I don't understand much from MTE/Android or MIE/iOS but the explanation is also confusing when:

- They claim Apple did a great job integrating MIE in iOS - iOS doesn't encourage to opt into MTE ... Apple's docs warn developers of performance and stability issues

So it seems like even for iOS, this special security feature is only available for Apple own iOS app (at most?).

Then also:

> Even Signal doesn't opt-in. Our approach enables forcing using MTE in the standard allocators regardless.

So does that mean that Signal and any other apps are enrolled in MTE on Graphene?

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?