The mprotect() function shall change the access protections to be that
specified by prot for those whole pages containing any part of the
address space of the process starting at address addr and continuing
for len bytes. The parameter prot determines whether read,
write, execute, or some combination of accesses are permitted to the data
being mapped. The prot argument should be either PROT_NONE or the
bitwise-inclusive OR of one or more of PROT_READ, PROT_WRITE, and PROT_EXEC.
If an implementation cannot support the combination of access types specified by
prot, the call to mprotect() shall fail.
An implementation may permit accesses other than those specified by prot;
however, no implementation shall permit a write to succeed where PROT_WRITE
has not been set or shall permit any access where PROT_NONE alone has been
set. Implementations shall support at least the following values of
prot: PROT_NONE, PROT_READ, PROT_WRITE, and the bitwise-inclusive OR of
PROT_READ and PROT_WRITE. If PROT_WRITE is specified, the application shall
ensure that it has opened the mapped objects in the specified address range
with write permission, unless MAP_PRIVATE was specified in the original
mapping, regardless of whether the file descriptors used to map the objects
have since been closed.
The implementation shall require that addr be a multiple of the page size
as returned by sysconf().
The behavior of this function is unspecified if the mapping was not established
by a call to mmap().
When mprotect() fails for reasons other than [EINVAL], the protections on
some of the pages in the range [ addr,addr+len) may have
Portions of this text are reprinted and reproduced in electronic form from IEEE
Std 1003.1, 2003 Edition, Standard for Information Technology -- Portable
Operating System Interface (POSIX), The Open Group Base Specifications Issue
6, Copyright (C) 2001-2003 by the Institute of Electrical and Electronics
Engineers, Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard, the original
IEEE and The Open Group Standard is the referee document. The original
Standard can be obtained online at http://www.opengroup.org/unix/online.html