The Linux Kernel Might Drop Memory Protection Extensions Support

Yesterday I wrote about GCC developers moving to drop Intel MPX support and now the Linux kernel developers are looking at dropping the Memory Protection Extensions support too, thereby rendering this modern CPU feature unsupported by Linux.

Memory Protection Extensions is a security feature present since Skylake for checking pointer references at run-time to avoid buffer overflows. MPX support requires plumbing through the kernel, compiler, run-time library, etc. But with Intel not maintaining that support too well on Linux, it looks like it will be dropped entirely. With mainline LLVM Clang not supporting MPX, with GCC dropping it means no compiler support and thus no support for this functionality short of any Intel compiler offering it.

The kernel developers are seeking clarity on Intel's plans for MPX and its maintenance. Well known maintainer Thomas Gleixner is proposing that if indeed the support isn't there, looking at removing it for the Linux 4.18 kernel or if there are chances for it to be revived to temporarily demote it to the kernel staging area until the code can be improved.

Gleixner started the kernel-side discussion about MPX on the mailing list. So far the only response is from fellow kernel developer Ingo Molnar showing MPX test cases appearing broken with the latest kernel.