Right now, KRF can only target a process based on its `personality(2)` mask. This works really well, but we should support other techniques. Candidate techniques (not exhaustive): * PID (or list of PIDs) * GID (or list of GIDs) * A very early version of KRF did this, and it worked fine. We should re-add it. * Processes that have a given file/file-like object open Since we're operating in user context during a syscall, we should be able to target on anything present in `task_struct`. There's probably additional context we can safely test. Doing this will also give us a nice interface for writing a kernel-independent targeting system, which will help with #8.