linux-kernel - Re: [PATCH 4/4] x86,module: Detect CRn and DRn manipulation

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Date:   Wed, 8 Apr 2020 12:50:17 +0200
From:   Jan Kiszka <jan.kiszka@...mens.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Steven Rostedt <rostedt@...dmis.org>, tglx@...utronix.de,
        linux-kernel@...r.kernel.org, hch@...radead.org,
        sean.j.christopherson@...el.com, mingo@...hat.com, bp@...en8.de,
        hpa@...or.com, x86@...nel.org, kenny@...ix.com, jeyu@...nel.org,
        rasmus.villemoes@...vas.dk, pbonzini@...hat.com,
        fenghua.yu@...el.com, xiaoyao.li@...el.com, nadav.amit@...il.com,
        thellstrom@...are.com, tony.luck@...el.com,
        gregkh@...uxfoundation.org, jannh@...gle.com,
        keescook@...omium.org, David.Laight@...lab.com,
        dcovelli@...are.com, mhiramat@...nel.org,
        Wolfgang Mauerer <wolfgang.mauerer@...-regensburg.de>
Subject: Re: [PATCH 4/4] x86,module: Detect CRn and DRn manipulation

On 08.04.20 11:13, Peter Zijlstra wrote:
> On Wed, Apr 08, 2020 at 10:51:38AM +0200, Peter Zijlstra wrote:
>> On Wed, Apr 08, 2020 at 07:58:53AM +0200, Jan Kiszka wrote:
>>> On 07.04.20 23:48, Steven Rostedt wrote:
>>
>>>> Hmm, wont this break jailhouse?
>>
>> Breaking it isn't a problem, it's out of tree and it should be fixable.
>>
>>> Yes, possibly. We load the hypervisor binary via request_firmware into
>>> executable memory and then jump into it. So most of the "suspicious" code is
>>
>> W.T.H. does the firmware loader have the ability to give executable
>> memory? We need to kill that too. /me goes find.
> 
> AFAICT the firmware loader only provides PAGE_KERNEL_RO, so how do you
> get it executable?

memcpy(ioremapped_exec_region, firmware_image)

We only use the loader for getting the blob, not for running it. It has 
to be put at a location that Linux will lose control over anyway.

> 
> I'm thinking the patches Christoph has lined up will take care of this.
> 

It would make sense from a certain POV...

Jan

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