LXR linux/drivers/xen/xenbus/xenbus_dev

   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