linux-kernel - Re: [PATCH] x86: also disable FSRM if ERMS is disabled

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Message-ID: <Yy3yJfz213Lqo4KC@zn.tnic>
Date:   Fri, 23 Sep 2022 19:51:33 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Daniel Verkamp <dverkamp@...omium.org>
Cc:     x86@...nel.org, linux-kernel@...r.kernel.org,
        Tony Luck <tony.luck@...el.com>
Subject: Re: [PATCH] x86: also disable FSRM if ERMS is disabled

On Fri, Sep 23, 2022 at 10:25:05AM -0700, Daniel Verkamp wrote:
> Yes, we hit this in crosvm when booting the guest kernel with either
> OVMF or u-boot on an Intel 12th Gen CPU. The guest kernel boots fine
> when loaded directly (using the crosvm kernel loader and not running
> any firmware setup in the guest), but it crashes when booting with
> firmware inside the first forward memmove() after alternatives are set
> up (which happens to be in printk). I haven't gotten to the bottom of
> why exactly using firmware is causing this to be set up in an
> inconsistent way, but this is a real-world situation, not just a
> hypothetical.

Sounds like broken virt firmware or so. And if that is not an issue on
baremetal, then the virt stack should be fixed - not the kernel.

> Now that I look at it with fresh eyes again, maybe we should instead
> directly patch the memmove FSRM alternative so that the flag-set
> version just does the same jmp as the ERMS one. I can prepare a patch
> for that instead of (or in addition to) this one if that sounds
> better.

So, if the virt firmware deviates from how the real hardware behaves,
then the kernel needs no fixing.

So you'd have to figure out why is the virt firmware causing this and
not baremetal.

Then we can talk about fixes.

Thx.

-- 
Regards/Gruss,
    Boris.

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