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); 135