NAME

mprotect —

control the protection of pages

LIBRARY

Standard C Library (libc, -lc)

SYNOPSIS

#include <sys/mman.h>

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

DESCRIPTION

The mprotect() system call changes the specified pages to have protection prot. Not all implementations will guarantee protection on a page basis; the granularity of protection changes may be as large as an entire region. A region is the virtual address space defined by the start and end addresses of a struct vm_map_entry.

Currently these protection bits are known, which can be combined, OR'd together:

PROT_NONE: No permissions at all.
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 protection flags, FreeBSD provides the ability to set the maximum protection of a region (which prevents mprotect from upgrading the permissions). This is accomplished by or'ing one or more PROT_ values wrapped in the PROT_MAX() macro into the prot argument.

RETURN VALUES

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.

ERRORS

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.

HISTORY

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

The PROT_MAX functionality was introduced in FreeBSD 13.