Re: [FYI PATCH 0/7] Mitigation for CVE-2018-12207

[Dave Hansen]

On 11/13/19 12:23 AM, Paolo Bonzini wrote:
> On 13/11/19 07:38, Jan Kiszka wrote:
>> When reading MCE, error code 0150h, ie. SRAR, I was wondering if that
>> couldn't simply be handled by the host. But I suppose the symptom of
>> that erratum is not "just" regular recoverable MCE, rather
>> sometimes/always an unrecoverable CPU state, despite the error code, right?
> The erratum documentation talks explicitly about hanging the system, but
> it's not clear if it's just a result of the OS mishandling the MCE, or
> something worse.  So I don't know. :(  Pawan, do you?

It's "something worse".

I built a kernel module reproducer for this a long time ago.  The
symptom I observed was the whole system hanging hard, requiring me to go
hit the power button.  The MCE software machinery was not involved at
all from what I could tell.

About creating a unit test, I'd be personally happy to share my
reproducer, but I built it before this issue was root-caused.  There are
actually quite a few underlying variants and a good unit test would make
sure to exercise all of them.  My reproducer probably only exercised a
single case.