Linux Adjusts "Meltdown Lite" Mitigation Handling On Newer Zen 5 CPUs

[phoronix]

Phoronix: Linux Fixes "Meltdown Lite" Mitigation Handling On Newer Zen 5 CPUs

Linus Torvalds took to some coding himself today to fix a user-address masking non-canonical speculation issue. The Linux kernel needed an adaptation for this "Meltdown Lite" issue due to different behavior with the latest AMD Zen 5 processors...

https://www.phoronix.com/news/Meltdown-Lite-Zen-5-Linux-Fix

[andyhhp]

The headline is conflating two separate things.

CVE-2020-12965 has been known for ages and affects all AMD CPUs. This is the non-canonical address deference, which Linus described as "Meltdown Lite".

The Zen5 change in behaviour of STAC/CLAC isn't a bug, or a problem really. But it did force us to change the approach for fixing CVE-2020-12965

In fact, the STAC/CLAC change is probably a non-negligible part of why Zen5 is dominating in benchmarks. It will speed up ~all syscalls that ever access guest memory.

[Gamer1227]

Linus doing some coding himself, is like that 50 years old boxing coach, going up and doing a serious fight, quite interesting.

[sophisticles]

I find it hard to believe that AMD CPUs have security vulnerabilities.

Can we get a fact check?

[fitzie]

Wow, Linus booted so many russian kernel developers he has to start coding himself.

[milkylainen]

Linus doing some coding himself, is like that 50 years old boxing coach, going up and doing a serious fight, quite interesting.

Why is that interesting? Like he wouldn't be capable?
I know lots of 50+ that would code circles around their younger peers.

Beside. I credit the man for working his brain, instead of letting it turn to mush.

[archkde]

I find it hard to believe that AMD CPUs have security vulnerabilities.

Can we get a fact check?

Goddammit they even have an advisory for it on their own website, go read it if you don't believe it. Nearly any halfway performant CPU has some transient execution vulnerabilities.

[User29]

Why is that interesting? Like he wouldn't be capable?
I know lots of 50+ that would code circles around their younger peers.

Beside. I credit the man for working his brain, instead of letting it turn to mush.

i think he meant "it's always interesting to see the old masters in action"

[EphemeralEft]

Incoming “I don’t use CPU mitigations anyway, hehehe” comments…

[muncrief]

This is not working because I'm still melting down internally!

Oh wait ...

Never mind