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("$FreeBSD$");
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 */
50int
51lkmnosys(struct thread *td, struct nosys_args *args)
52{
53
54	return (nosys(td, args));
55}
56
57int
58lkmressys(struct thread *td, struct nosys_args *args)
59{
60
61	return (nosys(td, args));
62}
63
64static void
65syscall_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
80int
81syscall_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
96void
97syscall_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
109int
110syscall_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
140int
141syscall_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
156int
157syscall_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
203int
204syscall_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
221int
222syscall_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}
232