ARM Memory Tagging: how it improves C/C++ memory safety (2018) [pdf]
18 comments
·October 25, 2025javierhonduco
abalone
Not only does M5 have MTE, it has an "enhanced" version of it.
"We conducted a deep evaluation and research process to determine whether MTE, as designed, would meet our goals for hardware-assisted memory safety. Our analysis found that, when employed as a real-time defensive measure, the original Arm MTE release exhibited weaknesses that were unacceptable to us, and we worked with Arm to address these shortcomings in the new Enhanced Memory Tagging Extension (EMTE) specification, released in 2022."[1]
The enhancements add:[2]
* Canonical tag checking
* Reporting of all non-address bits on a fault
* Store-only Tag checking
* Memory tagging with Address tagging disabled
[1] https://security.apple.com/blog/memory-integrity-enforcement...
[2] https://developer.arm.com/documentation/109697/0100/Feature-...
summa_tech
It's MTE4. The "enhancements" mostly make it easier for Apple developers to hack XNU into continuing to operate with MTE.
astrange
It's more like MTE was originally intended as a debugging tool (like ASan), and MTE4 makes it work as a security hardening measure.
commandersaki
Do you know if macos has the changes needed to make use of MIE with M5? I assume that it has with iPadOS.
musicale
Compiler/runtime support via clang and llvm should help I hope.
I'd like to get to the point where web browsers (for example) always run with memory-safe compilation and runtime features on every platform. OS kernels would be nice as well.
It will be nice to see more OSes ship with memory safety on by default for everything. Maybe OpenBSD is next?
throwawaymaths
sel4 ships with memory safety on by default.
tempaccount420
Sooo, less reasons (more excuses) for people to move from C++ to Rust?
dagmx
If you don’t mind moving the whole issue to runtime, then sure. The value of rust is that you catch these issues at compile time so you’re not releasing these sorts of bugs in the first place and aren’t reliant on the capabilities of the users machine to catch it for you.
1718627440
Honestly it feels at the right abstraction layer too. With Rust you rely on correctness in translation, it is much better to have defense in depth than in breadth.
kibwen
Rust is already part of defense-in-depth. Despite its memory safety, Rust still turns on ASLR, guard pages, stack probes, etc.
qwertyuiop_
Intel / AMD bringing this to x86 soon.
https://community.intel.com/t5/Blogs/Tech-Innovation/open-in...
e-dant
It disappoints me to see hardware compensate for the failures of software. We should have done better.
a-dub
wouldn't it be like a crime against the crown to not have a cheri like thing in arm?
commandersaki
I always see cheri brought up and admittedly I know very little about it, except that the ergonomics appear poor requiring twice the storage for each pointer and ground up rearchitecting of the OS, making it quite unappealing from an engineering standpoint.
wahern
FreeBSD, kernel and base, was ported to CHERI, along with PostgreSQL.
> We have adapted a complete C, C++, and assembly-language software stack, including the opensource FreeBSD OS (nearly 800 UNIX programs and more than 200 libraries including OpenSSH, OpenSSL, and bsnmpd) and PostgreSQL database, to employ ubiquitous capability-based pointer and virtual-address protection.
Most programs didn't require any changes at all. Even most pointer-integer-pointer conversions can be automatically handled by the toolchain and runtime. See https://www.cl.cam.ac.uk/research/security/ctsrd/pdfs/201904...
I am incredibly happy that Apple has added MTE support to the latest iPhones and perhaps the M5 chips as well (?). If that’s the case I don’t think any other personal computers have anything close to Apple machines in terms of memory safety and related topics (Secure Enclave etc).
Hope other vendors will ship MTE in their laptop and desktop chips soon enough. While I’m very positive about x86_64 adding support for this (ChkTag), it’ll definitely take a while…
In my opinion a worthwhile enough reason to upgrade but feels like a waste given my current devices work great.