Date:   Wed, 22 Feb 2023 23:25:02 +0100
From:   Borislav Petkov <bp@alien8.de>
To:     Tavis Ormandy <taviso@gmail.com>
Cc:     Andrew Cooper <andrew.cooper3@citrix.com>,
        linux-kernel@vger.kernel.org, x86@kernel.org
Subject: Re: x86: AMD Zen2 ymm registers rolling back
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On Wed, Feb 22, 2023 at 01:26:37PM -0800, Tavis Ormandy wrote:
> Thanks - confirmed, it *doesn't* repro with 0x8301055, but does repro
> with 0x830104d.

Good.

> Annoyingly, I thought I was using the most recent microcode, but it seems
> like there is some bug and debian wasn't applying it at boot.

Well, actually, microcode loading is so simple - you don't absolutely
need to rely on the distros to do it for ya.

You simply get it from

git://git.kernel.org/pub/scm/linux/kernel/git/firmware/linux-firmware.git

and copy all the bin files from amd-ucode/ into /lib/firmware/amd-ucode/

Technically, you'd need only the one for your family but the tools can
deal with multiple files in there.

And then you're all set - dracut or whatever creates your initrd will
add it. You can even add it by hand, see

Documentation/x86/microcode.rst

> That seems like a scary errata :-/

Yeah, modern x86 hardware is crazy complex. And we've had worse. :-\

-- 
Regards/Gruss,
    Boris.

https://people.kernel.org/tglx/notes-about-netiquette