OpenBSD's kernel gets W^X treatment on amd64

brynet writes: Theo de Raadt wrote:

Over the last two months Mike Larkin (mlarkin@) modified the amd64 kernel to follow the W^X principles. It started as a humble exercise to fix the .rodata segment, and kind of went crazy. As a result, no part of the kernel address space is writeable and executable simultaneously. At least that is the idea, modulo mistakes. Final attention to detail (which some of you experienced in buggy drafts in snapshots) was to make the MP and ACPI trampolines follow W^X, furthermore they are unmapped when not required. Final picture is many architectures were improved, but amd64 and sparc64 look the best due to MMU features available to service the W^X model. The entire safety model is also improved by a limited form of kernel ASLR (the code segment does not move around yet, but data and page table ASLR is fairly good.