1/*-
2 * SPDX-License-Identifier: BSD-2-Clause
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/param.h>
30#include <sys/kernel.h>
31#include <sys/lock.h>
32#include <sys/module.h>
33#include <sys/mutex.h>
34#include <sys/proc.h>
35#include <sys/resourcevar.h>
36#include <sys/sx.h>
37#include <sys/syscall.h>
38#include <sys/sysent.h>
39#include <sys/sysproto.h>
40#include <sys/systm.h>
41#include <machine/atomic.h>
42
43/*
44 * Acts like "nosys" but can be identified in sysent for dynamic call
45 * number assignment for a limited number of calls.
46 *
47 * Place holder for system call slots reserved for loadable modules.
48 */
49int
50lkmnosys(struct thread *td, struct nosys_args *args)
51{
52
53	return (nosys(td, args));
54}
55
56int
57lkmressys(struct thread *td, struct nosys_args *args)
58{
59
60	return (nosys(td, args));
61}
62
63struct sysent nosys_sysent = {
64	.sy_call =	(sy_call_t *)nosys,
65	.sy_systrace_args_func = NULL,
66	.sy_narg =	0,
67	.sy_flags =	SYF_CAPENABLED,
68	.sy_auevent =	AUE_NULL,
69	.sy_entry =	0, /* DTRACE_IDNONE */
70	.sy_return =	0,
71	.sy_thrcnt =	SY_THR_STATIC,
72};
73
74static void
75syscall_thread_drain(struct sysent *se)
76{
77	uint32_t cnt, oldcnt;
78
79	do {
80		oldcnt = se->sy_thrcnt;
81		KASSERT((oldcnt & SY_THR_STATIC) == 0,
82		    ("drain on static syscall"));
83		cnt = oldcnt | SY_THR_DRAINING;
84	} while (atomic_cmpset_acq_32(&se->sy_thrcnt, oldcnt, cnt) == 0);
85	while (atomic_cmpset_32(&se->sy_thrcnt, SY_THR_DRAINING,
86	    SY_THR_ABSENT) == 0)
87		pause("scdrn", hz/2);
88}
89
90int
91syscall_thread_enter(struct thread *td, struct sysent **se)
92{
93	uint32_t cnt, oldcnt;
94
95	KASSERT(((*se)->sy_thrcnt & SY_THR_STATIC) == 0,
96	    ("%s: not a static syscall", __func__));
97
98	do {
99		oldcnt = (*se)->sy_thrcnt;
100		if ((oldcnt & (SY_THR_DRAINING | SY_THR_ABSENT)) != 0) {
101			*se = &nosys_sysent;
102			return (0);
103		}
104		cnt = oldcnt + SY_THR_INCR;
105	} while (atomic_cmpset_acq_32(&(*se)->sy_thrcnt, oldcnt, cnt) == 0);
106	return (0);
107}
108
109void
110syscall_thread_exit(struct thread *td, struct sysent *se)
111{
112	uint32_t cnt, oldcnt;
113
114	KASSERT((se->sy_thrcnt & SY_THR_STATIC) == 0,
115	    ("%s: not a static syscall", __func__));
116
117	do {
118		oldcnt = se->sy_thrcnt;
119		cnt = oldcnt - SY_THR_INCR;
120	} while (atomic_cmpset_rel_32(&se->sy_thrcnt, oldcnt, cnt) == 0);
121}
122
123int
124kern_syscall_register(struct sysent *sysents, int *offset,
125    struct sysent *new_sysent, struct sysent *old_sysent, int flags)
126{
127	int i;
128
129	if ((flags & ~SY_THR_STATIC) != 0)
130		return (EINVAL);
131
132	if (*offset == NO_SYSCALL) {
133		for (i = 1; i < SYS_MAXSYSCALL; ++i)
134			if (sysents[i].sy_call == (sy_call_t *)lkmnosys)
135				break;
136		if (i == SYS_MAXSYSCALL)
137			return (ENFILE);
138		*offset = i;
139	} else if (*offset < 0 || *offset >= SYS_MAXSYSCALL) {
140		return (EINVAL);
141	} else if (sysents[*offset].sy_call != (sy_call_t *)lkmnosys &&
142	    sysents[*offset].sy_call != (sy_call_t *)lkmressys) {
143		KASSERT(sysents[*offset].sy_call != NULL,
144		    ("undefined syscall %d", *offset));
145		return (EEXIST);
146	}
147
148	KASSERT(sysents[*offset].sy_thrcnt == SY_THR_ABSENT,
149	    ("dynamic syscall is not protected"));
150	*old_sysent = sysents[*offset];
151	new_sysent->sy_thrcnt = SY_THR_ABSENT;
152	sysents[*offset] = *new_sysent;
153	atomic_store_rel_32(&sysents[*offset].sy_thrcnt, flags);
154	return (0);
155}
156
157int
158kern_syscall_deregister(struct sysent *sysents, int offset,
159    const struct sysent *old_sysent)
160{
161	struct sysent *se;
162
163	if (offset == 0)
164		return (0); /* XXX? */
165
166	se = &sysents[offset];
167	if ((se->sy_thrcnt & SY_THR_STATIC) != 0)
168		return (EINVAL);
169	syscall_thread_drain(se);
170	sysents[offset] = *old_sysent;
171	return (0);
172}
173
174int
175syscall_module_handler(struct module *mod, int what, void *arg)
176{
177
178	return (kern_syscall_module_handler(sysent, mod, what, arg));
179}
180
181int
182kern_syscall_module_handler(struct sysent *sysents, struct module *mod,
183    int what, void *arg)
184{
185	struct syscall_module_data *data = arg;
186	modspecific_t ms;
187	int error;
188
189	bzero(&ms, sizeof(ms));
190	switch (what) {
191	case MOD_LOAD:
192		error = kern_syscall_register(sysents, data->offset,
193		    data->new_sysent, &data->old_sysent, data->flags);
194		if (error) {
195			/* Leave a mark so we know to safely unload below. */
196			data->offset = NULL;
197			return (error);
198		}
199		ms.intval = *data->offset;
200		MOD_XLOCK;
201		module_setspecific(mod, &ms);
202		MOD_XUNLOCK;
203		if (data->chainevh)
204			error = data->chainevh(mod, what, data->chainarg);
205		return (error);
206	case MOD_UNLOAD:
207		/*
208		 * MOD_LOAD failed, so just return without calling the
209		 * chained handler since we didn't pass along the MOD_LOAD
210		 * event.
211		 */
212		if (data->offset == NULL)
213			return (0);
214		if (data->chainevh) {
215			error = data->chainevh(mod, what, data->chainarg);
216			if (error)
217				return error;
218		}
219		error = kern_syscall_deregister(sysents, *data->offset,
220		    &data->old_sysent);
221		return (error);
222	default:
223		if (data->chainevh)
224			return (data->chainevh(mod, what, data->chainarg));
225		return (EOPNOTSUPP);
226	}
227
228	/* NOTREACHED */
229}
230
231int
232syscall_helper_register(struct syscall_helper_data *sd, int flags)
233{
234
235	return (kern_syscall_helper_register(sysent, sd, flags));
236}
237
238int
239kern_syscall_helper_register(struct sysent *sysents,
240    struct syscall_helper_data *sd, int flags)
241{
242	struct syscall_helper_data *sd1;
243	int error;
244
245	for (sd1 = sd; sd1->syscall_no != NO_SYSCALL; sd1++) {
246		error = kern_syscall_register(sysents, &sd1->syscall_no,
247		    &sd1->new_sysent, &sd1->old_sysent, flags);
248		if (error != 0) {
249			kern_syscall_helper_unregister(sysents, sd);
250			return (error);
251		}
252		sd1->registered = 1;
253	}
254	return (0);
255}
256
257int
258syscall_helper_unregister(struct syscall_helper_data *sd)
259{
260
261	return (kern_syscall_helper_unregister(sysent, sd));
262}
263
264int
265kern_syscall_helper_unregister(struct sysent *sysents,
266    struct syscall_helper_data *sd)
267{
268	struct syscall_helper_data *sd1;
269
270	for (sd1 = sd; sd1->registered != 0; sd1++) {
271		kern_syscall_deregister(sysents, sd1->syscall_no,
272		    &sd1->old_sysent);
273		sd1->registered = 0;
274	}
275	return (0);
276}
277