kern_syscalls.c

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    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         uint32_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         uint32_t cnt, oldcnt;
   86 
   87         KASSERT((se->sy_thrcnt & SY_THR_STATIC) == 0,
   88             ("%s: not a static syscall", __func__));
   89 
   90         do {
   91                 oldcnt = se->sy_thrcnt;
   92                 if ((oldcnt & (SY_THR_DRAINING | SY_THR_ABSENT)) != 0)
   93                         return (ENOSYS);
   94                 cnt = oldcnt + SY_THR_INCR;
   95         } while (atomic_cmpset_acq_32(&se->sy_thrcnt, oldcnt, cnt) == 0);
   96         return (0);
   97 }
   98 
   99 void
  100 syscall_thread_exit(struct thread *td, struct sysent *se)
  101 {
  102         uint32_t cnt, oldcnt;
  103 
  104         KASSERT((se->sy_thrcnt & SY_THR_STATIC) == 0,
  105             ("%s: not a static syscall", __func__));
  106 
  107         do {
  108                 oldcnt = se->sy_thrcnt;
  109                 cnt = oldcnt - SY_THR_INCR;
  110         } while (atomic_cmpset_rel_32(&se->sy_thrcnt, oldcnt, cnt) == 0);
  111 }
  112 
  113 int
  114 kern_syscall_register(struct sysent *sysents, int *offset,
  115     struct sysent *new_sysent, struct sysent *old_sysent, int flags)
  116 {
  117         int i;
  118 
  119         if ((flags & ~SY_THR_STATIC) != 0)
  120                 return (EINVAL);
  121 
  122         if (*offset == NO_SYSCALL) {
  123                 for (i = 1; i < SYS_MAXSYSCALL; ++i)
  124                         if (sysents[i].sy_call == (sy_call_t *)lkmnosys)
  125                                 break;
  126                 if (i == SYS_MAXSYSCALL)
  127                         return (ENFILE);
  128                 *offset = i;
  129         } else if (*offset < 0 || *offset >= SYS_MAXSYSCALL) {
  130                 return (EINVAL);
  131         } else if (sysents[*offset].sy_call != (sy_call_t *)lkmnosys &&
  132             sysents[*offset].sy_call != (sy_call_t *)lkmressys) {
  133                 KASSERT(sysents[*offset].sy_call != NULL,
  134                     ("undefined syscall %d", *offset));
  135                 return (EEXIST);
  136         }
  137 
  138         KASSERT(sysents[*offset].sy_thrcnt == SY_THR_ABSENT,
  139             ("dynamic syscall is not protected"));
  140         *old_sysent = sysents[*offset];
  141         new_sysent->sy_thrcnt = SY_THR_ABSENT;
  142         sysents[*offset] = *new_sysent;
  143         atomic_store_rel_32(&sysents[*offset].sy_thrcnt, flags);
  144         return (0);
  145 }
  146 
  147 int
  148 kern_syscall_deregister(struct sysent *sysents, int offset,
  149     const struct sysent *old_sysent)
  150 {
  151         struct sysent *se;
  152 
  153         if (offset == 0)
  154                 return (0); /* XXX? */
  155 
  156         se = &sysents[offset];
  157         if ((se->sy_thrcnt & SY_THR_STATIC) != 0)
  158                 return (EINVAL);
  159         syscall_thread_drain(se);
  160         sysents[offset] = *old_sysent;
  161         return (0);
  162 }
  163 
  164 int
  165 syscall_module_handler(struct module *mod, int what, void *arg)
  166 {
  167 
  168         return (kern_syscall_module_handler(sysent, mod, what, arg));
  169 }
  170 
  171 int
  172 kern_syscall_module_handler(struct sysent *sysents, struct module *mod,
  173     int what, void *arg)
  174 {
  175         struct syscall_module_data *data = arg;
  176         modspecific_t ms;
  177         int error;
  178 
  179         switch (what) {
  180         case MOD_LOAD:
  181                 error = kern_syscall_register(sysents, data->offset,
  182                     data->new_sysent, &data->old_sysent, data->flags);
  183                 if (error) {
  184                         /* Leave a mark so we know to safely unload below. */
  185                         data->offset = NULL;
  186                         return (error);
  187                 }
  188                 ms.intval = *data->offset;
  189                 MOD_XLOCK;
  190                 module_setspecific(mod, &ms);
  191                 MOD_XUNLOCK;
  192                 if (data->chainevh)
  193                         error = data->chainevh(mod, what, data->chainarg);
  194                 return (error);
  195         case MOD_UNLOAD:
  196                 /*
  197                  * MOD_LOAD failed, so just return without calling the
  198                  * chained handler since we didn't pass along the MOD_LOAD
  199                  * event.
  200                  */
  201                 if (data->offset == NULL)
  202                         return (0);
  203                 if (data->chainevh) {
  204                         error = data->chainevh(mod, what, data->chainarg);
  205                         if (error)
  206                                 return error;
  207                 }
  208                 error = kern_syscall_deregister(sysents, *data->offset,
  209                     &data->old_sysent);
  210                 return (error);
  211         default:
  212                 if (data->chainevh)
  213                         return (data->chainevh(mod, what, data->chainarg));
  214                 return (EOPNOTSUPP);
  215         }
  216 
  217         /* NOTREACHED */
  218 }
  219 
  220 int
  221 syscall_helper_register(struct syscall_helper_data *sd, int flags)
  222 {
  223 
  224         return (kern_syscall_helper_register(sysent, sd, flags));
  225 }
  226 
  227 int
  228 kern_syscall_helper_register(struct sysent *sysents,
  229     struct syscall_helper_data *sd, int flags)
  230 {
  231         struct syscall_helper_data *sd1;
  232         int error;
  233 
  234         for (sd1 = sd; sd1->syscall_no != NO_SYSCALL; sd1++) {
  235                 error = kern_syscall_register(sysents, &sd1->syscall_no,
  236                     &sd1->new_sysent, &sd1->old_sysent, flags);
  237                 if (error != 0) {
  238                         kern_syscall_helper_unregister(sysents, sd);
  239                         return (error);
  240                 }
  241                 sd1->registered = 1;
  242         }
  243         return (0);
  244 }
  245 
  246 int
  247 syscall_helper_unregister(struct syscall_helper_data *sd)
  248 {
  249 
  250         return (kern_syscall_helper_unregister(sysent, sd));
  251 }
  252 
  253 int
  254 kern_syscall_helper_unregister(struct sysent *sysents,
  255     struct syscall_helper_data *sd)
  256 {
  257         struct syscall_helper_data *sd1;
  258 
  259         for (sd1 = sd; sd1->registered != 0; sd1++) {
  260                 kern_syscall_deregister(sysents, sd1->syscall_no,
  261                     &sd1->old_sysent);
  262                 sd1->registered = 0;
  263         }
  264         return (0);
  265 }

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FreeBSD/Linux Kernel Cross Reference sys/kern/kern_syscalls.c

FreeBSD/Linux Kernel Cross Reference
sys/kern/kern_syscalls.c