <xen/xenbus.h>
14 #include <xen/xenbus_dev.h>
15 #include <xen/grant_table.h>
16 #include <xen/events.h>
17 #include <asm/xen/hypervisor.h>
18 
19 #include "xenbus_comms.h"
20 
21 MODULE_LICENSE("GPL");
22 
23 static int xenbus_backend_open(struct inode *inode, struct file *filp)
24 {
25 	if (!capable(CAP_SYS_ADMIN))
26 		return -EPERM;
27 
28 	return nonseekable_open(inode, filp);
29 }
30 
31 static long xenbus_alloc(domid_t domid)
32 {
33 	struct evtchn_alloc_unbound arg;
34 	int err = -EEXIST;
35 
36 	xs_suspend();
37 
38 	/* If xenstored_ready is nonzero, that means we have already talked to
39 	 * xenstore and set up watches. These watches will be restored by
40 	 * xs_resume, but that requires communication over the port established
41 	 * below that is not visible to anyone until the ioctl returns.
42 	 *
43 	 * This can be resolved by splitting the ioctl into two parts
44 	 * (postponing the resume until xenstored is active) but this is
45 	 * unnecessarily complex for the intended use where xenstored is only
46 	 * started once - so return -EEXIST if it's already running.
47 	 */
48 	if (xenstored_ready)
49 		goto out_err;
50 
51 	gnttab_grant_foreign_access_ref(GNTTAB_RESERVED_XENSTORE, domid,
52 			virt_to_gfn(xen_store_interface), 0 /* writable */);
53 
54 	arg.dom = DOMID_SELF;
55 	arg.remote_dom = domid;
56 
57 	err = HYPERVISOR_event_channel_op(EVTCHNOP_alloc_unbound, &arg);
58 	if (err)
59 		goto out_err;
60 
61 	if (xen_store_evtchn > 0)
62 		xb_deinit_comms();
63 
64 	xen_store_evtchn = arg.port;
65 
66 	xs_resume();
67 
68 	return arg.port;
69 
70  out_err:
71 	xs_suspend_cancel();
72 	return err;
73 }
74 
75 static long xenbus_backend_ioctl(struct file *file, unsigned int cmd,
76 				 unsigned long data)
77 {
78 	if (!capable(CAP_SYS_ADMIN))
79 		return -EPERM;
80 
81 	switch (cmd) {
82 	case IOCTL_XENBUS_BACKEND_EVTCHN:
83 		if (xen_store_evtchn > 0)
84 			return xen_store_evtchn;
85 		return -ENODEV;
86 	case IOCTL_XENBUS_BACKEND_SETUP:
87 		return xenbus_alloc(data);
88 	default:
89 		return -ENOTTY;
90 	}
91 }
92 
93 static int xenbus_backend_mmap(struct file *file, struct vm_area_struct *vma)
94 {
95 	size_t size = vma->vm_end - vma->vm_start;
96 
97 	if (!capable(CAP_SYS_ADMIN))
98 		return -EPERM;
99 
100 	if ((size > PAGE_SIZE) || (vma->vm_pgoff != 0))
101 		return -EINVAL;
102 
103 	if (remap_pfn_range(vma, vma->vm_start,
104 			    virt_to_pfn(xen_store_interface),
105 			    size, vma->vm_page_prot))
106 		return -EAGAIN;
107 
108 	return 0;
109 }
110 
111 static const struct file_operations xenbus_backend_fops = {
112 	.open = xenbus_backend_open,
113 	.mmap = xenbus_backend_mmap,
114 	.unlocked_ioctl = xenbus_backend_ioctl,
115 };
116 
117 static struct miscdevice xenbus_backend_dev = {
118 	.minor = MISC_DYNAMIC_MINOR,
119 	.name = "xen/xenbus_backend",
120 	.fops = &xenbus_backend_fops,
121 };
122 
123 static int __init xenbus_backend_init(void)
124 {
125 	int err;
126 
127 	if (!xen_initial_domain())
128 		return -ENODEV;
129 
130 	err = misc_register(&xenbus_backend_dev);
131 	if (err)
132 		pr_err("Could not register xenbus backend device\n");
133 	return err;
134 }
135 
136 static void __exit xenbus_backend_exit(void)
137 {
138 	misc_deregister(&xenbus_backend_dev);
139 }
140 
141 module_init(xenbus_backend_init);
142 module_exit(xenbus_backend_exit);
143