.\" -*- nroff -*- .\" .\" Copyright (C) 1995 Michael Shields . .\" .\" 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this one .\" .\" Since the Linux kernel and libraries are constantly changing, this .\" manual page may be incorrect or out-of-date.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. .\" .TH MPROTECT 2 "1995-06-23" "Linux 1.2" "Linux Programmer's Manual" .SH NAME mprotect \- control allowable accesses to a region of memory .SH SYNOPSIS .nf .B #include .sp \fBint mprotect(caddr_t \fIaddr\fB, size_t *\fIlen\fB, int \fIprot\fB); .fi .SH DESCRIPTION .B mprotect controls how a section of memory may be accessed. 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 0.8i .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 0.8i .B EINVAL \fIaddr\fR is not a valid pointer. .TP .B EFAULT The memory cannot be accessed. .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 ENOMEM Internal kernel structures could not be allocated. .SH EXAMPLE .nf #include #include #include #include int main(void) { char *p; char c; /* Allocate a buffer; it will have the default protection of PROT_READ|PROT_WRITE. */ p = malloc(1024); if (!p) { perror("Couldn't malloc(1024)"); exit(errno); } 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 SEE ALSO .BR mmap (2)