Linux 5.9 To Bring Arm Memory Tagging Extension Support

[pierce]

Pretty keen to see this trickle down into the dotnet core GC some day.

Hardware accelerated garbage collection? Yes please!

[raster]

All this is great. But do we have actually seen any live ARM - based motherboard - and what advantage it brings? (I would love to test these out and replace my server using these if it makes sense)

Think of this as "hardware valgrind/ASAN". If you don't know what these are... ummm... think of it as the ability to detect buffer overflows or invalid accesses and either log or trap like a segfault but not at 4k page sized chunks but at 16 byte sized chunks. That means the hardware can literally detect going past the end of an array or allocation allocated on the stack or by malloc or in a global in great detail. If all "memory objects" (allocated chunks e.g. malloc) then it'll detect going beyond one and into another (well due to the memory tagging its not 100% detected. It's a 1 in 16 chance of getting past any check at any point, but it means you are literally running a hardware debugger realtime without the massive overheads of things like ASAN and even worse - valgrind and you can run this all the time all day long on everything for a very low cost. This means bugs will get found and weeded out as they are always being looked for. Even if one check is luckily gotten past, then the next one probably won't. an attacker won't get far at all before hitting a MTE trap.

It's not a security mechanism as such that will make you totally safe - it doesn't guarantee it, but it reduces attack vectors but most of all it allows millions of systems to be running all their workloads all day long with real usage patterns and then bugs eventually will be trapped, backtraces logged and shared... and this will ultimately lead to fixes and better quality software. Like Linus says - given enough eyeballs all bugs are shallow. Given enough hardware running MTE, all bugs will eventually be trapped, logged, fixed and vanish. Then we all win.

[Smurphy]

All this is great. But do we have actually seen any live ARM - based motherboard - and what advantage it brings? (I would love to test these out and replace my server using these if it makes sense)

[jabl]

Isn't Memory segmentation supposed to do this?

Segmentation prevents a process from accessing the memory of another process. MTE is more fine grained, it's targeted at individual allocations within a single process. MTE allows catching (at least some) buffer overflow and use-after-free type errors which are common in memory-unsafe languages like C or C++.

How would this prevent the vulnerabilities from meltdown, spectre and the like?

It has nothing to do with these vulnerabilities.

[pracedru]

Isn't Memory segmentation supposed to do this?
How would this prevent the vulnerabilities from meltdown, spectre and the like?

[phoronix]

Phoronix: Linux 5.9 To Bring Arm Memory Tagging Extension Support

The 64-bit ARM code building up for the Linux 5.9 cycle is set to mainline Memory Tagging Extension (MTE) support as another security improvement inbound...

http://www.phoronix.com/scan.php?page=news_item&px=Linux-5.8-Arm-Memory-Tagging