linux-kernel - Re: [PATCH] KVM: X86: Allow userspace to define the microcode version

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Message-ID: <CANRm+CzODxLQ4UHgFCnpjABmBUvi9sbw=uyO1xk1dyWgnH86ig@mail.gmail.com>
Date:   Mon, 26 Feb 2018 18:06:42 +0800
From:   Wanpeng Li <kernellwp@...il.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     LKML <linux-kernel@...r.kernel.org>, kvm <kvm@...r.kernel.org>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Radim Krčmář <rkrcmar@...hat.com>
Subject: Re: [PATCH] KVM: X86: Allow userspace to define the microcode version

2018-02-26 17:41 GMT+08:00 Borislav Petkov <bp@...en8.de>:
> On Mon, Feb 26, 2018 at 03:23:58PM +0800, Wanpeng Li wrote:
>> From: Wanpeng Li <wanpengli@...cent.com>
>>
>> Linux (among the others) has checks to make sure that certain features
>> aren't enabled on a certain family/model/stepping if the microcode version
>> isn't greater than or equal to a known good version.
>>
>> By exposing the real microcode version, we're preventing buggy guests that
>
> Where do we prevent userspace from coming up with some non-sensical
> microcode revision?

I think it is the host admin(e.g. cloud provider)'s responsibility to
set an expected microcode revision. In addition, the non-sensical
value which is written by the guest will not reflect to guest-visible
microcode revision and just be ignored in this implementation.

Regards,
Wanpeng Li