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 */
52int
53lkmnosys(struct thread *td, struct nosys_args *args)
54{
55
56	return (nosys(td, args));
57}
58
59int
60lkmressys(struct thread *td, struct nosys_args *args)
61{
62
63	return (nosys(td, args));
64}
65
66static void
67syscall_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
82int
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
96void
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
107int
108kern_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
138int
139kern_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
155int
156syscall_module_handler(struct module *mod, int what, void *arg)
157{
158
159	return (kern_syscall_module_handler(sysent, mod, what, arg));
160}
161
162int
163kern_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
211int
212syscall_helper_register(struct syscall_helper_data *sd, int flags)
213{
214
215	return (kern_syscall_helper_register(sysent, sd, flags));
216}
217
218int
219kern_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
237int
238syscall_helper_unregister(struct syscall_helper_data *sd)
239{
240
241	return (kern_syscall_helper_unregister(sysent, sd));
242}
243
244int
245kern_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}
257