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.\" $OpenBSD: mprotect.2,v 1.26 2021/06/30 18:46:49 schwarze Exp $
.\" $NetBSD: mprotect.2,v 1.6 1995/10/12 15:41:08 jtc Exp $
.\"
.\" Copyright (c) 1991, 1993
.\" The Regents of the University of California. All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\" notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\" notice, this list of conditions and the following disclaimer in the
.\" documentation and/or other materials provided with the distribution.
.\" 3. Neither the name of the University nor the names of its contributors
.\" may be used to endorse or promote products derived from this software
.\" without specific prior written permission.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE REGENTS AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
.\"
.\" @(#)mprotect.2 8.1 (Berkeley) 6/9/93
.\"
.Dd $Mdocdate: June 30 2021 $
.Dt MPROTECT 2
.Os
.Sh NAME
.Nm mprotect
.Nd control the protection of pages
.Sh SYNOPSIS
.In sys/mman.h
.Ft int
.Fn mprotect "void *addr" "size_t len" "int prot"
.Sh DESCRIPTION
The
.Fn mprotect
system call sets the access protections for the pages that contain
the address range
.Fa addr
through
.Fa addr
\&+
.Fa len
\- 1
(inclusive).
If
.Fa len
is 0, no action is taken on the page that contains
.Fa addr .
.Pp
The protections (region accessibility) are specified in the
.Fa prot
argument.
It should either be
.Dv PROT_NONE
.Pq no permissions
or the bitwise OR of one or more of the following values:
.Pp
.Bl -tag -width "PROT_WRITEXX" -offset indent -compact
.It Dv PROT_EXEC
Pages may be executed.
.It Dv PROT_READ
Pages may be read.
.It Dv PROT_WRITE
Pages may be written.
.El
.Pp
Not all implementations will guarantee protection on a page basis;
the granularity of protection changes may be as large as an entire region.
Nor will all implementations guarantee to give exactly the requested
permissions; more permissions may be granted than requested by
.Fa prot .
However, if
.Dv PROT_WRITE
was not specified then the page will not be writable.
.Sh RETURN VALUES
.Rv -std
.Sh ERRORS
.Fn mprotect
will fail if:
.Bl -tag -width Er
.It Bq Er EACCES
The process does not have sufficient access to the underlying memory
object to provide the requested protection.
.It Bq Er ENOMEM
The process has locked future pages with
.Fn mlockall MCL_FUTURE ,
a page being protected is not currently accessible,
and making it accessible and locked would exceed process or system limits.
.It Bq Er ENOTSUP
The accesses requested in the
.Fa prot
argument are not allowed.
In particular,
.Dv PROT_WRITE | PROT_EXEC
mappings are not permitted in most binaries (see
.Dv kern.wxabort
in
.Xr sysctl 2
for more information).
.It Bq Er EINVAL
The
.Fa prot
argument is invalid or the specified address range would wrap around.
.El
.Sh SEE ALSO
.Xr madvise 2 ,
.Xr msync 2 ,
.Xr munmap 2
.Sh STANDARDS
The
.Fn mprotect
function conforms to
.St -p1003.1-2008 .
.Sh HISTORY
The
.Fn mprotect
function has been available since
.Bx 4.3 Net/2 .
.Sh CAVEATS
The
.Ox
implementation of
.Fn mprotect
does not require
.Fa addr
to be page-aligned,
although other implementations may.
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