1 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt 2 3 #include <linux/slab.h> 4 #include <linux/types.h> 5 #include <linux/mm.h> 6 #include <linux/fs.h> 7 #include <linux/miscdevice.h> 8 #include <linux/init.h> 9 #include <linux/capability.h> 10 11 #include <xen/xen.h> 12 #include <xen/page.h> 13 #include <xen/xenbus.h> 14 #include <xen/xenbus_dev.h> 15 #include <xen/grant_table.h> 16 #include <xen/events.h> 17 #include <asm/xen/hypervisor.h> 18 19 #include "xenbus.h" 20 21 static int xenbus_backend_open(struct inode *inode, struct file *filp) 22 { 23 if (!capable(CAP_SYS_ADMIN)) 24 return -EPERM; 25 26 return nonseekable_open(inode, filp); 27 } 28 29 static long xenbus_alloc(domid_t domid) 30 { 31 struct evtchn_alloc_unbound arg; 32 int err = -EEXIST; 33 34 xs_suspend(); 35 36 /* If xenstored_ready is nonzero, that means we have already talked to 37 * xenstore and set up watches. These watches will be restored by 38 * xs_resume, but that requires communication over the port established 39 * below that is not visible to anyone until the ioctl returns. 40 * 41 * This can be resolved by splitting the ioctl into two parts 42 * (postponing the resume until xenstored is active) but this is 43 * unnecessarily complex for the intended use where xenstored is only 44 * started once - so return -EEXIST if it's already running. 45 */ 46 if (xenstored_ready) 47 goto out_err; 48 49 gnttab_grant_foreign_access_ref(GNTTAB_RESERVED_XENSTORE, domid, 50 virt_to_gfn(xen_store_interface), 0 /* writable */); 51 52 arg.dom = DOMID_SELF; 53 arg.remote_dom = domid; 54 55 err = HYPERVISOR_event_channel_op(EVTCHNOP_alloc_unbound, &arg); 56 if (err) 57 goto out_err; 58 59 if (xen_store_evtchn > 0) 60 xb_deinit_comms(); 61 62 xen_store_evtchn = arg.port; 63 64 xs_resume(); 65 66 return arg.port; 67 68 out_err: 69 xs_suspend_cancel(); 70 return err; 71 } 72 73 static long xenbus_backend_ioctl(struct file *file, unsigned int cmd, 74 unsigned long data) 75 { 76 if (!capable(CAP_SYS_ADMIN)) 77 return -EPERM; 78 79 switch (cmd) { 80 case IOCTL_XENBUS_BACKEND_EVTCHN: 81 if (xen_store_evtchn > 0) 82 return xen_store_evtchn; 83 return -ENODEV; 84 case IOCTL_XENBUS_BACKEND_SETUP: 85 return xenbus_alloc(data); 86 default: 87 return -ENOTTY; 88 } 89 } 90 91 static int xenbus_backend_mmap(struct file *file, struct vm_area_struct *vma) 92 { 93 size_t size = vma->vm_end - vma->vm_start; 94 95 if (!capable(CAP_SYS_ADMIN)) 96 return -EPERM; 97 98 if ((size > PAGE_SIZE) || (vma->vm_pgoff != 0)) 99 return -EINVAL; 100 101 if (remap_pfn_range(vma, vma->vm_start, 102 virt_to_pfn(xen_store_interface), 103 size, vma->vm_page_prot)) 104 return -EAGAIN; 105 106 return 0; 107 } 108 109 static const struct file_operations xenbus_backend_fops = { 110 .open = xenbus_backend_open, 111 .mmap = xenbus_backend_mmap, 112 .unlocked_ioctl = xenbus_backend_ioctl, 113 }; 114 115 static struct miscdevice xenbus_backend_dev = { 116 .minor = MISC_DYNAMIC_MINOR, 117 .name = "xen/xenbus_backend", 118 .fops = &xenbus_backend_fops, 119 }; 120 121 static int __init xenbus_backend_init(void) 122 { 123 int err; 124 125 if (!xen_initial_domain()) 126 return -ENODEV; 127 128 err = misc_register(&xenbus_backend_dev); 129 if (err) 130 pr_err("Could not register xenbus backend device\n"); 131 return err; 132 } 133 device_initcall(xenbus_backend_init); 134