linux-kernel - Re: [PATCH 6/6] s390: scrub registers on kernel entry and KVM exit

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Message-Id: <d3950440-d76f-dee4-1e30-9f287dc18fd2@de.ibm.com>
Date:   Fri, 19 Jan 2018 08:57:51 +0100
From:   Christian Borntraeger <borntraeger@...ibm.com>
To:     QingFeng Hao <haoqf@...ux.vnet.ibm.com>,
        Martin Schwidefsky <schwidefsky@...ibm.com>,
        linux-kernel@...r.kernel.org, linux-s390@...r.kernel.org,
        kvm@...r.kernel.org
Cc:     Heiko Carstens <heiko.carstens@...ibm.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Cornelia Huck <cohuck@...hat.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jon Masters <jcm@...hat.com>,
        Marcus Meissner <meissner@...e.de>,
        Jiri Kosina <jkosina@...e.cz>
Subject: Re: [PATCH 6/6] s390: scrub registers on kernel entry and KVM exit



On 01/19/2018 07:29 AM, QingFeng Hao wrote:
> 
> 
> 在 2018/1/17 17:48, Martin Schwidefsky 写道:
>> Clear all user space registers on entry to the kernel and all KVM guest
>> registers on KVM guest exit if the register does not contain either a
>> parameter or a result value.
> I am not sure if I understand this but it will be safer?

It ist similar to commit 0cb5b30698fd ("kvm: vmx: Scrub hardware GPRs at VM-exit").
The idea is to minimize potential payload channels.

> And can we abstract the operations to be a macro like CLEAR_REG_7?

No, please.
xgr %r7,%r7
is absolutely clear what it does, a MACRO often is not.