We have a partial port of GrapheneOS to the Pixel 11 series after a week of work on it. We're unable to complete the port due to lack of support for ARM hardware memory tagging in software, firmware and near certainly hardware. It appears Google cut an important security feature to save money.
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ARM hardware memory tagging (MTE) is used by GrapheneOS across the entire base OS including the kernel and every standard base OS process. It's only temporarily disabled for a few device-specific processes. It greatly improves protection against nearly all remote exploits and many local exploits.
Pixel 8 launched with hardware MTE support in October 2023. We integrated it into our hardened_malloc project and began using it across the OS later that month. Android and the Pixel OS never started using it by default. Android Advanced Protection Mode in Android 16 enables it for a few processes.
Apple's Memory Integrity Enforcement (MIE) is an always enabled feature on the iPhone 17. It's simply a high quality implementation of MTE using the latest standard extensions. It uses MTE in the most secure mode in the kernel and a large portion of userbase. They did a very good job integrating it.
Apple's MIE and Android 16+ AAPM don't use MTE for user installed apps unless those explicitly opt in. GrapheneOS enables it for more apps automatically and has a toggle for users to opt-in for every user installed app. There's a per-app toggle to opt-out for incompatible apps which is uncommon.
Neither iOS or Android encourage app developers to opt into MTE and other more aggressive security features used in the base OS. Apple's docs warn developers of performance and stability issues. Even Signal doesn't opt-in. Our approach enables forcing using MTE in the standard allocators regardless.
Pixel 11 does have security improvements including moving to post-quantum secure verified boot (ML-DSA) and replacing Samsung Shannon IMS with AOSP IMS. Titan M3 should significantly improve protection against data extraction in Before First Unlock state. It's too bad they ruined it by cutting MTE.
