1 // SPDX-License-Identifier: GPL-2.0
2 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
3 
4 #include <linux/slab.h>
5 #include <linux/types.h>
6 #include <linux/mm.h>
7 #include <linux/fs.h>
8 #include <linux/miscdevice.h>
9 #include <linux/init.h>
10 #include <linux/capability.h>
11 
12 #include <xen/xen.h>
13 #include <xen/page.h>
14 #include <xen/xenbus.h>
15 #include <xen/xenbus_dev.h>
16 #include <xen/grant_table.h>
17 #include <xen/events.h>
18 #include <asm/xen/hypervisor.h>
19 
20 #include "xenbus.h"
21 
22 static int xenbus_backend_open(struct inode *inode, struct file *filp)
23 {
24 	if (!capable(CAP_SYS_ADMIN))
25 		return -EPERM;
26 
27 	return nonseekable_open(inode, filp);
28 }
29 
30 static long xenbus_alloc(domid_t domid)
31 {
32 	struct evtchn_alloc_unbound arg;
33 	int err = -EEXIST;
34 
35 	xs_suspend();
36 
37 	/* If xenstored_ready is nonzero, that means we have already talked to
38 	 * xenstore and set up watches. These watches will be restored by
39 	 * xs_resume, but that requires communication over the port established
40 	 * below that is not visible to anyone until the ioctl returns.
41 	 *
42 	 * This can be resolved by splitting the ioctl into two parts
43 	 * (postponing the resume until xenstored is active) but this is
44 	 * unnecessarily complex for the intended use where xenstored is only
45 	 * started once - so return -EEXIST if it's already running.
46 	 */
47 	if (xenstored_ready)
48 		goto out_err;
49 
50 	gnttab_grant_foreign_access_ref(GNTTAB_RESERVED_XENSTORE, domid,
51 			virt_to_gfn(xen_store_interface), 0 /* writable */);
52 
53 	arg.dom = DOMID_SELF;
54 	arg.remote_dom = domid;
55 
56 	err = HYPERVISOR_event_channel_op(EVTCHNOP_alloc_unbound, &arg);
57 	if (err)
58 		goto out_err;
59 
60 	if (xen_store_evtchn > 0)
61 		xb_deinit_comms();
62 
63 	xen_store_evtchn = arg.port;
64 
65 	xs_resume();
66 
67 	return arg.port;
68 
69  out_err:
70 	xs_suspend_cancel();
71 	return err;
72 }
73 
74 static long xenbus_backend_ioctl(struct file *file, unsigned int cmd,
75 				 unsigned long data)
76 {
77 	if (!capable(CAP_SYS_ADMIN))
78 		return -EPERM;
79 
80 	switch (cmd) {
81 	case IOCTL_XENBUS_BACKEND_EVTCHN:
82 		if (xen_store_evtchn > 0)
83 			return xen_store_evtchn;
84 		return -ENODEV;
85 	case IOCTL_XENBUS_BACKEND_SETUP:
86 		return xenbus_alloc(data);
87 	default:
88 		return -ENOTTY;
89 	}
90 }
91 
92 static int xenbus_backend_mmap(struct file *file, struct vm_area_struct *vma)
93 {
94 	size_t size = vma->vm_end - vma->vm_start;
95 
96 	if (!capable(CAP_SYS_ADMIN))
97 		return -EPERM;
98 
99 	if ((size > PAGE_SIZE) || (vma->vm_pgoff != 0))
100 		return -EINVAL;
101 
102 	if (remap_pfn_range(vma, vma->vm_start,
103 			    virt_to_pfn(xen_store_interface),
104 			    size, vma->vm_page_prot))
105 		return -EAGAIN;
106 
107 	return 0;
108 }
109 
110 static const struct file_operations xenbus_backend_fops = {
111 	.open = xenbus_backend_open,
112 	.mmap = xenbus_backend_mmap,
113 	.unlocked_ioctl = xenbus_backend_ioctl,
114 };
115 
116 static struct miscdevice xenbus_backend_dev = {
117 	.minor = MISC_DYNAMIC_MINOR,
118 	.name = "xen/xenbus_backend",
119 	.fops = &xenbus_backend_fops,
120 };
121 
122 static int __init xenbus_backend_init(void)
123 {
124 	int err;
125 
126 	if (!xen_initial_domain())
127 		return -ENODEV;
128 
129 	err = misc_register(&xenbus_backend_dev);
130 	if (err)
131 		pr_err("Could not register xenbus backend device\n");
132 	return err;
133 }
134 device_initcall(xenbus_backend_init);
135