NAME
mimmutable —
control the immutability of
pages
SYNOPSIS
#include
<sys/mman.h>
int
mimmutable(void
*addr, size_t
len);
DESCRIPTION
The
mimmutable()
system call changes currently mapped pages in the region to be marked
immutable, which means their protection or mapping may not be changed in the
future. mmap(2),
mprotect(2), and
munmap(2) to pages marked immutable will return with error
EPERM.
Unmapped pages in the region do not retain immutability, but this behaviour should not be relied upon.
Not all implementations will guarantee that the immutable characteristic can be set on a page basis; the granularity of changes may be as large as an entire region.
RETURN VALUES
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.
ERRORS
The mimmutable() system call will fail
if:
- [
EINVAL] - The virtual address range specified by the addr and len arguments is not valid.
SEE ALSO
HISTORY
The mimmutable() function first appeared
in OpenBSD 7.3.
CAVEATS
At present,
mprotect(2) may reduce permissions on immutable pages marked
PROT_READ | PROT_WRITE to
the less permissive PROT_READ. This one-way
operation is permitted for an introductory period to observe how software
uses this mechanism. It may change to require explicit mutable region
annotation with
__attribute__((section(".openbsd.mutable")))
and explicit calls to mimmutable().