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Diffstat (limited to 'man2/mprotect.2')
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diff --git a/man2/mprotect.2 b/man2/mprotect.2 new file mode 100644 index 000000000..604682203 --- /dev/null +++ b/man2/mprotect.2 @@ -0,0 +1,155 @@ +.\" -*- nroff -*- +.\" +.\" Copyright (C) 1995 Michael Shields <shields@tembel.org>. +.\" +.\" Permission is granted to make and distribute verbatim copies of this +.\" manual provided the copyright notice and this permission notice are +.\" preserved on all copies. +.\" +.\" Permission is granted to copy and distribute modified versions of this +.\" manual under the conditions for verbatim copying, provided that the +.\" entire resulting derived work is distributed under the terms of a +.\" permission notice identical to this one. +.\" +.\" Since the Linux kernel and libraries are constantly changing, this +.\" manual page may be incorrect or out-of-date. The author(s) assume no +.\" responsibility for errors or omissions, or for damages resulting from +.\" the use of the information contained herein. The author(s) may not +.\" have taken the same level of care in the production of this manual, +.\" which is licensed free of charge, as they might when working +.\" professionally. +.\" +.\" Formatted or processed versions of this manual, if unaccompanied by +.\" the source, must acknowledge the copyright and author of this work. +.\" +.\" Modified 1996-10-22 by Eric S. Raymond <esr@thyrsus.com> +.\" Modified 1997-05-31 by Andries Brouwer <aeb@cwi.nl> +.\" Modified 2003-08-24 by Andries Brouwer <aeb@cwi.nl> +.\" Modified 2004-08-16 by Andi Kleen <ak@muc.de> +.\" +.TH MPROTECT 2 2003-08-24 "Linux 2.4" "Linux Programmer's Manual" +.SH NAME +mprotect \- control allowable accesses to a region of memory +.SH SYNOPSIS +.nf +.B #include <sys/mman.h> +.sp +\fBint mprotect(const void *\fIaddr\fB, size_t \fIlen\fB, int \fIprot\fB); +.fi +.SH DESCRIPTION +The function +.B mprotect +specifies the desired protection for the memory page(s) containing +part or all of the interval [\fIaddr\fP,\fIaddr\fP+\fIlen\fP-1]. +If an access is disallowed by the protection given it, the program receives a +.BR SIGSEGV . +.PP +.I prot +is a bitwise-or of the following values: +.TP 1.1i +.B PROT_NONE +The memory cannot be accessed at all. +.TP +.B PROT_READ +The memory can be read. +.TP +.B PROT_WRITE +The memory can be written to. +.TP +.B PROT_EXEC +The memory can contain executing code. +.PP +The new protection replaces any existing protection. For example, if the +memory had previously been marked \fBPROT_READ\fR, and \fBmprotect\fR +is then called with \fIprot\fR \fBPROT_WRITE\fR, it will no longer +be readable. +.SH "RETURN VALUE" +On success, +.B mprotect +returns zero. On error, \-1 is returned, and +.I errno +is set appropriately. +.SH ERRORS +.TP +.B EACCES +The memory cannot be given the specified access. This can happen, +for example, if you +.BR mmap (2) +a file to which you have read-only access, then ask +.B mprotect +to mark it +.BR PROT_WRITE . +.TP +.B EFAULT +The memory cannot be accessed. +.TP +.B EINVAL +\fIaddr\fR is not a valid pointer, or not a multiple of PAGESIZE. +.TP +.B ENOMEM +Internal kernel structures could not be allocated. +.SH EXAMPLE +.nf +#include <stdio.h> +#include <stdlib.h> +#include <errno.h> +#include <sys/mman.h> + +#include <limits.h> /* for PAGESIZE */ +#ifndef PAGESIZE +#define PAGESIZE 4096 +#endif + +int +main(void) +{ + char *p; + char c; + + /* Allocate a buffer; it will have the default + protection of PROT_READ|PROT_WRITE. */ + p = malloc(1024+PAGESIZE-1); + if (!p) { + perror("Couldn't malloc(1024)"); + exit(errno); + } + + /* Align to a multiple of PAGESIZE, assumed to be a power of two */ + p = (char *)(((int) p + PAGESIZE-1) & ~(PAGESIZE-1)); + + c = p[666]; /* Read; ok */ + p[666] = 42; /* Write; ok */ + + /* Mark the buffer read-only. */ + if (mprotect(p, 1024, PROT_READ)) { + perror("Couldn't mprotect"); + exit(errno); + } + + c = p[666]; /* Read; ok */ + p[666] = 42; /* Write; program dies on SIGSEGV */ + + exit(0); +} +.fi +.SH "CONFORMING TO" +SVr4, POSIX.1b (formerly POSIX.4). SVr4 defines an additional error +code EAGAIN. The SVr4 error conditions don't map neatly onto Linux's. +POSIX says that +.B mprotect +can be used only on regions of memory obtained from +.BR mmap (2). +.SH NOTES +On Linux it is always legal to call +.B mprotect +on any address in a process' address space (except for the +kernel vsyscall area). In particular it can be used +to change existing code mappings to be writable. + +Whether +.B PROT_EXEC +has any effect different from +.B PROT_READ +is architecture and kernel version dependent. +.SH "SEE ALSO" +.BR mmap (2) |