From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933321AbbDQPxe (ORCPT ); Fri, 17 Apr 2015 11:53:34 -0400 Received: from plane.gmane.org ([80.91.229.3]:35517 "EHLO plane.gmane.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751522AbbDQPxc (ORCPT ); Fri, 17 Apr 2015 11:53:32 -0400 X-Injected-Via-Gmane: http://gmane.org/ To: linux-kernel@vger.kernel.org From: Alex Elsayed Subject: Re: [PATCH 0/3] dm-crypt: Adds support for wiping key when doing suspend/hibernation Date: Fri, 17 Apr 2015 08:53:21 -0700 Message-ID: References: <1428254419-7334-1-git-send-email-pali.rohar@gmail.com> <20150406130045.GA18583@redhat.com> <201504061529.57299@pali> <20150409131208.GA9504@redhat.com> <20150409132836.GD12339@atrey.karlin.mff.cuni.cz> <20150409140842.GA9779@redhat.com> <20150417075211.GC403@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8Bit X-Complaints-To: usenet@ger.gmane.org X-Gmane-NNTP-Posting-Host: 66-87-138-94.pools.spcsdns.net User-Agent: KNode/4.14.6 Cc: dm-devel@redhat.com, linux-raid@vger.kernel.org, linux-pm@vger.kernel.org Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Mike Snitzer wrote: > On Thu, Apr 16 2015 at 5:23am -0400, > Alex Elsayed wrote: > >> Mike Snitzer wrote: >> >> > On Thu, Apr 09 2015 at 9:28am -0400, >> > Pali Rohár wrote: >> > >> >> On Thursday 09 April 2015 09:12:08 Mike Snitzer wrote: >> >> > On Mon, Apr 06 2015 at 9:29am -0400, >> >> > Pali Rohár wrote: >> >> > >> >> > > On Monday 06 April 2015 15:00:46 Mike Snitzer wrote: >> >> > > > On Sun, Apr 05 2015 at 1:20pm -0400, >> >> > > > >> >> > > > Pali Rohár wrote: >> >> > > > > This patch series increase security of suspend and hibernate >> >> > > > > actions. It allows user to safely wipe crypto keys before >> >> > > > > suspend and hibernate actions starts without race >> >> > > > > conditions on userspace process with heavy I/O. >> >> > > > > >> >> > > > > To automatically wipe cryto key for before >> >> > > > > hibernate action call: $ dmsetup message 0 key >> >> > > > > wipe_on_hibernation 1 >> >> > > > > >> >> > > > > To automatically wipe cryto key for before suspend >> >> > > > > action call: $ dmsetup message 0 key >> >> > > > > wipe_on_suspend 1 >> >> > > > > >> >> > > > > (Value 0 after wipe_* string reverts original behaviour - to >> >> > > > > not wipe key) >> >> > > > >> >> > > > Can you elaborate on the attack vector your changes are meant >> >> > > > to protect against? The user already authorized access, why >> >> > > > is it inherently dangerous to _not_ wipe the associated key >> >> > > > across these events? >> >> > > >> >> > > Hi, >> >> > > >> >> > > yes, I will try to explain current problems with cryptsetup >> >> > > luksSuspend command and hibernation. >> >> > > >> >> > > First, sometimes it is needed to put machine into other hands. >> >> > > You can still watch other person what is doing with machine, but >> >> > > once if you let machine unlocked (e.g opened luks disk), she/he >> >> > > can access encrypted data. >> >> > > >> >> > > If you turn off machine, it could be safe, because luks disk >> >> > > devices are locked. But if you enter machine into suspend or >> >> > > hibernate state luks devices are still open. And my patches try >> >> > > to achieve similar security as when machine is off (= no crypto >> >> > > keys in RAM or on swap). >> >> > > >> >> > > When doing hibernate on unencrypted swap it is to prevent leaking >> >> > > crypto keys to hibernate image (which is stored in swap). >> >> > > >> >> > > When doing suspend action it is again to prevent leaking crypto >> >> > > keys. E.g when you suspend laptop and put it off (somebody can >> >> > > remove RAMs and do some cold boot attack). >> >> > > >> >> > > The most common situation is: >> >> > > You have mounted partition from dm-crypt device (e.g. /home/), >> >> > > some userspace processes access it (e.g opened firefox which >> >> > > still reads/writes to cache ~/.firefox/) and you want to drop >> >> > > crypto keys from kernel for some time. >> >> > > >> >> > > For that operation there is command cryptsetup luksSuspend, which >> >> > > suspend dm device and then tell kernel to wipe crypto keys. All >> >> > > I/O operations are then stopped and userspace processes which >> >> > > want to do some those I/O operations are stopped too (until you >> >> > > call cryptsetup luksResume and enter correct key). >> >> > > >> >> > > Now if you want to suspend/hiberate your machine (when some of dm >> >> > > devices are suspeneded and some processes are stopped due to >> >> > > pending I/O) it is not possible. Kernel freeze_processes function >> >> > > will fail because userspace processes are still stopped inside >> >> > > some I/O syscall (read/write, etc,...). >> >> > > >> >> > > My patches fixes this problem and do those operations (suspend dm >> >> > > device, wipe crypto keys, enter suspend/hiberate) in correct >> >> > > order and without race condition. >> >> > > >> >> > > dm device is suspended *after* userspace processes are freezed >> >> > > and after that are crypto keys wiped. And then computer/laptop >> >> > > enters into suspend/hibernate state. >> >> > >> >> > Wouldn't it be better to fix freeze_processes() to be tolerant of >> >> > processes that are hung as a side-effect of their backing storage >> >> > being >> >> > suspended? A hibernate shouldn't fail simply because a user chose >> >> > to suspend a DM device. >> >> > >> >> > Then this entire problem goes away and the key can be wiped from >> >> > userspace (like you said above). >> >> >> >> Still there will be race condition. Before hibernation (and device >> >> poweroff) we should have synced disks and filesystems to prevent data >> >> lose (or other damage) as more as we can. And if there will be some >> >> application which using lot of I/O (e.g normal firefox) then there >> >> always will be race condtion. >> > >> > The DM suspend will take care of flushing any pending I/O. So I don't >> > see where the supposed race is... >> > >> > Anything else that is trapped in userspace memory will be there when >> > the machine resumes. >> > >> >> So proper way is to wipe luks crypto keys *after* userspace processes >> >> are freezed. >> > >> > I know you believe that I'm just not accepting that at face value. >> >> Um, pardon me if I'm being naive, but what about the case of hibernation >> where the swapdev and the root device are both LVs on the same dm_crypt >> device? >> >> The kernel is writing to swap _after_ userspace processes are all frozen; >> that seems to me like an ordering dependency entirely incompatible with >> userspace dropping the key... > > Good point, definitely not compatible with the Pali's approach. > > (but is swap really configured ontop of the same dm-crypt device like > this in practice? I've not heard of that being a common pattern but I > could just be sheltered) Every laptop I've owned in the past five years has been set up as follows: - GPT partition table (mostly for the redundant table at the end in case of fuckups) - 1GB ESP as /boot (first with grub2, then gummiboot) - It's there _anyway_ - 32MB BIOS Boot Partition (for a traditional BIOS bootloader, so I can pop the drive in a non-efi machine if the laptop dies - this has happened) - The rest of the drive is a single dm-crypt volume, with LVM on top. What goes on top of LVM has varied, but these days it's just swap and btrfs. The main reason for this is that I find dealing with crypttab / multiple LUKS devices on boot (or resume from hibernate) to be an incredible hassle; and it's vastly simpler to just have a single dm-crypt device and let Dracut unlock it from a single boot prompt. I haven't set up custom-key secure boot yet, so the evil maid attack is still on the table, but I do this more out of "Eh, why not" (and originally, "I should at least know _how_ to set it up") than actually having stuff I need the security for anyway.