Comment by perarneng

Google likely cut MTE to reduce the die space required by CPU cache. It saves them money on a feature they never deployed by default and only used for a few processes as part of Android Advanced Protection Mode (AAPM) without enabling it in the Linux kernel. Their security team should have gotten it deployed by default for a large portion of the OS by now and then it would have been much harder to justify removing it. The small performance impact of asymmetric mode is irrelevant for the vast majority of the OS and it can also be used in the near zero cost asynchronous mode. We use synchronous in the kernel for security reasons but they didn't have to do that.

It's a completely different story for GrapheneOS where it means losing one of the main kernel and userspace security protections. This is one of the only ways we can significantly harden the Linux kernel with existing security features. The Linux kernel has always been a huge security liability for Android and AI models are making that much more obvious to everyone.

Google will likely end up heavily using MTE in the future. Pixel 11 devices won't be able to benefit from it. They're at the start of 7 years of updates but they won't be getting the benefit of future updates enabling MTE. Pixel 8 and later will benefit from Google likely expanding use of MTE for AAPM and eventually beginning to use it by default. It's unlikely Google will stop working on expanding MTE due to the Pixel 11 hardware decision. Multiple other OEMs are interested in MTE for devices made for businesses and governments even if Google decided it wasn't worth the cost for Pixels.

iOS uses MTE for nearly all of the important parts of the OS. It uses MTE within the kernel and for a substantial portion of the base OS processes. They focused on deploying it to the most security relevant processes first but it's deployed for a large portion of the OS beyond those. Apple has done a very good job protecting the OS with it. They've done a very poor job getting the app ecosystem to adopt it.

Android has more app ecosystem adoption than iOS due to having a better open source app ecosystem where GrapheneOS users have asked apps to enable it by default. Many GrapheneOS users are also force enabling MTE for user installed apps via our recommended toggle for it. Those users are reporting invalid memory access to developers via our dedicated notification system for invalid memory accesses it catches. For Android app developers, not opting into MTE doesn't mean their app won't be used with MTE due to GrapheneOS.

GrapheneOS uses MTE for the kernel and nearly every userspace process including all the base OS apps. We've had to fix many upstream Linux kernel and Pixel kernel driver bugs found by MTE. However, we aren't trying to fix the Pixel userspace drivers code ourselves so we have a few userspace processes excluded from MTE caused by userspace driver library/service bugs.

We recommend users enable our toggle for enabling MTE by default for every user installed app not explicitly marked as incompatible in our compatibility database. GrapheneOS has user-facing notifications for invalid memory accesses caught by MTE providing a traceback to share with the app developers. Users can use the per-app toggle to work around it if it makes an app unusable. We take the same approach for other aggressive exploit protections provided by GrapheneOS. Exploit protections with only rare compatibility issues are enabled by default for apps with a per-app toggle to opt-out and no toggle for the global default.

I see a significant difference between making a security feature available but opt-in during a teething phase, and removing the feature altogether. Am I missing something?

I think they mean "this is a terrible development" in the sense that this is terrible news/turn of events. They arent criticizing GrapheneOSs software development.