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by dinckelman 1061 days ago
So as far as I understand, if I have the latest AMD microcode on my system, at least on Linux, I don't really have to worry about this anymore?

As a sidenote, any word on Microsoft working on this?

3 comments

If you're not running a Zen 2 CPU or APU, you don't have to worry about this.

If you're running the latest kernel, which automatically sets the chicken bit, you don't have to worry about this.

If you're running fixed microcode, which is only available for Rome, Castle Peak and Mendocino, you don't have to worry about this. Good microcode revisions are:

    Rome / Castle Peak: 0x0830107a (published)
    Xbox Series X: unknown
    Renoir / Grey Hawk: 0x0860010b
    Lucienne: 0x08608105
    Matisse: 0x08701032
    Van Gogh (Steam Deck): unknown
    Mendocino: 0x08a00008  (published) 


If you're running neither the latest kernel, nor fixed microcode, you should set the chicken bit yourself until you have updated those.

    wrmsr -a 0xc0011029 $(($(rdmsr -c 0xc0011029) | (1<<9)))
You can run the PoC if you want to check: https://github.com/google/security-research/tree/master/pocs...
Microsoft is dead silent on zenbleed.

It's not easy to set chicken bit manually either.

In other words windows on AMD Zen2 is fcked.