1 /* $NetBSD: kern_module_hook.c,v 1.4 2019/12/13 08:02:53 skrll Exp $ */
2
3 /*-
4 * Copyright (c) 2019 The NetBSD Foundation, Inc.
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 NETBSD FOUNDATION, INC. AND CONTRIBUTORS
17 * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
18 * TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
19 * PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
20 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
21 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
22 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
23 * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
24 * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
25 * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
26 * POSSIBILITY OF SUCH DAMAGE.
27 */
28
29 /*
30 * Kernel module support.
31 */
32
33 #include <sys/cdefs.h>
34 __KERNEL_RCSID(0, "$NetBSD: kern_module_hook.c,v 1.4 2019/12/13 08:02:53 skrll Exp $");
35
36 #include <sys/param.h>
37
38 #include <sys/atomic.h>
39 #include <sys/condvar.h>
40 #include <sys/module_hook.h>
41 #include <sys/mutex.h>
42 #include <sys/pserialize.h>
43
44 #include <uvm/uvm_extern.h>
45
46 /* Locking/synchronization stuff for module hooks */
47
48 static struct {
49 kmutex_t mtx;
50 kcondvar_t cv;
51 pserialize_t psz;
52 } module_hook __cacheline_aligned;
53
54 /*
55 * We use pserialize_perform() to issue a memory barrier on the current
56 * CPU and on all other CPUs so that all prior memory operations on the
57 * current CPU globally happen before all subsequent memory operations
58 * on the current CPU, as perceived by any other CPU.
59 *
60 * pserialize_perform() might be rather heavy-weight here, but it only
61 * happens during module loading, and it allows MODULE_HOOK_CALL() to
62 * work without any other memory barriers.
63 */
64
65 void
module_hook_set(bool * hooked,struct localcount * lc)66 module_hook_set(bool *hooked, struct localcount *lc)
67 {
68
69 KASSERT(kernconfig_is_held());
70 KASSERT(!*hooked);
71
72 localcount_init(lc);
73
74 /* Wait until setup has been witnessed by all CPUs. */
75 pserialize_perform(module_hook.psz);
76
77 /* Let others use it */
78 atomic_store_relaxed(hooked, true);
79 }
80
81 void
module_hook_unset(bool * hooked,struct localcount * lc)82 module_hook_unset(bool *hooked, struct localcount *lc)
83 {
84
85 KASSERT(kernconfig_is_held());
86 KASSERT(*hooked);
87
88 /* Get exclusive with pserialize and localcount. */
89 mutex_enter(&module_hook.mtx);
90
91 /* Prevent new calls to module_hook_tryenter(). */
92 atomic_store_relaxed(hooked, false);
93
94 /* Wait for existing calls to module_hook_tryenter(). */
95 pserialize_perform(module_hook.psz);
96
97 /* Wait for module_hook_exit. */
98 localcount_drain(lc, &module_hook.cv, &module_hook.mtx);
99
100 /* All done! */
101 mutex_exit(&module_hook.mtx);
102 localcount_fini(lc);
103 }
104
105 bool
module_hook_tryenter(bool * hooked,struct localcount * lc)106 module_hook_tryenter(bool *hooked, struct localcount *lc)
107 {
108 bool call_hook;
109 int s;
110
111 s = pserialize_read_enter();
112 call_hook = atomic_load_relaxed(hooked);
113 if (call_hook)
114 localcount_acquire(lc);
115 pserialize_read_exit(s);
116
117 return call_hook;
118 }
119
120 void
module_hook_exit(struct localcount * lc)121 module_hook_exit(struct localcount *lc)
122 {
123
124 localcount_release(lc, &module_hook.cv, &module_hook.mtx);
125 }
126
127 void
module_hook_init(void)128 module_hook_init(void)
129 {
130
131 mutex_init(&module_hook.mtx, MUTEX_DEFAULT, IPL_NONE);
132 cv_init(&module_hook.cv, "mod_hook");
133 module_hook.psz = pserialize_create();
134 }
135