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.\"	@(#)mprotect.2	8.1 (Berkeley) 6/9/93
.\"
.Dd February 26, 2020
.Dt MPROTECT 2
.Os
.Sh NAME
.Nm mprotect
.Nd control the protection of pages
.Sh LIBRARY
.Lb libc
.Sh SYNOPSIS
.In sys/mman.h
.Ft int
.Fn mprotect "void *addr" "size_t len" "int prot"
.Sh DESCRIPTION
The
.Fn mprotect
system call
changes the specified pages to have protection
.Fa prot .
Not all implementations will guarantee protection on a page basis;
the granularity of protection changes may be as large as an entire region.
A region is the virtual address space defined by the start
and end addresses of a
.Vt "struct vm_map_entry" .
.Pp
Currently these protection bits are known,
which can be combined, OR'd together:
.Pp
.Bl -tag -width ".Dv PROT_WRITE" -compact
.It Dv PROT_NONE
No permissions at all.
.It Dv PROT_READ
The pages can be read.
.It Dv PROT_WRITE
The pages can be written.
.It Dv PROT_EXEC
The pages can be executed.
.El
.Pp
In addition to these protection flags,
.Fx
provides the ability to set the maximum protection of a region
(which prevents
.Nm
from upgrading the permissions).
This is accomplished by
.Em or Ns 'ing
one or more
.Dv PROT_
values wrapped in the
.Dv PROT_MAX()
macro into the
.Fa prot
argument.
.Sh RETURN VALUES
.Rv -std mprotect
.Sh ERRORS
The
.Fn mprotect
system call will fail if:
.Bl -tag -width Er
.It Bq Er EACCES
The calling process was not allowed to change
the protection to the value specified by
the
.Fa prot
argument.
.It Bq Er EINVAL
The virtual address range specified by the
.Fa addr
and
.Fa len
arguments is not valid.
.It Bq Er EINVAL
The
.Fa prot
argument contains unhandled bits.
.It Bq Er ENOTSUP
The
.Fa prot
argument contains permissions which are not a subset of the specified
maximum permissions.
.El
.Sh SEE ALSO
.Xr madvise 2 ,
.Xr mincore 2 ,
.Xr msync 2 ,
.Xr munmap 2
.Sh HISTORY
The
.Fn mprotect
system call was first documented in
.Bx 4.2
and first appeared in
.Bx 4.4 .
.Pp
The
.Dv PROT_MAX
functionality was introduced in
.Fx 13 .