Yes, mostly, although that's a fairly big undertaking, and any code you have that uses unsafe blocks, or legacy C code (think proprietary drivers), or the like is going to be a weakness. mmap_min_addr is a mitigation measure, by saying, OK maybe we'll dereference NULL sometimes, but we're going to make totally sure that there's nothing mapped there, and certainly nothing that userspace put there. So if we do dereference null, it's just a crash, not execution of userspace-provided code in kernelspace.

And it's the sort of thing that you can turn on in an existing kernel. Rewriting the whole kernel in Rust is a major (but worthwhile) project; adding this restriction is, in its simplest form, just adding `if (addr < 4096) return -EFAULT` to the page-allocation routine. As another commenter pointed out, OS X does have this restriction for 64-bit binaries now.