This is related to the question 'Why do stacks typically grow downwards?', but more from a security point of view. I'm generally referring to x86.

It strikes me as odd that the stack would grow downwards, when buffers are usually written to upwards in memory. For example a typical C++ string has its end at a higher memory address than the beginning.

This means that if there's a buffer overflow you're overwriting further up the call stack, which I understand is a security risk, since it opens the possibility of changing return addresses and local variable contents.

If the stack grew upwards in memory, wouldn't buffer overflows simply run in to dead memory? Would this improve security? If so, why hasn't it been done? What about x64, do those stacks grow upwards and if not why not?