linux-kernel - Re: [PATCH] drm/exynos: Print kernel pointers in a restricted form

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Message-ID: <de5e8583-748b-9df2-f7cc-c1b4fb499d17@math.uni-bielefeld.de>
Date:   Tue, 14 Mar 2017 20:17:35 +0100
From:   Tobias Jakobi <tjakobi@...h.uni-bielefeld.de>
To:     Krzysztof Kozlowski <krzk@...nel.org>,
        Tobias Jakobi <tjakobi@...h.uni-bielefeld.de>
Cc:     Inki Dae <inki.dae@...sung.com>,
        Joonyoung Shim <jy0922.shim@...sung.com>,
        Seung-Woo Kim <sw0312.kim@...sung.com>,
        Kyungmin Park <kyungmin.park@...sung.com>,
        David Airlie <airlied@...ux.ie>, Kukjin Kim <kgene@...nel.org>,
        Javier Martinez Canillas <javier@....samsung.com>,
        dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/exynos: Print kernel pointers in a restricted form

Krzysztof Kozlowski wrote:
> On Tue, Mar 14, 2017 at 08:01:41PM +0100, Tobias Jakobi wrote:
>> Hello Krzysztof,
>>
>> I was wondering about the benefit of this. From a quick look these are
>> all messages that end up in the kernel log / dmesg.
>>
>> IIRC %pK does nothing there, since dmest_restrict is supposed to be used
>> to deny an unpriviliged user the access to the kernel log.
>>
>> Or am I missing something here?
> 
> These are regular printks so depending on kernel options (e.g. dynamic
> debug, drm.debug) these might be printed also in the console. Of course
> we could argue then if access to one of the consoles is worth
> securing.
This here suggests otherwise.
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/sysctl/kernel.txt#n388

I have not tested this, but IIRC %pK is not honored by the kernel
logging infrastucture. That's why dmesg_restrict is there.

Correct me if I'm wrong.

- Tobias


> Actually, I think that we should get rid of printing of these kernel
> pointers entirely...
> 
> 
> Best regards,
> Krzysztof
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