Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752924AbdCNUlz (ORCPT ); Tue, 14 Mar 2017 16:41:55 -0400 Received: from smtp.math.uni-bielefeld.de ([129.70.45.10]:37600 "EHLO smtp.math.uni-bielefeld.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751028AbdCNUlx (ORCPT ); Tue, 14 Mar 2017 16:41:53 -0400 Subject: Re: [PATCH] drm/exynos: Print kernel pointers in a restricted form To: Krzysztof Kozlowski , Tobias Jakobi Cc: Inki Dae , Joonyoung Shim , Seung-Woo Kim , Kyungmin Park , David Airlie , Kukjin Kim , Javier Martinez Canillas , dri-devel@lists.freedesktop.org, linux-arm-kernel@lists.infradead.org, linux-samsung-soc@vger.kernel.org, linux-kernel@vger.kernel.org References: <20170314183804.13788-1-krzk@kernel.org> <20170314190859.y55wlc4z7xdsbbxg@kozik-lap> <20170314195240.gj7jbgql7hfziw42@kozik-lap> From: Tobias Jakobi Message-ID: Date: Tue, 14 Mar 2017 21:41:50 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:49.0) Gecko/20100101 Firefox/49.0 SeaMonkey/2.46 MIME-Version: 1.0 In-Reply-To: <20170314195240.gj7jbgql7hfziw42@kozik-lap> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1854 Lines: 49 Krzysztof Kozlowski wrote: > On Tue, Mar 14, 2017 at 08:17:35PM +0100, Tobias Jakobi wrote: >> 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. > > The %pK will not help for dmesg or /proc/kmsg but it will help for > console (/dev/ttySACN, ttySN etc) because effectively it uses the same > vsprintf()/pointer() functions. Thanks for the explanation, I didn't know that there was a difference there. In that case, looks good to me. > As I said, we could argue whether securing console is worth... usually > attacker having access to it has also physical access to the machine so > everything gets easier... Still, putting %pK there certainly doesn't hurt. - Tobias > > Best regards, > Krzysztof > > -- > To unsubscribe from this list: send the line "unsubscribe linux-samsung-soc" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html >