MPROTECT(2)

NAME
mprotect - control the protection of pages

SYNOPSIS
#include <sys/mman.h>
int
mprotect(void *addr, size_t len, int prot);

DESCRIPTION
The mprotect() system call sets the access protections for the pages that contain the address range addr through addr + len - 1 (inclusive). If len is 0, no action is taken on the page that contains addr.

The protections (region accessibility) are specified in the prot argument. It should either be PROT_NONE (no permissions) or the bitwise OR of one or more of the following values:

PROT_EXEC
    Pages may be executed.
PROT_READ
    Pages may be read.
PROT_WRITE
    Pages may be written.

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 prot. However, if PROT_WRITE was not specified then the page will not be writable.

RETURN VALUES

ERRORS
mprotect() will fail if:

[EACCES]
    The process does not have sufficient access to the underlying memory object to provide the requested protection.

[ENOMEM]
    The process has locked future pages with mlockall(MCL_FUTURE), a page being protected is not currently accessible, and making it accessible and locked would exceed process or system limits.

[ENOTSUP]
    The accesses requested in the prot argument are not allowed. In particular, PROT_WRITE | PROT_EXEC mappings are not permitted in most binaries (see kern.wxabort in sysctl(2) for more information).

[EINVAL]
    The prot argument is invalid or the specified address range would wrap around.

[EPERM]
    The addr and len parameters specify a region which contains at least one page marked immutable.

SEE ALSO
madvise(2), msync(2), munmap(2)

STANDARDS
The mprotect() function conforms to p1003.1-2008.

HISTORY
The mprotect() function has been available since 4.3BSD Net/2.

CAVEATS
The OpenBSD implementation of mprotect() does not require addr to be page-aligned, although other implementations may.