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1 | .\" -*- nroff -*- |
2 | .\" | |
3 | .\" Copyright (C) 1995 Michael Shields <shields@tembel.org>. | |
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. | |
13 | .\" | |
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15 | .\" manual page may be incorrect or out-of-date.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. | |
21 | .\" | |
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> | |
29 | .\" | |
30 | .TH MPROTECT 2 2003-08-24 "Linux 2.4" "Linux Programmer's Manual" | |
31 | .SH NAME | |
32 | mprotect \- control allowable accesses to a region of memory | |
33 | .SH SYNOPSIS | |
34 | .nf | |
35 | .B #include <sys/mman.h> | |
36 | .sp | |
37 | \fBint mprotect(const void *\fIaddr\fB, size_t \fIlen\fB, int \fIprot\fB); | |
38 | .fi | |
39 | .SH DESCRIPTION | |
40 | The function | |
e511ffb6 | 41 | .BR mprotect () |
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42 | specifies the desired protection for the memory page(s) containing |
43 | part or all of the interval [\fIaddr\fP,\fIaddr\fP+\fIlen\fP-1]. | |
44 | If an access is disallowed by the protection given it, the program receives a | |
45 | .BR SIGSEGV . | |
46 | .PP | |
47 | .I prot | |
48 | is a bitwise-or of the following values: | |
49 | .TP 1.1i | |
50 | .B PROT_NONE | |
51 | The memory cannot be accessed at all. | |
52 | .TP | |
53 | .B PROT_READ | |
54 | The memory can be read. | |
55 | .TP | |
56 | .B PROT_WRITE | |
57 | The memory can be written to. | |
58 | .TP | |
59 | .B PROT_EXEC | |
60 | The memory can contain executing code. | |
61 | .PP | |
62 | The new protection replaces any existing protection. For example, if the | |
e511ffb6 | 63 | memory had previously been marked \fBPROT_READ\fR, and \fBmprotect\fR() |
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64 | is then called with \fIprot\fR \fBPROT_WRITE\fR, it will no longer |
65 | be readable. | |
66 | .SH "RETURN VALUE" | |
67 | On success, | |
e511ffb6 | 68 | .BR mprotect () |
fea681da MK |
69 | returns zero. On error, \-1 is returned, and |
70 | .I errno | |
71 | is set appropriately. | |
72 | .SH ERRORS | |
73 | .TP | |
74 | .B EACCES | |
75 | The memory cannot be given the specified access. This can happen, | |
76 | for example, if you | |
77 | .BR mmap (2) | |
78 | a file to which you have read-only access, then ask | |
e511ffb6 | 79 | .BR mprotect () |
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80 | to mark it |
81 | .BR PROT_WRITE . | |
82 | .TP | |
83 | .B EFAULT | |
84 | The memory cannot be accessed. | |
85 | .TP | |
86 | .B EINVAL | |
87 | \fIaddr\fR is not a valid pointer, or not a multiple of PAGESIZE. | |
88 | .TP | |
89 | .B ENOMEM | |
f8ad0aeb | 90 | Internal kernel structures could not be allocated. |
c8a55a3d | 91 | Or: addresses in the range |
f8ad0aeb MK |
92 | .RI [ addr , |
93 | .IR addr + len ] | |
94 | are invalid for the address space of the process, | |
95 | or specify one or more pages that are not mapped. | |
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96 | .SH EXAMPLE |
97 | .nf | |
98 | #include <stdio.h> | |
99 | #include <stdlib.h> | |
100 | #include <errno.h> | |
101 | #include <sys/mman.h> | |
102 | ||
103 | #include <limits.h> /* for PAGESIZE */ | |
104 | #ifndef PAGESIZE | |
105 | #define PAGESIZE 4096 | |
106 | #endif | |
107 | ||
108 | int | |
109 | main(void) | |
110 | { | |
111 | char *p; | |
112 | char c; | |
113 | ||
114 | /* Allocate a buffer; it will have the default | |
115 | protection of PROT_READ|PROT_WRITE. */ | |
116 | p = malloc(1024+PAGESIZE-1); | |
117 | if (!p) { | |
118 | perror("Couldn't malloc(1024)"); | |
119 | exit(errno); | |
120 | } | |
121 | ||
122 | /* Align to a multiple of PAGESIZE, assumed to be a power of two */ | |
123 | p = (char *)(((int) p + PAGESIZE-1) & ~(PAGESIZE-1)); | |
124 | ||
125 | c = p[666]; /* Read; ok */ | |
126 | p[666] = 42; /* Write; ok */ | |
127 | ||
128 | /* Mark the buffer read-only. */ | |
129 | if (mprotect(p, 1024, PROT_READ)) { | |
130 | perror("Couldn't mprotect"); | |
131 | exit(errno); | |
132 | } | |
133 | ||
134 | c = p[666]; /* Read; ok */ | |
135 | p[666] = 42; /* Write; program dies on SIGSEGV */ | |
136 | ||
137 | exit(0); | |
138 | } | |
139 | .fi | |
140 | .SH "CONFORMING TO" | |
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141 | SVr4, POSIX.1-2001. |
142 | .\" SVr4 defines an additional error | |
143 | .\" code EAGAIN. The SVr4 error conditions don't map neatly onto Linux's. | |
fea681da | 144 | POSIX says that |
e511ffb6 | 145 | .BR mprotect () |
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146 | can be used only on regions of memory obtained from |
147 | .BR mmap (2). | |
148 | .SH NOTES | |
149 | On Linux it is always legal to call | |
e511ffb6 | 150 | .BR mprotect () |
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151 | on any address in a process' address space (except for the |
152 | kernel vsyscall area). In particular it can be used | |
153 | to change existing code mappings to be writable. | |
154 | ||
155 | Whether | |
156 | .B PROT_EXEC | |
157 | has any effect different from | |
158 | .B PROT_READ | |
159 | is architecture and kernel version dependent. | |
160 | .SH "SEE ALSO" | |
161 | .BR mmap (2) |