Now that arenas are implemented, the core design for github.com/GrapheneOS/har is fully implemented. Fine-grained randomization for slabs still needs to be completed, but it hasn't been a priority because it isn't incredibly valuable and it's hard to evaluate different approaches.
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You can see from the issue tracker that other than nearly all of the planned work is on API extensions, tuning the size classes and optimization:
github.com/GrapheneOS/har
Memory tagging for ARMv8.5 will be a major feature but that's obviously on hold until hardware is available.
