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);