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c13182ef | 1 | .\" -*- nroff -*- |
c11b1abf | 2 | .\" Copyright (C) 2007 Michael Kerrisk <mtk.manpages@gmail.com> |
2a5e0dcd | 3 | .\" and Copyright (C) 1995 Michael Shields <shields@tembel.org>. |
fea681da MK |
4 | .\" |
5 | .\" Permission is granted to make and distribute verbatim copies of this | |
6 | .\" manual provided the copyright notice and this permission notice are | |
7 | .\" preserved on all copies. | |
8 | .\" | |
9 | .\" Permission is granted to copy and distribute modified versions of this | |
10 | .\" manual under the conditions for verbatim copying, provided that the | |
11 | .\" entire resulting derived work is distributed under the terms of a | |
12 | .\" permission notice identical to this one. | |
c13182ef | 13 | .\" |
fea681da MK |
14 | .\" Since the Linux kernel and libraries are constantly changing, this |
15 | .\" manual page may be incorrect or out-of-date. The author(s) assume no | |
16 | .\" responsibility for errors or omissions, or for damages resulting from | |
17 | .\" the use of the information contained herein. The author(s) may not | |
18 | .\" have taken the same level of care in the production of this manual, | |
19 | .\" which is licensed free of charge, as they might when working | |
20 | .\" professionally. | |
c13182ef | 21 | .\" |
fea681da MK |
22 | .\" Formatted or processed versions of this manual, if unaccompanied by |
23 | .\" the source, must acknowledge the copyright and author of this work. | |
24 | .\" | |
25 | .\" Modified 1996-10-22 by Eric S. Raymond <esr@thyrsus.com> | |
26 | .\" Modified 1997-05-31 by Andries Brouwer <aeb@cwi.nl> | |
27 | .\" Modified 2003-08-24 by Andries Brouwer <aeb@cwi.nl> | |
28 | .\" Modified 2004-08-16 by Andi Kleen <ak@muc.de> | |
2a5e0dcd MK |
29 | .\" 2007-06-02, mtk: Fairly substantial rewrites and additions, and |
30 | .\" a much improved example program. | |
fea681da | 31 | .\" |
87e5ebf9 | 32 | .TH MPROTECT 2 2011-09-08 "Linux" "Linux Programmer's Manual" |
fea681da | 33 | .SH NAME |
2a5e0dcd | 34 | mprotect \- set protection on a region of memory |
fea681da MK |
35 | .SH SYNOPSIS |
36 | .nf | |
37 | .B #include <sys/mman.h> | |
38 | .sp | |
a2f11be3 | 39 | .BI "int mprotect(void *" addr ", size_t " len ", int " prot ); |
fea681da MK |
40 | .fi |
41 | .SH DESCRIPTION | |
e511ffb6 | 42 | .BR mprotect () |
2a5e0dcd | 43 | changes protection for the calling process's memory page(s) |
988db661 | 44 | containing any part of the address range in the |
657e762d | 45 | interval [\fIaddr\fP,\ \fIaddr\fP+\fIlen\fP\-1]. |
2a5e0dcd MK |
46 | .I addr |
47 | must be aligned to a page boundary. | |
48 | ||
49 | If the calling process tries to access memory in a manner | |
988db661 | 50 | that violates the protection, then the kernel generates a |
2a5e0dcd MK |
51 | .B SIGSEGV |
52 | signal for the process. | |
fea681da MK |
53 | .PP |
54 | .I prot | |
2a5e0dcd MK |
55 | is either |
56 | .B PROT_NONE | |
57 | or a bitwise-or of the other values in the following list: | |
fea681da MK |
58 | .TP 1.1i |
59 | .B PROT_NONE | |
60 | The memory cannot be accessed at all. | |
61 | .TP | |
62 | .B PROT_READ | |
63 | The memory can be read. | |
64 | .TP | |
65 | .B PROT_WRITE | |
2a5e0dcd | 66 | The memory can be modified. |
fea681da MK |
67 | .TP |
68 | .B PROT_EXEC | |
fc15ae54 | 69 | The memory can be executed. |
e7d3b070 | 70 | .\" FIXME |
2b83e9fe | 71 | .\" Document PROT_GROWSUP and PROT_GROWSDOWN |
fea681da MK |
72 | .SH "RETURN VALUE" |
73 | On success, | |
e511ffb6 | 74 | .BR mprotect () |
c13182ef MK |
75 | returns zero. |
76 | On error, \-1 is returned, and | |
fea681da MK |
77 | .I errno |
78 | is set appropriately. | |
79 | .SH ERRORS | |
80 | .TP | |
81 | .B EACCES | |
c13182ef MK |
82 | The memory cannot be given the specified access. |
83 | This can happen, for example, if you | |
fea681da MK |
84 | .BR mmap (2) |
85 | a file to which you have read-only access, then ask | |
e511ffb6 | 86 | .BR mprotect () |
fea681da MK |
87 | to mark it |
88 | .BR PROT_WRITE . | |
89 | .TP | |
fea681da | 90 | .B EINVAL |
a8d55537 | 91 | \fIaddr\fP is not a valid pointer, |
2a5e0dcd | 92 | or not a multiple of the system page size. |
3a928a50 | 93 | .\" Or: both PROT_GROWSUP and PROT_GROWSDOWN were specified in 'prot'. |
fea681da MK |
94 | .TP |
95 | .B ENOMEM | |
c13182ef | 96 | Internal kernel structures could not be allocated. |
22b22831 MK |
97 | .TP |
98 | .B ENOMEM | |
99 | Addresses in the range | |
f8ad0aeb | 100 | .RI [ addr , |
da2336b3 | 101 | .IR addr + len \-1] |
f8ad0aeb MK |
102 | are invalid for the address space of the process, |
103 | or specify one or more pages that are not mapped. | |
22b22831 MK |
104 | (Before kernel 2.4.19, the error |
105 | .BR EFAULT | |
106 | was incorrectly produced for these cases.) | |
2b2581ee MK |
107 | .SH "CONFORMING TO" |
108 | SVr4, POSIX.1-2001. | |
109 | .\" SVr4 defines an additional error | |
110 | .\" code EAGAIN. The SVr4 error conditions don't map neatly onto Linux's. | |
d9bfdb9c | 111 | POSIX says that the behavior of |
2b2581ee | 112 | .BR mprotect () |
2a5e0dcd MK |
113 | is unspecified if it is applied to a region of memory that |
114 | was not obtained via | |
2b2581ee MK |
115 | .BR mmap (2). |
116 | .SH NOTES | |
e935e108 | 117 | On Linux it is always permissible to call |
2b2581ee | 118 | .BR mprotect () |
fc7ba057 | 119 | on any address in a process's address space (except for the |
2b2581ee MK |
120 | kernel vsyscall area). |
121 | In particular it can be used | |
122 | to change existing code mappings to be writable. | |
123 | ||
124 | Whether | |
125 | .B PROT_EXEC | |
126 | has any effect different from | |
127 | .B PROT_READ | |
a43eed0c | 128 | is architecture- and kernel version-dependent. |
34ccb744 | 129 | On some hardware architectures (e.g., i386), |
0daa9e92 | 130 | .B PROT_WRITE |
f3edaabb MK |
131 | implies |
132 | .BR PROT_READ . | |
2a5e0dcd MK |
133 | |
134 | POSIX.1-2001 says that an implementation may permit access | |
135 | other than that specified in | |
136 | .IR prot , | |
137 | but at a minimum can only allow write access if | |
138 | .B PROT_WRITE | |
139 | has been set, and must not allow any access if | |
140 | .B PROT_NONE | |
141 | has been set. | |
fea681da | 142 | .SH EXAMPLE |
2720c2ed | 143 | .\" sigaction.2 refers to this example |
f20d7d8e | 144 | .PP |
2a5e0dcd | 145 | The program below allocates four pages of memory, makes the third |
5fab2e7c | 146 | of these pages read-only, and then executes a loop that walks upward |
f20d7d8e MK |
147 | through the allocated region modifying bytes. |
148 | ||
149 | An example of what we might see when running the program is the | |
150 | following: | |
151 | ||
088a639b | 152 | .in +4n |
fea681da | 153 | .nf |
b43a3b30 | 154 | .RB "$" " ./a.out" |
f20d7d8e MK |
155 | Start of region: 0x804c000 |
156 | Got SIGSEGV at address: 0x804e000 | |
157 | .fi | |
1c32ee47 | 158 | .in |
9c330504 | 159 | .SS Program source |
d84d0300 | 160 | \& |
f20d7d8e | 161 | .nf |
f20d7d8e MK |
162 | #include <unistd.h> |
163 | #include <signal.h> | |
fea681da | 164 | #include <stdio.h> |
f20d7d8e | 165 | #include <malloc.h> |
fea681da MK |
166 | #include <stdlib.h> |
167 | #include <errno.h> | |
168 | #include <sys/mman.h> | |
169 | ||
6a578b88 MK |
170 | #define handle_error(msg) \\ |
171 | do { perror(msg); exit(EXIT_FAILURE); } while (0) | |
d3b5ab82 | 172 | |
f20d7d8e MK |
173 | char *buffer; |
174 | ||
175 | static void | |
176 | handler(int sig, siginfo_t *si, void *unused) | |
177 | { | |
988db661 | 178 | printf("Got SIGSEGV at address: 0x%lx\\n", |
29059a65 | 179 | (long) si\->si_addr); |
f20d7d8e MK |
180 | exit(EXIT_FAILURE); |
181 | } | |
fea681da MK |
182 | |
183 | int | |
f20d7d8e | 184 | main(int argc, char *argv[]) |
fea681da MK |
185 | { |
186 | char *p; | |
f20d7d8e MK |
187 | int pagesize; |
188 | struct sigaction sa; | |
189 | ||
190 | sa.sa_flags = SA_SIGINFO; | |
191 | sigemptyset(&sa.sa_mask); | |
192 | sa.sa_sigaction = handler; | |
29059a65 | 193 | if (sigaction(SIGSEGV, &sa, NULL) == \-1) |
6a578b88 | 194 | handle_error("sigaction"); |
fea681da | 195 | |
f20d7d8e | 196 | pagesize = sysconf(_SC_PAGE_SIZE); |
29059a65 | 197 | if (pagesize == \-1) |
6a578b88 | 198 | handle_error("sysconf"); |
fea681da | 199 | |
988db661 | 200 | /* Allocate a buffer aligned on a page boundary; |
f20d7d8e MK |
201 | initial protection is PROT_READ | PROT_WRITE */ |
202 | ||
203 | buffer = memalign(pagesize, 4 * pagesize); | |
d3b5ab82 | 204 | if (buffer == NULL) |
6a578b88 | 205 | handle_error("memalign"); |
fea681da | 206 | |
f20d7d8e | 207 | printf("Start of region: 0x%lx\\n", (long) buffer); |
fea681da | 208 | |
988db661 | 209 | if (mprotect(buffer + pagesize * 2, pagesize, |
7d9da03f | 210 | PROT_READ) == \-1) |
6a578b88 | 211 | handle_error("mprotect"); |
fea681da | 212 | |
f20d7d8e | 213 | for (p = buffer ; ; ) |
f81fb444 | 214 | *(p++) = \(aqa\(aq; |
fea681da | 215 | |
f20d7d8e | 216 | printf("Loop completed\\n"); /* Should never happen */ |
646f46f0 | 217 | exit(EXIT_SUCCESS); |
fea681da MK |
218 | } |
219 | .fi | |
fea681da | 220 | .SH "SEE ALSO" |
2a5e0dcd MK |
221 | .BR mmap (2), |
222 | .BR sysconf (3) |