1 /*- 2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD 3 * 4 * Copyright (c) 1999 Assar Westerlund 5 * All rights reserved. 6 * 7 * Redistribution and use in source and binary forms, with or without 8 * modification, are permitted provided that the following conditions 9 * are met: 10 * 1. Redistributions of source code must retain the above copyright 11 * notice, this list of conditions and the following disclaimer. 12 * 2. Redistributions in binary form must reproduce the above copyright 13 * notice, this list of conditions and the following disclaimer in the 14 * documentation and/or other materials provided with the distribution. 15 * 16 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND 17 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE 18 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE 19 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE 20 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL 21 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS 22 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) 23 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT 24 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY 25 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF 26 * SUCH DAMAGE. 27 */ 28 29 #include <sys/cdefs.h> 30 __FBSDID("$FreeBSD$"); 31 32 #include <sys/param.h> 33 #include <sys/kernel.h> 34 #include <sys/lock.h> 35 #include <sys/module.h> 36 #include <sys/mutex.h> 37 #include <sys/proc.h> 38 #include <sys/resourcevar.h> 39 #include <sys/sx.h> 40 #include <sys/syscall.h> 41 #include <sys/sysent.h> 42 #include <sys/sysproto.h> 43 #include <sys/systm.h> 44 #include <machine/atomic.h> 45 46 /* 47 * Acts like "nosys" but can be identified in sysent for dynamic call 48 * number assignment for a limited number of calls. 49 * 50 * Place holder for system call slots reserved for loadable modules. 51 */ 52 int 53 lkmnosys(struct thread *td, struct nosys_args *args) 54 { 55 56 return (nosys(td, args)); 57 } 58 59 int 60 lkmressys(struct thread *td, struct nosys_args *args) 61 { 62 63 return (nosys(td, args)); 64 } 65 66 static void 67 syscall_thread_drain(struct sysent *se) 68 { 69 u_int32_t cnt, oldcnt; 70 71 do { 72 oldcnt = se->sy_thrcnt; 73 KASSERT((oldcnt & SY_THR_STATIC) == 0, 74 ("drain on static syscall")); 75 cnt = oldcnt | SY_THR_DRAINING; 76 } while (atomic_cmpset_acq_32(&se->sy_thrcnt, oldcnt, cnt) == 0); 77 while (atomic_cmpset_32(&se->sy_thrcnt, SY_THR_DRAINING, 78 SY_THR_ABSENT) == 0) 79 pause("scdrn", hz/2); 80 } 81 82 int 83 syscall_thread_enter(struct thread *td, struct sysent *se) 84 { 85 u_int32_t cnt, oldcnt; 86 87 do { 88 oldcnt = se->sy_thrcnt; 89 if ((oldcnt & SY_THR_STATIC) != 0) 90 return (0); 91 if ((oldcnt & (SY_THR_DRAINING | SY_THR_ABSENT)) != 0) 92 return (ENOSYS); 93 cnt = oldcnt + SY_THR_INCR; 94 } while (atomic_cmpset_acq_32(&se->sy_thrcnt, oldcnt, cnt) == 0); 95 return (0); 96 } 97 98 void 99 syscall_thread_exit(struct thread *td, struct sysent *se) 100 { 101 u_int32_t cnt, oldcnt; 102 103 do { 104 oldcnt = se->sy_thrcnt; 105 if ((oldcnt & SY_THR_STATIC) != 0) 106 return; 107 cnt = oldcnt - SY_THR_INCR; 108 } while (atomic_cmpset_rel_32(&se->sy_thrcnt, oldcnt, cnt) == 0); 109 } 110 111 int 112 syscall_register(int *offset, struct sysent *new_sysent, 113 struct sysent *old_sysent, int flags) 114 { 115 int i; 116 117 if ((flags & ~SY_THR_STATIC) != 0) 118 return (EINVAL); 119 120 if (*offset == NO_SYSCALL) { 121 for (i = 1; i < SYS_MAXSYSCALL; ++i) 122 if (sysent[i].sy_call == (sy_call_t *)lkmnosys) 123 break; 124 if (i == SYS_MAXSYSCALL) 125 return (ENFILE); 126 *offset = i; 127 } else if (*offset < 0 || *offset >= SYS_MAXSYSCALL) 128 return (EINVAL); 129 else if (sysent[*offset].sy_call != (sy_call_t *)lkmnosys && 130 sysent[*offset].sy_call != (sy_call_t *)lkmressys) 131 return (EEXIST); 132 133 KASSERT(sysent[*offset].sy_thrcnt == SY_THR_ABSENT, 134 ("dynamic syscall is not protected")); 135 *old_sysent = sysent[*offset]; 136 new_sysent->sy_thrcnt = SY_THR_ABSENT; 137 sysent[*offset] = *new_sysent; 138 atomic_store_rel_32(&sysent[*offset].sy_thrcnt, flags); 139 return (0); 140 } 141 142 int 143 syscall_deregister(int *offset, struct sysent *old_sysent) 144 { 145 struct sysent *se; 146 147 if (*offset == 0) 148 return (0); /* XXX? */ 149 150 se = &sysent[*offset]; 151 if ((se->sy_thrcnt & SY_THR_STATIC) != 0) 152 return (EINVAL); 153 syscall_thread_drain(se); 154 sysent[*offset] = *old_sysent; 155 return (0); 156 } 157 158 int 159 syscall_module_handler(struct module *mod, int what, void *arg) 160 { 161 struct syscall_module_data *data = arg; 162 modspecific_t ms; 163 int error; 164 165 switch (what) { 166 case MOD_LOAD: 167 error = syscall_register(data->offset, data->new_sysent, 168 &data->old_sysent, data->flags); 169 if (error) { 170 /* Leave a mark so we know to safely unload below. */ 171 data->offset = NULL; 172 return (error); 173 } 174 ms.intval = *data->offset; 175 MOD_XLOCK; 176 module_setspecific(mod, &ms); 177 MOD_XUNLOCK; 178 if (data->chainevh) 179 error = data->chainevh(mod, what, data->chainarg); 180 return (error); 181 case MOD_UNLOAD: 182 /* 183 * MOD_LOAD failed, so just return without calling the 184 * chained handler since we didn't pass along the MOD_LOAD 185 * event. 186 */ 187 if (data->offset == NULL) 188 return (0); 189 if (data->chainevh) { 190 error = data->chainevh(mod, what, data->chainarg); 191 if (error) 192 return error; 193 } 194 error = syscall_deregister(data->offset, &data->old_sysent); 195 return (error); 196 default: 197 if (data->chainevh) 198 return (data->chainevh(mod, what, data->chainarg)); 199 return (EOPNOTSUPP); 200 } 201 202 /* NOTREACHED */ 203 } 204 205 int 206 syscall_helper_register(struct syscall_helper_data *sd, int flags) 207 { 208 struct syscall_helper_data *sd1; 209 int error; 210 211 for (sd1 = sd; sd1->syscall_no != NO_SYSCALL; sd1++) { 212 error = syscall_register(&sd1->syscall_no, &sd1->new_sysent, 213 &sd1->old_sysent, flags); 214 if (error != 0) { 215 syscall_helper_unregister(sd); 216 return (error); 217 } 218 sd1->registered = 1; 219 } 220 return (0); 221 } 222 223 int 224 syscall_helper_unregister(struct syscall_helper_data *sd) 225 { 226 struct syscall_helper_data *sd1; 227 228 for (sd1 = sd; sd1->registered != 0; sd1++) { 229 syscall_deregister(&sd1->syscall_no, &sd1->old_sysent); 230 sd1->registered = 0; 231 } 232 return (0); 233 } 234