MPROTECT(P) POSIX Programmer's Manual MPROTECT(P)
mprotect - set protection of memory mapping
int mprotect(void *addr, size_t len, int prot);
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, exe-
cute, 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 fol-
lowing values of prot: PROT_NONE, PROT_READ, PROT_WRITE, and the bitwise-inclusive OR of PROT_READ and PROT_WRITE. If PROT_WRITE is speci-
fied, 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
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 been
Upon successful completion, mprotect() shall return 0; otherwise, it shall return -1 and set errno to indicate the error.
The mprotect() function shall fail if:
EACCES The prot argument specifies a protection that violates the access permission the process has to the underlying memory object.
EAGAIN The prot argument specifies PROT_WRITE over a MAP_PRIVATE mapping and there are insufficient memory resources to reserve for locking
the private page.
EINVAL The addr argument is not a multiple of the page size as returned by sysconf().
ENOMEM Addresses in the range [addr,addr+len) are invalid for the address space of a process, or specify one or more pages which are not
ENOMEM The prot argument specifies PROT_WRITE on a MAP_PRIVATE mapping, and it would require more space than the system is able to supply
for locking the private pages, if required.
The implementation does not support the combination of accesses requested in the prot argument.
The following sections are informative.
The [EINVAL] error above is marked EX because it is defined as an optional error in the POSIX Realtime Extension.
mmap() , sysconf() , the Base Definitions volume of IEEE Std 1003.1-2001, <sys/mman.h>
Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1, 2003 Edition, Standard for Information Technol-
ogy -- 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 .
/The Open Group 2003 MPROTECT(P)