Mapping memory into process address space

I'm trying to launch a new process (without libloader) and I'm having 
trouble mapping memory to it. I've found the prog_attach_ds and 
prog_reserve_utcb_area methods in libloader and ned, but I'm not sure 
where they're getting the memory to assign or the region map for the 
task. Can I just do something like:

L4Re::Util::Cap<L4Re::Dataspace> stack;
L4Re::Env::mem_alloc()->alloc(0x10000, stack);

or are there special steps I need to take when I want to give another 
process access to the same memory?

Thanks!

- Noah Zentzis