From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760846AbbA2CtQ (ORCPT ); Wed, 28 Jan 2015 21:49:16 -0500 Received: from mail-ie0-f177.google.com ([209.85.223.177]:46794 "EHLO mail-ie0-f177.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754377AbbA2CtL (ORCPT ); Wed, 28 Jan 2015 21:49:11 -0500 Message-ID: <54C91C5A.400@android.com> Date: Wed, 28 Jan 2015 09:28:58 -0800 From: Mark Salyzyn User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:31.0) Gecko/20100101 Thunderbird/31.4.0 MIME-Version: 1.0 To: =?UTF-8?B?xYF1a2FzeiBTdGVsbWFjaA==?= CC: linux-kernel@vger.kernel.org, Anton Vorontsov , Colin Cross , Kees Cook , Tony Luck , Krzysztof Kozlowski , =?UTF-8?B?IkJhcnTFgm9taWVqIMW7b8WCbmllcmtpZXdpY3ogc3RsbWFuQHBvY3p0YS5mbSI=?= Subject: Re: [PATCH v4 4/5] pstore: add pmsg References: <1421194580-20230-1-git-send-email-salyzyn@android.com> <871tmfz06r.fsf%stlman@poczta.fm> In-Reply-To: <871tmfz06r.fsf%stlman@poczta.fm> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 01/13/2015 04:16 PM, Łukasz Stelmach wrote: >> A secured user-space accessible pstore object. Writes >> to /dev/pmsg0 are appended to the buffer, on reboot >> the persistent contents are available in >> /sys/fs/pstore/pmsg-ramoops-[ID]. >> >> One possible use is syslogd, or other daemon, can >> write messages, then on reboot provides a means to >> triage user-space activities leading up to a panic >> as a companion to the pstore dmesg or console logs. >> >> Signed-off-by: Mark Salyzyn >> --- > I am not an expert but this smells like duplicating /dev/kmsg. If > I remember correctly since about Linux 3.5 /dev/kmsg is writable for the > user-space and every single process (modulo MAC/DAC) can log there. The > messages from user-space are preserved accross reboots as a part of the > kmsg/printk buffer anyway. > > What is the advantege of pmsg0 over /dev/kmsg? - Precious little user-space content goes to kmsg (otherwise you can ask why is there a syslogd?), there is a reason for this, user space is notorious for containing Personal Identifiable Information whereas kernel information does not. - pmsg0 can take a lot of content (with a ramoops backend) and will not disrupt/DOS the kernel logs. - State, Binary or packetized content can go to /dev/pmsg0 and not interfere with the text content in kmsg - /dev/pmsg0 write is atomic - /dev/pmsg0 is write only, there is no access to the live content _unless_ there is a reboot. - Personal identification which abounds in user space could be placed into /dev/pmsg0, and there is no way except a reboot in order to extract the content, and then /sys/fs/pstore/pmsg-ramoops-0 can be deleted, or heavily MAC and DAC controlled to enforce protection (doing so to kmsg would be unlivable) Sincerely -- Mark Salyzyn