Memory Tagging Extension

Arm published the Memory Tagging Extension (MTE) specification in 2019 as a tool for hardware to help find memory corruption bugs. MTE is a memory tagging and tag-checking system, where every memory allocation is tagged with a secret. The hardware guarantees that later requests to access memory are granted only if the request contains the correct secret. If the secrets don’t match, the app crashes, and the event is logged. This allows developers to identify memory corruption bugs immediately as they occur.

https://support.apple.com/guide/security/operating-system-in...

Upon further reading on data only attacks

(https://www.usenix.org/publications/loginonline/data-only-at...)

This makes more sense. You don't trigger MTE since you're not doing anything for force MTE to take action the program isn't actually changing.

My other question would be, why didn't apple use fbounds checking here? They've been doing it aggressively everywhere else.

MTE plus fbounds checking everywhere should lead to an extremly hardened OS

GPU memory/shaders/etc. isn't protected by MTE or PAC. They said "data-only", so I guess GPU commands could fit into this description.

> I'm very curious how the bug survived through MTE

Its not the first time bugs get past MTE, happened with Google Pixel last year ... https://github.blog/security/vulnerability-research/bypassin...