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
22static 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
30static 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
74static 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
92static 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
110static 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
116static struct miscdevice xenbus_backend_dev = {
117	.minor = MISC_DYNAMIC_MINOR,
118	.name = "xen/xenbus_backend",
119	.fops = &xenbus_backend_fops,
120};
121
122static 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}
134device_initcall(xenbus_backend_init);
135