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

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Date:   Tue, 21 Jan 2020 19:08:29 +0100
From:   Jan Kiszka <jan.kiszka@...mens.com>
To:     Ralf Ramsauer <ralf.ramsauer@...-regensburg.de>,
        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

On 18.11.19 14:58, Ralf Ramsauer wrote:
> 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.

I just realized that this thread stranded. Ralf told me that he got no 
access to that reproducer which would be very valuable for us right now 
to validate a static mitigation method in Jailhouse. Any chance to get 
the access?

Thanks a lot,
Jan

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