Some near-term arm64 hardening patches

In 2019 BC, robbers would kick down doors to enter houses or rob people at knife point. In 2019 AD, they still do. In 2014, the security on the Nintendo 3DS was broken because the Cube Ninja game didn't bounds check data downloaded from the Net. In 2019, Exim had a remotely exploitable buffer overflow (CVE-2019-16928). There may be fancy new hacks, but people will use whatever works, be it old or new.