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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:

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

Upon successful completion, the value 0 is returned; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

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), mimmutable(2), msync(2), munmap(2)

STANDARDS

The mprotect() function conforms to IEEE Std 1003.1-2008 (“POSIX.1”).

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.