friday 27 june 2014
During the past few months, I've been working on bringing Replicant 4.2 support to the Goldelico GTA04, a montherboard replacement for the Openmoko FreeRunner (GTA02) that is manufactured by Golden Delicious with the intent of being free software friendly. The board design is also released under a free licence. There is an active community of developers and users dedicated to the GTA04 and other similar projects, brougt together under the hood of OpenPhoenux. Other similar projects include the upcoming Neo900, a motherboard replacement for the Nokia N900 using similar hardware as the GTA04 and also aiming to be free software friendly, with a particular emphasis on security and privacy features.
I recently published a blog post covering the status of the Replicant 4.2 port to the Goldelico GTA04 on the Replicant blog, with a nice video highlighting which features already work well. However, in the present post, I would like to cover some of the technical aspects of the port, especially regarding the use of a recent mainline Linux kernel with Android 4.2.
Currently, Android devices ship with Linux 3.4, after a long time of using version 3.0, which started with Android 4.0 Ice Cream Sandwich. To this day, the reference common Android kernel repos have branches with Linux 3.10 and experimental work is done on Linux 3.14. That's pretty close to the Linux 3.12 version we're using on the GTA04!
The first challenge to overcome was dealing with suspend and resume. Android uses a particular mechanism to implement opportunistic suspend, using wakelocks: both the kernel and userspace can register these locks to prevent the device from going to suspend. In Android kernels, there is another mechanism that allows some non-critical chips to reach suspend state before the rest of the system: this is earlysuspend. As the whole Android system is built around the concept of wakelocks to handle power management, something similar needed to be implemented in the mainline Linux kernel. After efforts from the Android kernel maintainers, wakelocks were implemented in a clean fashion some time ago. In order to implement opportunistic suspend, a separate interface was implemented on mainline Linux, known as autosleep, which uses different nodes than /sys/power/state (that the Android kernels use directly for opportunistic suspend). Starting in Android 4.1, a library was added to Android in order to detect and handle these different modes.
So thankfully, everything was already in place to use autosleep properly on Android 4.2. Except that it didn't work. This turned out to be because of a dedicated capability that was missing from the Android userspace: CAP_BLOCK_SUSPEND. It turned out to be easier to just revert the patch restricting access to wakelocks to users with that capability in the kernel.
Android USB Gadget and Android Debug Bridge
Android also went their own way in implementing USB device drivers for the various things that are used by Android: mass storage, rndis for USB networking, MTP for file access and a couple others, including ADB. The Android Debug Bridge (ADB) is a great way of debugging what's going on with an Android device, providing easy access to the logs, to a shell and file transfer (these are the features of ADB I use the most). All of that is not integrated at all in the mainline Linux kernel, so there was some substantial work to do here. The first thing to do was importing the related commits from the android-3.10 branch of the common Android Linux kernel. All of that built nicely with only minor code corrections, to follow some API changes in 3.12 and some features like rndis or MTP worked right away, but the most interesting part was left not working: that's the Android Debug Bridge. A few kernel versions back, there used to be a dedicated composite function driver for ADB, but a commit by one of Android's kernel maintainers totally gets rid of it, calling it obsolete with no further information. While attempts to restore it failed, I tried to find out in details why it is obsolete and if that meant the final death of ADB, that I found rather convenient. Thankfully, someone found out what happened and wrote about it: the dedicated ADB driver was being replaced by another one using FunctionFS, a more flexible and generic way of implementing such drivers, directly from userspace. It turns out that FunctionFS support for the userspace ADB server was merged nearly entirely in Android 4.2. I had to backport a missing fix to have it fully working properly and also had to import adaptation a patch in recovery to have sideload working with FunctionFS too. A few bits were also needed in the initialization procedure to have things set up right. Once all of that was done, it could finally run flawlessly!
Headset/headphones detection with SoC Jack
So Jack's a good guy. Everyone knows about that. Whether he's saving the homeland from yet another threat or just letting us know something of interest just got plugged in one hole or another, it always feels great to hear from Jack. However, the Android kernel guys didn't seem to appreciate his participation in the show as much as we all do, or at least until recently.
The traditional way of reporting a headset or headphones plug/unplug in Android kernels was using a switch called h2w, reporting these events to userspace. The mainline kernel prefers another approach, using our beloved Jack SoC architecture. It also provides a convenient way of reporting button pushes, which is quite nice. So instead of rewriting it all using the h2w switch, it struck me that there is a frameworks config option to politely ask Android to give Jack some consideration. And when it does that, everything works great, including button press reports!
saturday 15 march 2014
A few days ago, I disclosed (on behalf of the Replicant projet) our research regarding a back-door found in a proprietary program running on Samsung Galaxy devices' applications processor. This back-door lets the modem perform I/O operations on the device's storage.
For the full statement, please refer to the article posted at Free Software Foundation's website. The relevant technical analysis is available at the Replicant wiki and a complementary statement was issued at the Replicant blog.
In the few hours following the publication, an outstanding number of technology-oriented websites relayed the news, including Phoronix, Slashdot, LWN and XDA-Developers. I'm very glad the press found interest in that research and I'm confident it'll help more and more individuals realize the importance of being in control of their computing: that is, to understand what's at stake with free software.
A few recent developments particularly caught my attention: Ars technica bothered to ask an actual security researcher, Dan Rosenberg his thoughts on our findings. Good thing they decided to go deeper than only duplicating the information. On the other hand, Samsung issued a statement about this issue:
Samsung takes the security of its products extremely seriously. We have investigated the claims that have been made and can confirm that there is no security risk. The Free Software Foundation’s recent allegations are based on a false understanding of the software feature that enables communication between the modem and the Application Processor chipset.
Mostly, the point that is argued by Dan Rosenberg is that there is no evidence of any ability for a remote party to use the back-door, nor any known exploit to make use of it remotely. As a matter of fact, we didn't look at how this could be used over the air: this was not the point of our research. The problem we intended to highlight is not so much about how in practical terms an intruder could use this anti-feature remotely to access and modify the data stored on the device, but rather to show that a particular proprietary software implements a feature that could be used to let the modem gain data I/O access over the device. This is where we find the back-door to be: at the interface between the modem and the applications processor. We do consider the modem to be an “unknown” area that offers no guarantee at all regarding security, since it is running proprietary software. Hence, we believe it is relevant to assume the worse and consider it compromised and subject to remote control. Several indications tend to make us think this is actually what is going on: Craig Murray described how a mobile phone had been remotely converted to a spying device in Murder in Samarkand. Considering the recent revelations regarding the practices of several governments' intelligence agencies, we find it hard to believe there is no way modems cannot be remotely compromised.
The goal of our action was to make people aware of that particular issue. One might consider it to have no value, provided they don't think modems can be remotely compromised and others might see it as a crucial security flaw in the event the modem is compromised, as we do. The fact that it was implemented for another purpose or was not intended to be used in malicious ways doesn't change anything at all: an attacker with remote access to the modem will be able to issue the incriminated requests. There is no possible “false understanding”, in the way Samsung seems to imply here.
For the record, we didn't at any point intend to distort the truth to bring attention to our project or our research, nor did we intend to ruin Samsung's reputation. We simply felt it was our moral responsibility to spread the word about it. I believe anyone can decide for themselves whether they have faith in Samsung's good word that this introduces no further security risk, but let it be clear that it doesn't get any more certain than what good faith can provide. We are still looking forward to working with Samsung to make things right, in case they decide to abandon their current position of denial.
tuesday 11 february 2014
Well, this is mostly going to be about my experience at FOSDEM 2014. Thanks to being a student in a city that features an easy-to-access airport, I was able to attend this year's edition. While my travel schedule was real tight, I only found out the plane was landing not in Brussels, but in Charleroi a few days before departure. Thankfully, it wasn't too late to find another schedule that made it possible for me to arrive at the Friday Beer event around dinner time. The cafe, and the aisle that leads to it were incredibly crowded, to the point that it was barely even possible to make it to the entrance. And once there, despite the fact that the cafe had been reserved for FOSDEM attendees only, I sadly couldn't get in, since the interior of the cafe was apparently full as well. While waiting near the entrance, I was able to see Greg K.H., first of the numerous giants of the free software community I stumbled upon at FOSDEM.
The next day, I was really amazed to see so many people going to FOSDEM, on the way to the event. Public transportation was really filled up with free software hacktivists! Arriving at the ULB campus used for FOSDEM, it really felt spacious and seemed appropriate for an event that big. Lots of interesting discussions took place after the first talk I attended: it was really nice. There were also numerous stands, mostly divided in two buildings, with many interesting people to talk to as well. In the AW building, I enjoyed the Coreboot/Flashrom stand (free software BIOS), Hackable-Devices (apparently focusing on micro-controlers recently), OlinuXino (Allwinner single board computers) and OpenPandora (free software gaming device) with a prototype of the new OMAP5-based version of the device, running apparently really well on GNU/Linux without graphics acceleration blobs. However, the big slice of stands was in the K building, including popular GNU/Linux distros such as Debian or Fedora and desktop environments such as GNOME and KDE. The FSFE was also there, with real good-looking flyers about their Free Your Android campaign, promoting Replicant and F-Droid! I also spent some time at the CaCert booth, and frankly, I was amazed by the depth of the identity verification process. First off, having a single official document to prove of your identity is not enough for these guys, and things get worse when the signature on the ID card (kindly provided by mom at a time I couldn't sign it for myselef) doesn't match the one you produce. Not to mention you have to sign the paper before their eyes, else it's not valid. The ID card itself is also checked to be genuine, with the many UV lights at their disposal and descriptions of the expected results. So I was really surprised how strict the whole process is and I think it's really great that they are taking this very seriously.
On Sunday, we had to rush to get to FOSDEM in time for the F-Droid track by Daniel Martí, followed by an introduction to the linux-sunxi community by Olliver Schinagl, who kindly poked the Replicant project during the talk mentioning that I've been promising Replicant for Allwinner devices for the last six months. Olliver's talk really made me realize what an amazing platform Allwinner is, so I just went ahead and ordered a variety of Allwinner devices to port Replicant to, so we should get there in the near future! On the way to lunch, I quickly saw someone I believe to have been Harald Welte: while I would have loved to have thanked him for his great work, he went by faster than it took me to realize who he was. Time went by, and in the afternoon, I could only attend the Lima talk by Luc Verhaegen before leaving. The project is apparently steadily moving forward, however, without any mind-blowing demo this time. I really had to leave fast after the talk, to catch up with my transportation schedule.
I really have the best memories from FOSDEM, it was really nice and there is no doubt I'll attend next year's edition, hopefully presenting a talk about Replicant there. It was also really nice to see people grateful for the work I'm doing on Replicant. Such huge community gatherings are the best to gather the motivation to keep working on a free software project: actually meeting the community brings a whole different picture compared to what contributing to free software usually feels like individually, hacking alone in my dark room.
wednesday 22 january 2014
Firmwares are programs that do not run on the main processor of a computer: instead, they runs inside separate chips that have a dedicated functionality. Most of the time, firmwares are proprietary programs, which do not respect the user's freedom. When they are not already installed in the chip they run in, the main processor has to load them into the chip, which requires the firmware to be distributed as a file. Since it is proprietary software, I think they shouldn't be shipped with any operating system, not should any operating system ever advise the user to install them.
However, people sometimes need a functionality that depends on proprietary firmwares so bad that they would rather use a system that ships and encourages the use of proprietary software, including the needed firmware, over a free system. In that case, it is better for their freedom that they use a free system with only the proprietary firmware installed, over another system that contains dozens of other proprietary pieces, including ones that also run on the main processor and are able to compromise the whole system (from a security point of view), on top of not respecting the user's freedom.
On Android devices, people are often facing this choice and look around for instructions on how to install only the missing firmwares so that they can avoid installing a system that contains even more proprietary bits. While these instructions cannot be released on free system's official documentation pages, for the sake of not encouraging the use of proprietary software, it makes sense for me to publish such instructions on my personal pages. I have written scripts that extract the firmwares from CyanogenMod installation zips for a few Android devices and push them to the device: cm-firmwares.git
Start by cloning the git repository: cm-firmwares.git (the branch matches the CyanogenMod release version), connect the device via USB, make sure ADB is enabled, allowed and runs as root. Then, bring the CyanogenMod installation zip in the cm-firmwares directory and use the script as follows, for instance for the Galaxy S 3 I9300 (i9300):
Alternatively, it is possible to create a zip containing the firmwares and install it afterwards, using recovery:
./cm-firmwares.sh i9300 zip
monday 09 september 2013
As I'm moving towards studying at the university, I got myself a flat, which makes it perfect for hosting another server, with better capacities and a better Internet connectivity. I was (and still will be for probably about a week) worried of losing mails due to an electric/internet/disk failure on my only server. Thanks to this new opportunity, I'll have good-enough redundancy to stop caring.
My current server is a SheevaPlug, which embeds the kirkwood platform -- not so powerful, but apparently just enough for my needs. The biggest drawback of this device is its lack of connectivity: only one ethernet (not that I really care for more, but it can come in handy), one USB2 port and one sdcard port. Its internal memory is 512Mib NAND and there is no WiFi/bluetooth/audio: just fine for a home server with an external USB disk, but cannot do much more. It is also known to have a PSU over-heating problem (or something of the same sort) that is supposed to make it unusable soon enough. I didn't encounter the issue so far and I've been using it for about 2 or 3 years now. What I'm more concerned about however is the health of the external USB disk. Not that I've seen I/O errors, but it sometimes (maybe once every 4 or 5 months) seems to disconnect, and I have to reboot the plug.
So I decided to go with a DreamPlug for my new place: more connectivity (including e-SATA), more internal storage (on mmc instead of NAND) and a presumably safer PSU. Note that the UART/JTAG module is sold separately, while the SheevaPlug has it embedded. For more details and comparisons between the two devices, I'm maintaining the Plug Computers hardware resource page at LibrePlanet. The device ships with Debian pre-installed, but I prefer to reinstall a sane base and reflash the bootloader. Moreover, the DreamPlug (and the SheevaPlug as well) have full-blown Debian support, with bootable installer images.
Installing Debian Wheezy
Being very happy with the Debian support for both these devices, I started by installing Wheezy on the DreamPlug. Reflashing the bootloader went well: the pre-installed version was
U-Boot 2011.06 (Oct 15 2011 - 02:02:08) and was upgraded to
U-Boot 2012.04.01 (Jun 01 2012 - 02:17:08) which is the version in the wheezy u-boot package. Then I went on to booting the installer uImage and uInitrd (respectively the kernel and initramfs images in u-boot format) from TFTP: I used tftpd which uses the inetd superserver and can be configured from
As the installation went through, it seemed like everything was going perfectly well, except that at some point, the whole thing simply hanged on
Installed u-boot-tools. After some extensive research, it turned out that the problem was caused by the partition layout I chose: ext2 rootfs instead of ext4, which for some reason didn't call the script in charge of updating the
/dev nodes after partitioning the disk. Hence, the nodes in
/dev/disk/by-uuid/ were not updated and the
flash-kernel script couldn't match the (correct) UUID from
fstab. When that happens, the tool (in particular the part that generates the initramfs with the rootfs node) shows an error message and waits for input from stdin, which simply couldn't arrive in the installer context. The workaround I used was to run "udevadm trigger" on the installer shell, kill the script and start that last step again. Then it worked.
As reference, here is the thread on the debian-arm mailing list: Installing Wheezy on DreamPlug: Unable to make the system bootable. I also opened bugs at Debian: flash-kernel: flash_kernel_set_root waits for stdin in a particular case, which makes the installer hang and partman-base: /dev/disk links are not refreshed on dreamplug after repartitioning. Both are not solved yet as of today, but I hope the relevant developers will hop in to make that last remaining annoying bit go away!
In the end, the only thing that still bothers me is the incredibly long boot time. It seems to be because the internal mmc is awfully slow: using an external usb disk reduces the boot time from more than a minute to roughly ten seconds.