Editing Self-modifying code (section)

==Security issues==
Because of the security implications of self-modifying code, all of the major [[operating system]]s are careful to remove such vulnerabilities as they become known. The concern is typically not that programs will intentionally modify themselves, but that they could be maliciously changed by an [[exploit (computer security)|exploit]].

One mechanism for preventing malicious code modification is an operating system feature called [[W^X]] (for "write [[xor]] execute").  This mechanism prohibits a program from making any page of memory both writable and executable. Some systems prevent a writable page from ever being changed to be executable, even if write permission is removed.{{citation needed|date=May 2022}} Other systems provide a '[[backdoor (computing)|back door]]' of sorts, allowing multiple mappings of a page of memory to have different permissions. A relatively portable way to bypass W^X is to create a file with all permissions, then map the file into memory twice. On Linux, one may use an undocumented SysV shared memory flag to get executable shared memory without needing to create a file.{{Citation needed|date=August 2018}}