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.

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.

PROT_CAP

CHERI capabilities may be read or written as dictated by PROT_READ and PROT_WRITE.

PROT_NO_CAP

Respect the absence of PROT_CAP.

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.

For more information on the PROT_CAP and PROT_NO_CAP flags, see the discussion in mmap(2).

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.

[ENOTSUP]

PROT_CAP without PROT_READ or PROT_WRITE.

SEE ALSO

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

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.