xen/xenbus/xenbus_dev_backend.c

0001 // SPDX-License-Identifier: GPL-2.0
0002 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
0003
0004 #include <linux/slab.h>
0005 #include <linux/types.h>
0006 #include <linux/mm.h>
0007 #include <linux/fs.h>
0008 #include <linux/miscdevice.h>
0009 #include <linux/init.h>
0010 #include <linux/capability.h>
0011
0012 #include <xen/xen.h>
0013 #include <xen/page.h>
0014 #include <xen/xenbus.h>
0015 #include <xen/xenbus_dev.h>
0016 #include <xen/grant_table.h>
0017 #include <xen/events.h>
0018 #include <asm/xen/hypervisor.h>
0019
0020 #include "xenbus.h"
0021
0022 static int xenbus_backend_open(struct inode *inode, struct file *filp)
0023 {
0024     if (!capable(CAP_SYS_ADMIN))
0025         return -EPERM;
0026
0027     return nonseekable_open(inode, filp);
0028 }
0029
0030 static long xenbus_alloc(domid_t domid)
0031 {
0032     struct evtchn_alloc_unbound arg;
0033     int err = -EEXIST;
0034
0035     xs_suspend();
0036
0037     /* If xenstored_ready is nonzero, that means we have already talked to
0038      * xenstore and set up watches. These watches will be restored by
0039      * xs_resume, but that requires communication over the port established
0040      * below that is not visible to anyone until the ioctl returns.
0041      *
0042      * This can be resolved by splitting the ioctl into two parts
0043      * (postponing the resume until xenstored is active) but this is
0044      * unnecessarily complex for the intended use where xenstored is only
0045      * started once - so return -EEXIST if it's already running.
0046      */
0047     if (xenstored_ready)
0048         goto out_err;
0049
0050     gnttab_grant_foreign_access_ref(GNTTAB_RESERVED_XENSTORE, domid,
0051             virt_to_gfn(xen_store_interface), 0 /* writable */);
0052
0053     arg.dom = DOMID_SELF;
0054     arg.remote_dom = domid;
0055
0056     err = HYPERVISOR_event_channel_op(EVTCHNOP_alloc_unbound, &arg);
0057     if (err)
0058         goto out_err;
0059
0060     if (xen_store_evtchn > 0)
0061         xb_deinit_comms();
0062
0063     xen_store_evtchn = arg.port;
0064
0065     xs_resume();
0066
0067     return arg.port;
0068
0069  out_err:
0070     xs_suspend_cancel();
0071     return err;
0072 }
0073
0074 static long xenbus_backend_ioctl(struct file *file, unsigned int cmd,
0075                  unsigned long data)
0076 {
0077     if (!capable(CAP_SYS_ADMIN))
0078         return -EPERM;
0079
0080     switch (cmd) {
0081     case IOCTL_XENBUS_BACKEND_EVTCHN:
0082         if (xen_store_evtchn > 0)
0083             return xen_store_evtchn;
0084         return -ENODEV;
0085     case IOCTL_XENBUS_BACKEND_SETUP:
0086         return xenbus_alloc(data);
0087     default:
0088         return -ENOTTY;
0089     }
0090 }
0091
0092 static int xenbus_backend_mmap(struct file *file, struct vm_area_struct *vma)
0093 {
0094     size_t size = vma->vm_end - vma->vm_start;
0095
0096     if (!capable(CAP_SYS_ADMIN))
0097         return -EPERM;
0098
0099     if ((size > PAGE_SIZE) || (vma->vm_pgoff != 0))
0100         return -EINVAL;
0101
0102     if (remap_pfn_range(vma, vma->vm_start,
0103                 virt_to_pfn(xen_store_interface),
0104                 size, vma->vm_page_prot))
0105         return -EAGAIN;
0106
0107     return 0;
0108 }
0109
0110 static const struct file_operations xenbus_backend_fops = {
0111     .open = xenbus_backend_open,
0112     .mmap = xenbus_backend_mmap,
0113     .unlocked_ioctl = xenbus_backend_ioctl,
0114 };
0115
0116 static struct miscdevice xenbus_backend_dev = {
0117     .minor = MISC_DYNAMIC_MINOR,
0118     .name = "xen/xenbus_backend",
0119     .fops = &xenbus_backend_fops,
0120 };
0121
0122 static int __init xenbus_backend_init(void)
0123 {
0124     int err;
0125
0126     if (!xen_initial_domain())
0127         return -ENODEV;
0128
0129     err = misc_register(&xenbus_backend_dev);
0130     if (err)
0131         pr_err("Could not register xenbus backend device\n");
0132     return err;
0133 }
0134 device_initcall(xenbus_backend_init);