Facebook shipped buggy stack overflow detection in the Hermes JavaScript engine used by React Native:
https://github.com/facebook/hermes/issues/1535
It breaks when the default stack guard is 64k instead of 4k. The standard 64-bit ARM Linux ABI requires 64k. So far only 1 person noticed a broken app.
We're going to be temporarily reverting our change in today's release before Facebook's broken code reaches more apps. We tried lying to apps about the stack layout to hide this change but that breaks compatibility much more. We'll have to detect the Facebook library instead.
Not particularly important since we weren't planning on switching to standard 64k stack probes instead of 4k stack probes to avoid risk. However, it's nicer if it's larger to cover 3rd party code without stack probes. Very minor compared to other things blocked by app compat.
The main feature that's blocked due to third party app bugs is enabling hardware memory tagging by default for all user installed apps. That works fine but catches many memory corruption bugs. We might put the toggle into the setup wizard so that most users end up enabling it.
We want to disable the 32-bit ARM system call ABI in the kernel config on devices without 32-bit app support. Certain widespread anti-tampering frameworks use it even on devices like the Pixel 8 without CPU level support for 32-bit. We'll have to extend the seccomp filters.
Enabling ShadowCallStack for Vanadium worked well but caused issues with WebView-based apps, likely due to anti-tampering code. This would be nice even on the recent devices with PAC and MTE until we have stack allocation MTE enabled... which is blocked due to app bugs for now.