Reply To: Security

The following was from James Babcock and sent to me directly; repeated here for wider comment:
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In the security talk, you said that the Mill will not generally have
high-granularity entries in its PLB, for performance reasons, but I
don’t think you said anything either way about the TLB. Will the Mill
support fine-slicing of address spaces in the TLB? If so, how much do
slices cost, and if not would it be feasible to add? I ask mainly
because a finely-sliced address space in the TLB, combined with some
memory-allocator tricks, could solve the use-after-free security
problem, which Mill has not yet proposed a solution for.

The essence of the fix is separating reuse-of-address-space from
reuse-of-memory, and not reusing the address space of freed objects
for as long as possible. If it were cheap to reclaim memory without
having to reuse associated address space, for objects sized and
aligned to >=32 bytes but smaller than a traditional 4kb page, then
the use-after-free problem would be pretty much solved.