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1// SPDX-License-Identifier: GPL-2.02#define pr_fmt(fmt) KBUILD_MODNAME ": " fmt3 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 to38 * xenstore and set up watches. These watches will be restored by39 * xs_resume, but that requires communication over the port established40 * below that is not visible to anyone until the ioctl returns.41 *42 * This can be resolved by splitting the ioctl into two parts43 * (postponing the resume until xenstored is active) but this is44 * unnecessarily complex for the intended use where xenstored is only45 * 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