1 /*-
2 * Copyright (c) 1999 Assar Westerlund
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 * notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 * notice, this list of conditions and the following disclaimer in the
12 * documentation and/or other materials provided with the distribution.
13 *
14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
15 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
17 * ARE DISCLAIMED. IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
18 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
19 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
20 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
21 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
22 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
23 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
24 * SUCH DAMAGE.
25 */
26
27 #include <sys/cdefs.h>
28 __FBSDID("$FreeBSD: releng/11.1/sys/kern/kern_syscalls.c 284215 2015-06-10 10:48:12Z mjg $");
29
30 #include <sys/param.h>
31 #include <sys/kernel.h>
32 #include <sys/lock.h>
33 #include <sys/module.h>
34 #include <sys/mutex.h>
35 #include <sys/proc.h>
36 #include <sys/resourcevar.h>
37 #include <sys/sx.h>
38 #include <sys/syscall.h>
39 #include <sys/sysent.h>
40 #include <sys/sysproto.h>
41 #include <sys/systm.h>
42 #include <machine/atomic.h>
43
44 /*
45 * Acts like "nosys" but can be identified in sysent for dynamic call
46 * number assignment for a limited number of calls.
47 *
48 * Place holder for system call slots reserved for loadable modules.
49 */
50 int
51 lkmnosys(struct thread *td, struct nosys_args *args)
52 {
53
54 return (nosys(td, args));
55 }
56
57 int
58 lkmressys(struct thread *td, struct nosys_args *args)
59 {
60
61 return (nosys(td, args));
62 }
63
64 static void
65 syscall_thread_drain(struct sysent *se)
66 {
67 u_int32_t cnt, oldcnt;
68
69 do {
70 oldcnt = se->sy_thrcnt;
71 KASSERT((oldcnt & SY_THR_STATIC) == 0,
72 ("drain on static syscall"));
73 cnt = oldcnt | SY_THR_DRAINING;
74 } while (atomic_cmpset_acq_32(&se->sy_thrcnt, oldcnt, cnt) == 0);
75 while (atomic_cmpset_32(&se->sy_thrcnt, SY_THR_DRAINING,
76 SY_THR_ABSENT) == 0)
77 pause("scdrn", hz/2);
78 }
79
80 int
81 syscall_thread_enter(struct thread *td, struct sysent *se)
82 {
83 u_int32_t cnt, oldcnt;
84
85 do {
86 oldcnt = se->sy_thrcnt;
87 if ((oldcnt & SY_THR_STATIC) != 0)
88 return (0);
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 if ((oldcnt & SY_THR_STATIC) != 0)
104 return;
105 cnt = oldcnt - SY_THR_INCR;
106 } while (atomic_cmpset_rel_32(&se->sy_thrcnt, oldcnt, cnt) == 0);
107 }
108
109 int
110 syscall_register(int *offset, struct sysent *new_sysent,
111 struct sysent *old_sysent, int flags)
112 {
113 int i;
114
115 if ((flags & ~SY_THR_STATIC) != 0)
116 return (EINVAL);
117
118 if (*offset == NO_SYSCALL) {
119 for (i = 1; i < SYS_MAXSYSCALL; ++i)
120 if (sysent[i].sy_call == (sy_call_t *)lkmnosys)
121 break;
122 if (i == SYS_MAXSYSCALL)
123 return (ENFILE);
124 *offset = i;
125 } else if (*offset < 0 || *offset >= SYS_MAXSYSCALL)
126 return (EINVAL);
127 else if (sysent[*offset].sy_call != (sy_call_t *)lkmnosys &&
128 sysent[*offset].sy_call != (sy_call_t *)lkmressys)
129 return (EEXIST);
130
131 KASSERT(sysent[*offset].sy_thrcnt == SY_THR_ABSENT,
132 ("dynamic syscall is not protected"));
133 *old_sysent = sysent[*offset];
134 new_sysent->sy_thrcnt = SY_THR_ABSENT;
135 sysent[*offset] = *new_sysent;
136 atomic_store_rel_32(&sysent[*offset].sy_thrcnt, flags);
137 return (0);
138 }
139
140 int
141 syscall_deregister(int *offset, struct sysent *old_sysent)
142 {
143 struct sysent *se;
144
145 if (*offset == 0)
146 return (0); /* XXX? */
147
148 se = &sysent[*offset];
149 if ((se->sy_thrcnt & SY_THR_STATIC) != 0)
150 return (EINVAL);
151 syscall_thread_drain(se);
152 sysent[*offset] = *old_sysent;
153 return (0);
154 }
155
156 int
157 syscall_module_handler(struct module *mod, int what, void *arg)
158 {
159 struct syscall_module_data *data = arg;
160 modspecific_t ms;
161 int error;
162
163 switch (what) {
164 case MOD_LOAD:
165 error = syscall_register(data->offset, data->new_sysent,
166 &data->old_sysent, data->flags);
167 if (error) {
168 /* Leave a mark so we know to safely unload below. */
169 data->offset = NULL;
170 return (error);
171 }
172 ms.intval = *data->offset;
173 MOD_XLOCK;
174 module_setspecific(mod, &ms);
175 MOD_XUNLOCK;
176 if (data->chainevh)
177 error = data->chainevh(mod, what, data->chainarg);
178 return (error);
179 case MOD_UNLOAD:
180 /*
181 * MOD_LOAD failed, so just return without calling the
182 * chained handler since we didn't pass along the MOD_LOAD
183 * event.
184 */
185 if (data->offset == NULL)
186 return (0);
187 if (data->chainevh) {
188 error = data->chainevh(mod, what, data->chainarg);
189 if (error)
190 return error;
191 }
192 error = syscall_deregister(data->offset, &data->old_sysent);
193 return (error);
194 default:
195 if (data->chainevh)
196 return (data->chainevh(mod, what, data->chainarg));
197 return (EOPNOTSUPP);
198 }
199
200 /* NOTREACHED */
201 }
202
203 int
204 syscall_helper_register(struct syscall_helper_data *sd, int flags)
205 {
206 struct syscall_helper_data *sd1;
207 int error;
208
209 for (sd1 = sd; sd1->syscall_no != NO_SYSCALL; sd1++) {
210 error = syscall_register(&sd1->syscall_no, &sd1->new_sysent,
211 &sd1->old_sysent, flags);
212 if (error != 0) {
213 syscall_helper_unregister(sd);
214 return (error);
215 }
216 sd1->registered = 1;
217 }
218 return (0);
219 }
220
221 int
222 syscall_helper_unregister(struct syscall_helper_data *sd)
223 {
224 struct syscall_helper_data *sd1;
225
226 for (sd1 = sd; sd1->registered != 0; sd1++) {
227 syscall_deregister(&sd1->syscall_no, &sd1->old_sysent);
228 sd1->registered = 0;
229 }
230 return (0);
231 }
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