What's this about?
This digest got it wrong on 2026-08-31. That day's entry reported, from a GrapheneOS post, that the Pixel 11 no longer supports hardware memory tagging. GrapheneOS has now said the Pixel 11 does have MTE support after all. The hardware is present; it is currently disabled, which is what produced the original reading — the shipped firmware did not enable it, so from outside it looked absent.
What is MTE, restated?
Arm's Memory Tagging Extension. Every 16-byte chunk of memory gets a 4-bit tag, and four otherwise-unused high bits of each pointer carry a tag too. Access memory with a pointer whose tag does not match and the hardware faults. Your allocator gives adjacent allocations different tags, so an overflow into the neighbour is caught immediately rather than silently corrupting it. It is hardware-accelerated AddressSanitizer, and it turns the most-exploited bug class — use-after-free and buffer overflow — into an immediate crash.
What's the community saying?
- The clarification thread had to clarify itself: one commenter's "it was disabled" was corrected to "the hardware is there, it is currently disabled" — the confusion was contagious.
- Why disabled? The most-supported explanation is the performance cost, and a claim that it was to save money is challenged as unevidenced.
- The more practical reason, from someone who has run it: MTE causes apps, services and occasionally the kernel to throw MTE SIGSEGV, which becomes a serious problem when the developers of those apps do not care enough to fix them.
- My 08-31 entry drew a general lesson — "hardware mitigations are a vendor product decision and can be withdrawn." That lesson still holds, but the specific fact it rested on was wrong.