The MPX extensions? AMD never supported them, and I've heard rumors that Intel might be dropping support since support never really took off for it. In addition to the meltdown like effects that probably exist, I'd be afraid of the cache effect side channels of just everything needed to load the base and bounds registers.
Not MPX, I think it is called MPK[1]; basically a process can tag each page with a 4 bit identifier (via a kernel provided API) and then, by loading the id on a special register can restrict its own accesses to pages with different keys.
Intel also support memory protection keys. I wonder if they would be enough. Although they might be affected by meltdown like issues.
Does AMD support them?