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         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_DRAINING | SY_THR_ABSENT)) != 0)
   90                         return (ENOSYS);
   91                 cnt = oldcnt + SY_THR_INCR;
   92         } while (atomic_cmpset_acq_32(&se->sy_thrcnt, oldcnt, cnt) == 0);
   93         return (0);
   94 }
   95 
   96 void
   97 _syscall_thread_exit(struct thread *td, struct sysent *se)
   98 {
   99         u_int32_t cnt, oldcnt;
  100 
  101         do {
  102                 oldcnt = se->sy_thrcnt;
  103                 cnt = oldcnt - SY_THR_INCR;
  104         } while (atomic_cmpset_rel_32(&se->sy_thrcnt, oldcnt, cnt) == 0);
  105 }
  106 
  107 int
  108 kern_syscall_register(struct sysent *sysents, int *offset,
  109     struct sysent *new_sysent, struct sysent *old_sysent, int flags)
  110 {
  111         int i;
  112 
  113         if ((flags & ~SY_THR_STATIC) != 0)
  114                 return (EINVAL);
  115 
  116         if (*offset == NO_SYSCALL) {
  117                 for (i = 1; i < SYS_MAXSYSCALL; ++i)
  118                         if (sysents[i].sy_call == (sy_call_t *)lkmnosys)
  119                                 break;
  120                 if (i == SYS_MAXSYSCALL)
  121                         return (ENFILE);
  122                 *offset = i;
  123         } else if (*offset < 0 || *offset >= SYS_MAXSYSCALL)
  124                 return (EINVAL);
  125         else if (sysents[*offset].sy_call != (sy_call_t *)lkmnosys &&
  126             sysents[*offset].sy_call != (sy_call_t *)lkmressys)
  127                 return (EEXIST);
  128 
  129         KASSERT(sysents[*offset].sy_thrcnt == SY_THR_ABSENT,
  130             ("dynamic syscall is not protected"));
  131         *old_sysent = sysents[*offset];
  132         new_sysent->sy_thrcnt = SY_THR_ABSENT;
  133         sysents[*offset] = *new_sysent;
  134         atomic_store_rel_32(&sysents[*offset].sy_thrcnt, flags);
  135         return (0);
  136 }
  137 
  138 int
  139 kern_syscall_deregister(struct sysent *sysents, int offset,
  140     const struct sysent *old_sysent)
  141 {
  142         struct sysent *se;
  143 
  144         if (offset == 0)
  145                 return (0); /* XXX? */
  146 
  147         se = &sysents[offset];
  148         if ((se->sy_thrcnt & SY_THR_STATIC) != 0)
  149                 return (EINVAL);
  150         syscall_thread_drain(se);
  151         sysents[offset] = *old_sysent;
  152         return (0);
  153 }
  154 
  155 int
  156 syscall_module_handler(struct module *mod, int what, void *arg)
  157 {
  158 
  159         return (kern_syscall_module_handler(sysent, mod, what, arg));
  160 }
  161 
  162 int
  163 kern_syscall_module_handler(struct sysent *sysents, struct module *mod,
  164     int what, void *arg)
  165 {
  166         struct syscall_module_data *data = arg;
  167         modspecific_t ms;
  168         int error;
  169 
  170         switch (what) {
  171         case MOD_LOAD:
  172                 error = kern_syscall_register(sysents, data->offset,
  173                     data->new_sysent, &data->old_sysent, data->flags);
  174                 if (error) {
  175                         /* Leave a mark so we know to safely unload below. */
  176                         data->offset = NULL;
  177                         return (error);
  178                 }
  179                 ms.intval = *data->offset;
  180                 MOD_XLOCK;
  181                 module_setspecific(mod, &ms);
  182                 MOD_XUNLOCK;
  183                 if (data->chainevh)
  184                         error = data->chainevh(mod, what, data->chainarg);
  185                 return (error);
  186         case MOD_UNLOAD:
  187                 /*
  188                  * MOD_LOAD failed, so just return without calling the
  189                  * chained handler since we didn't pass along the MOD_LOAD
  190                  * event.
  191                  */
  192                 if (data->offset == NULL)
  193                         return (0);
  194                 if (data->chainevh) {
  195                         error = data->chainevh(mod, what, data->chainarg);
  196                         if (error)
  197                                 return error;
  198                 }
  199                 error = kern_syscall_deregister(sysents, *data->offset,
  200                     &data->old_sysent);
  201                 return (error);
  202         default:
  203                 if (data->chainevh)
  204                         return (data->chainevh(mod, what, data->chainarg));
  205                 return (EOPNOTSUPP);
  206         }
  207 
  208         /* NOTREACHED */
  209 }
  210 
  211 int
  212 syscall_helper_register(struct syscall_helper_data *sd, int flags)
  213 {
  214 
  215         return (kern_syscall_helper_register(sysent, sd, flags));
  216 }
  217 
  218 int
  219 kern_syscall_helper_register(struct sysent *sysents,
  220     struct syscall_helper_data *sd, int flags)
  221 {
  222         struct syscall_helper_data *sd1;
  223         int error;
  224 
  225         for (sd1 = sd; sd1->syscall_no != NO_SYSCALL; sd1++) {
  226                 error = kern_syscall_register(sysents, &sd1->syscall_no,
  227                     &sd1->new_sysent, &sd1->old_sysent, flags);
  228                 if (error != 0) {
  229                         kern_syscall_helper_unregister(sysents, sd);
  230                         return (error);
  231                 }
  232                 sd1->registered = 1;
  233         }
  234         return (0);
  235 }
  236 
  237 int
  238 syscall_helper_unregister(struct syscall_helper_data *sd)
  239 {
  240 
  241         return (kern_syscall_helper_unregister(sysent, sd));
  242 }
  243 
  244 int
  245 kern_syscall_helper_unregister(struct sysent *sysents,
  246     struct syscall_helper_data *sd)
  247 {
  248         struct syscall_helper_data *sd1;
  249 
  250         for (sd1 = sd; sd1->registered != 0; sd1++) {
  251                 kern_syscall_deregister(sysents, sd1->syscall_no,
  252                     &sd1->old_sysent);
  253                 sd1->registered = 0;
  254         }
  255         return (0);
  256 }

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

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