drivers/xen/xenbus/xenbus_dev_backend.c

   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);