linux-kernel - Re: [PATCH v2] KVM: x86: do not read FS/GS base MSRs when saving them

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Message-ID: <f4671e9f-7d7b-8328-b9c0-ba85a97e8dce@redhat.com>
Date:   Thu, 4 Jan 2018 02:17:06 +0100
From:   Paolo Bonzini <pbonzini@...hat.com>
To:     Andy Lutomirski <luto@...capital.net>
Cc:     Andy Lutomirski <luto@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        kvm list <kvm@...r.kernel.org>
Subject: Re: [PATCH v2] KVM: x86: do not read FS/GS base MSRs when saving them

On 04/01/2018 01:16, Andy Lutomirski wrote:
>> Note that the value I'm storing in HOST_FS_BASE and HOST_GS_BASE is
>> only used if FS/GS selector is zero.  If FS/GS selector is not
>> zero, it is not used.  Does that avoid this issue?
>> 
> I'm not convinced that this is correct.  It's not obviously a
> security problem in the context of KVM, but a lot of state can leak
> this way.
> 
> My general preference would be to make the code obviously fully
> reload the host state.

I'll try to write a v3 that looks more obviously correct.

Paolo