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

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Message-ID: <60b2a488-74b8-897c-4b25-e228d3fe7d55@oth-regensburg.de>
Date:   Mon, 18 Nov 2019 14:58:14 +0100
From:   Ralf Ramsauer <ralf.ramsauer@...-regensburg.de>
To:     Jan Kiszka <jan.kiszka@...mens.com>,
        Dave Hansen <dave.hansen@...el.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        <linux-kernel@...r.kernel.org>, <kvm@...r.kernel.org>
CC:     "Gupta, Pawan Kumar" <pawan.kumar.gupta@...el.com>
Subject: Re: [FYI PATCH 0/7] Mitigation for CVE-2018-12207

Hi Dave,

On 11/14/19 9:09 AM, Jan Kiszka wrote:
> On 13.11.19 22:24, Dave Hansen wrote:
>> 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.
> 
> Thanks for clarifying this - too bad.
> 
>>
>> 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

I'd appreciate if you could share your code.

>> 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.

Still, it triggers the issue, that's enough to compare it to my reproducer.

>>
> 
> Would be interesting to see this. Ralf and tried something quickly, but
> there seems to be a detail missing or wrong.

Yep, we still can't reproduce the issue on an affected CPU, and don't
know what we miss.

Thanks,
  Ralf

> 
> Jan
>