Re: RFC: userspace exception fixups

[Dave Hansen]

On 11/8/18 12:05 PM, Andy Lutomirski wrote:
> Hmm.  The idea being that the SDK preserves RBP but not RSP.  That's
> not the most terrible thing in the world.  But could the SDK live with
> something more like my suggestion where the vDSO supplies a normal
> function that takes a struct containing registers that are visible to
> the enclave?  This would make it extremely awkward for the enclave to
> use the untrusted stack per se, but it would make it quite easy (I
> think) for the untrusted part of the SDK to allocate some extra memory
> and just tell the enclave that *that* memory is the stack.

I really think the enclave should keep its grubby mitts off the
untrusted stack.  There are lots of ways to get memory, even with
stack-like semantics, that don't involve mucking with the stack itself.

I have not heard a good, hard argument for why there is an absolute
*need* to store things on the actual untrusted stack.

We could quite easily have the untrusted code just promise to allocate a
stack-sized virtual area (even derived from the stack rlimit size) and
pass that into the enclave for parameter use.