mprotect(2)mprotect(2)NAMEmprotect - Modify access protections of memory mapping
SYNOPSIS
#include <sys/mman.h>
int mprotect(
void *addr,
size_t len,
int prot );
The following definitions of the addr parameter do not conform to cur‐
rent industry standards and are supported only for backward compatibil‐
ity:
caddr_t addr,
const void addr );
STANDARDS
Interfaces documented on this reference page conform to industry stan‐
dards as follows:
mprotect(): XSH4.2, XSH5.0
Refer to the standards(5) reference page for more information about
industry standards and associated tags.
PARAMETERS
Points to the address of the region to be modified. Specifies the
length in bytes of the region to be modified. Specifies access permis‐
sions as PROT_NONE or any combination of PROT_READ, PROT_WRITE, and
PROT_EXEC ORed together.
DESCRIPTION
The mprotect() function modifies the access protection of a mapped file
or shared memory region. The addr and len parameters specify the
address and length in bytes of the region to be modified. The len
parameter must be a multiple of the page size as returned by
sysconf(_SC_PAGE_SIZE). If len is not a multiple of the page size as
returned by sysconf(_SC_PAGE_SIZE), the length of the region will be
rounded up to the next multiple of the page size.
The prot parameter specifies the new access protection for the region.
The <sys/mman.h> header file defines the following access options: The
mapped region can be read. The mapped region can be written. The
mapped region can be executed. The mapped region cannot be accessed.
The prot parameter can be PROT_NONE or any combination of PROT_READ,
PROT_WRITE, and PROT_EXEC ORed together. If PROT_NONE is not specified,
access permissions may be granted to the region in addition to those
explicitly requested, except that write access will not be granted
unless PROT_WRITE is specified.
If the region is a mapped file which was mapped with MAP_SHARED, the
mprotect() function grants read or execute access permission only if
the file descriptor used to map the file is open for reading, and
grants write access permission only if the file descriptor used to map
the file is open for writing. If the region is a mapped file which was
mapped with MAP_PRIVATE, the mprotect() function grants read, write, or
execute access permission only if the file descriptor used to map the
file is open for reading. If the region is a shared memory region which
was mapped with MAP_ANONYMOUS, the mprotect() function grants all
requested access permissions.
The mprotect() function does not modify the access permission of any
region which lies outside of the specified region, except that the
effect on addresses between the end of the region and the end of the
page containing the end of the region is unspecified.
If the mprotect() function fails under a condition other than that
specified by [EINVAL], the access protection of some of the pages in
the range [addr, addr + len) may have been changed. For example, if the
error occurs on some page at addr2, mprotect() may have modified the
protections of all whole pages in the range [addr, addr2).
RETURN VALUES
Upon successful completion, the mprotect() function returns 0 (zero).
Otherwise, mprotect() returns -1 and sets errno to indicate the error.
ERRORS
The mprotect() function sets errno to the specified values for the fol‐
lowing conditions:
The prot parameter specifies a protection that conflicts with the
access permission set for the underlying file. The prot parameter
specifies PROT_WRITE over a MAP_PRIVATE mapping and there are insuffi‐
cient memory resources to reserve for locking the private page. [Tru64
UNIX] Some or all of the addresses in the range starting at addr and
continuing for len bytes are locked. [Tru64 UNIX] The range [addr,
addr + len) includes an invalid address. One of the following condi‐
tions was encountered: The addr parameter is not a multiple of the page
size as returned by sysconf(_SC_PAGE_SIZE). [Tru64 UNIX] The prot
parameter is invalid. [Tru64 UNIX] Addresses in the range [addr, addr
+ len) are invalid for the address space of a process, or they specify
one or more unmapped pages.
SEE ALSO
Functions: getpagesize(2), mmap(2), msync(2), sysconf(3)
Standards: standards(5)mprotect(2)