This adds a CONFIG to trigger BUG()s when the kernel encounters unexpected data structure integrity as currently detected with CONFIG_DEBUG_LIST.
Specifically list operations have been a target for widening flaws to gain "write anywhere" primitives for attackers, so this also consolidates the debug checking to avoid code and check duplication (e.g. RCU list debug was missing a check that got added to regular list debug). It also stops manipulations when corruption is detected, since worsening the corruption makes no sense. (Really, everyone should build with CONFIG_DEBUG_LIST since the checks are so inexpensive.) This is mostly a refactoring of similar code from PaX and Grsecurity, along with MSM kernel changes by Stephen Boyd. Along with the patches is a new lkdtm test to validate that setting CONFIG_DEBUG_LIST actually does what is desired. Thanks, -Kees
