[$] Indirect branch tracking for Intel CPUs

"Control-flow integrity" (CFI) is a set of technologies intended to preventan attacker from redirecting a program's control flow and taking it over.One of theapproaches taken by CFI is called "indirect branch tracking" (IBT); itspurpose is to prevent an attacker from causing an indirect branch (afunction call via a pointer variable, for example) to go to an unintendedplace. IBT for Intel processors has been under development for some time;after an abrupt turn, support for protecting the kernel with IBT has beenmerged for the upcoming 5.18 release.