Manual Pages  — MPROTECT

mprotect – control the protection of pages

LIBRARY SYNOPSIS DESCRIPTION RETURN VALUES ERRORS SEE ALSO HISTORY

Standard C Library (libc, -lc)

#include <sys/mman.h>

int
mprotect(void *addr, size_t len, int prot);

The mprotect() system call changes the specified pages to have protection prot.

The prot argument shall be PROT_NONE (no permissions at all) or the bitwise or of one or more of the following values:

PROT_READ	The pages can be read.
PROT_WRITE
	The pages can be written.
PROT_EXEC	The pages can be executed.

In addition to these standard protection flags, the FreeBSD implementation of mprotect() provides the ability to set the maximum protection of a region (which prevents mprotect from adding to the permissions later). This is accomplished by bitwise or'ing one or more PROT_ values wrapped in the PROT_MAX() macro into the prot argument.

The mprotect function returns the value 0 if successful; otherwise the value -1 is returned and the global variable errno is set to indicate the error.

The mprotect() system call will fail if:

[EACCES]
	The calling process was not allowed to change the protection to the value specified by the prot argument.
[EINVAL]
	The virtual address range specified by the addr and len arguments is not valid.
[EINVAL]
	The prot argument contains unhandled bits.
[ENOTSUP]
	The prot argument contains permissions which are not a subset of the specified maximum permissions.

The mprotect() system call was first documented in BSD 4.2 and first appeared in BSD 4.4 .

The PROT_MAX functionality was introduced in FreeBSD 13 .