linux-kernel - Re: [PATCH v5 01/13] taint: Introduce a new taint flag (insecure)

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Message-ID: <3B92973A-A2D2-4FCB-A2A2-030057229D4B@zytor.com>
Date:   Tue, 05 Feb 2019 15:07:42 -0800
From:   hpa@...or.com
To:     Randy Dunlap <rdunlap@...radead.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Andy Lutomirski <luto@...nel.org>
CC:     "Chang S. Bae" <chang.seok.bae@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...nel.org>,
        Andi Kleen <ak@...ux.intel.com>,
        Markus T Metzger <markus.t.metzger@...el.com>,
        Ravi Shankar <ravi.v.shankar@...el.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 01/13] taint: Introduce a new taint flag (insecure)

On February 5, 2019 2:46:11 PM PST, Randy Dunlap <rdunlap@...radead.org> wrote:
>On 2/5/19 1:21 PM, Andrew Morton wrote:
>> On Fri, 1 Feb 2019 18:42:29 -0800 Andy Lutomirski <luto@...nel.org>
>wrote:
>> 
>>> On Fri, Feb 1, 2019 at 12:54 PM Chang S. Bae
><chang.seok.bae@...el.com> wrote:
>>>>
>>>> For testing (or root-only) purposes, the new flag will serve to tag
>the
>>>> kernel taint accurately.
>>>>
>>>> When adding a new feature support, patches need to be incrementally
>>>> applied and tested with temporal parameters. Currently, there is no
>flag
>>>> for this usage.
>>>
>>> I think this should be reviewed by someone like akpm.  akpm, for
>>> background, this is part of an x86 patch series.  If only part of
>the
>>> series is applied, the kernel will be blatantly insecure (but still
>>> functional and useful for testing and bisection), and this taint
>flag
>>> will be set if this kernel is booted.  With the whole series
>applied,
>>> there are no users of the taint flag in the kernel.
>>>
>>> Do you think this is a good idea?
>> 
>> What does "temporal parameters" mean?  A complete description of this
>> testing process would help.
>> 
>> I sounds a bit strange.  You mean it assumes that people will
>partially
>> apply the series to test its functionality?  That would be
>inconvenient.
>
>Ack.  I don't think we need to (or should) worry about that kind of
>muckup.
>
>> - Can the new and now-unused taint flag be removed again at
>>   end-of-series?
>> 
>> - It would be a lot more convenient if we had some means of testing
>>   after the whole series is applied, on a permanent basis - some
>>   debugfs flag, perhaps?
>> 

I would like to see this taint flag, though, because sometimes it is useful to write test modules (e.g. when I was testing SMAP) which are dangerous even if out of tree.

In case of an escape or pilot error gets it into the wrong kernel, it is a very good thing to have the kernel flagged.
-- 
Sent from my Android device with K-9 Mail. Please excuse my brevity.