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MPROTECT(2) System Calls Manual MPROTECT(2)

mprotect
control the protection of pages

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

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:
Pages may be executed.
Pages may be read.
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.

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.

mprotect() will fail if:
 
 
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The process does not have sufficient access to the underlying memory object to provide the requested protection.
 
 
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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.
 
 
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The accesses requested in the prot argument are not allowed. In particular, PROT_WRITE | mappings are not permitted in most binaries (see kern.wxabort in sysctl(2) for more information).
 
 
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The prot argument is invalid or the specified address range would wrap around.

madvise(2), mincore(2), msync(2), munmap(2)

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

The mprotect() function first appeared in 4.4BSD.

The OpenBSD implementation of mprotect() does not require addr to be page-aligned, although other implementations may.
January 12, 2018 OpenBSD-current