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Man Pages
MPROTECT(2) FreeBSD System Calls Manual MPROTECT(2)

mprotect
control the protection of pages

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. 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:

No permissions at all.
The pages can be read.
The pages can be written.
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.

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

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

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.

February 26, 2020 FreeBSD 13.1-RELEASE

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