Sequitur Labs did the initial port which besides the actual OP-TEE port also patched U-boot, ARM Trusted Firmware and Linux kernel. Sequitur Labs also pulled together patches for OpenOCD to be able to debug the solution using cheap JTAG debuggers. For more information about the work, please see the press release from June 8 2016.
This port of ARM Trusted Firmware and OP-TEE to Raspberry Pi3
IS NOT SECURE!
Although the Raspberry Pi3 processor provides ARM TrustZone
exception states, the mechanisms and hardware required to
implement secure boot, memory, peripherals or other secure
functions are not available. Use of OP-TEE or TrustZone capabilities
within this package _does not result_ in a secure implementation.
This package is provided solely for educational purposes.
This is a working setup, but there are quite a few patches that are put on top of forks and some of the patches has been put together by just pulling files instead of (correctly) cherry-pick patches from various projects. For some of the projects it could take some time to get the work accepted upstream. Due to this, things might not initially be on official git's and in some cases things will be kept on a separate branch. But as time goes by we will gradually move it over to the official gits. We are fully aware that this is not the optimal way to do this, but we also know that there is a strong interest among developers, students, researches to start work and learn more about TEE's using a Raspberry Pi. So instead of delaying this, we have decided to make what we have available right away. Hopefully there will be some enthusiast that will help out making proper upstream patches sooner or later.
| Project | Base fork | What to do |
|---|---|---|
| linux | https://github.com/Electron752/linux.git commit: b48d47a32b2f27f55904e7248dbe5f8ff434db0a | Three things here. 1. The base is a fork itself and should be upstreamed. 2. Apply patch arm64: dt: RPI3: Add optee node 3. We have cherry picked the patches from LSK OP-TEE 4.4 |
| arm-trusted-firmware | https://github.com/96boards-hikey/arm-trusted-firmware commit: bdec62eeb8f3153a4647770e08aafd56a0bcd42b | This should instead be based on the official OP-TEE fork or even better the official ARM repository. The patch itself should also be upstreamed. |
| U-boot | https://github.com:linaro-swg/u-boot.git | This is just a mirror of the official U-boot git. The patches should be upstreamed. |
| OpenOCD | https://github.com/seqlabs/openocd | The patches should be upstreamed. |
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First thing to pay attention to the OP-TEE prerequisites. If you forget that, then you can get all sorts of strange errors.
-
Follow the generic build instructions from the README.md file in this git. Note that the initial build will download a couple of files, like the official Raspberry Pi 3 firmware, the overlay root fs etc. However, that is only done once, so subsequent builds won't re-download them again (as long as you don't delete them).
-
The last step is to partition and format the memory card and to put the files onto the same. That is something we don't want to automate, since if anything goes wrong, in worst case it might wipe one of your regular hard disks. Instead what we have done, is that we have created another makefile target that will tell you exactly what to do. Run that command and follow the instructions there.
$ make img-help- Boot up the Pi. With all files on the memory card, put the memory card into the Raspberry Pi 3 and boot up the system. On the UART (for wiring, see section 6) you will see the system booting up. When you have a shell, then it's simply just to follow the xtest instructions to load tee-supplicant and run xtest.
We encourage anyone interested in getting this into a better shape to help out. We have identified a couple issues while working with this. Some are harder to solve than others.
Currently we are using a cpio archive with busybox as a base, that works fine and has a rather small footprint it terms of size. However in some cases it's convenient to use something that reminds of what is used in distros. For example having the ability to use a package manager like apt-get, pacman or rpm (dnf) to make it easy to add new applications and developer tools.
Suggestions to look into regarding creating a better rootfs
- Create a setup where one use buildroot instead of manually creating the cpio archive.
- Create a 64bit Raspbian image. This would be the ultimate goal. Besides just the big work with building a 64bit Raspian image, one would also need to ensure that Linux kernel gets updated accordingly (i.e., pull 64bit RPi3 patches and OP-TEE patches into the official Raspbian Linux kernel build).
Having that said, in the section below about NFS boot, we've been successfully using an Ubuntu based root-fs (linaro-vivid).
Booting via NFS and TFTP is quite useful for several reasons, but the obvious reason when working with Raspberry Pi is that you don't have to move the SD-card back and forth between the host machine and the RPi itself. Below we will describe how to setup both the TFTP part and the NFS part so we have both ways covered. We will get kernel, optee.bin and the device tree blob from the tftpd server and we will get the root fs from the NFS server. Note that this guide doesn't focus on any desktop security, so eventually you would need to harden your setup. Another thing is that this seems like a lot of steps, and it is, but most of them is something you do once and never more and it will save tons of time in the long run.
Note also, that this particular guide is written for the ARMv8-A setup using OP-TEE. But, it should work on plain RPi also if you change U-boot and filesystem accordingly.
In the description below we will use the following terminology:
HOST_IP=192.168.1.100 <--- This is your desktop computer
RPI_IP=192.168.1.200 <--- This is the Raspberry Pi
There are several different servers to use, but in the description we're going
to use atftpd, so start by apt-get that package.
$ sudo apt-get install atftpdNext edit the configuration file for atftpd
$ sudo vim /etc/default/atftpdAnd change the file so it looks exactly like this, nothing less, nothing more!
USE_INETD=false
OPTIONS="--tftpd-timeout 300 --retry-timeout 5 --mcast-port 1758 --mcast-addr 239.239.239.0-255 --mcast-ttl 1 --maxthread 100 --verbose=5 /tftpboot"
Create the tftpboot folder and change the permissions
$ sudo mkdir /tftpboot
$ sudo chmod -R 777 /tftpboot
$ sudo chown -R nobody /tftpbootAnd finally restart the daemon
$ sudo /etc/init.d/atftpd restartStart by installing the NFS server
$ sudo apt-get install nfs-kernel-serverThen edit the exports file,
$ sudo vim /etc/exportsIn this file you shall tell where your files/folder are and the IP's allowed to access the files. The way it's written below will make it available to every machine on the same subnet (again, be careful about security here). Let's add this line to the file (it's the only line necessary in the file, but if you have several different filesystems available, then you should of course add them too).
/srv/nfs/rpi 192.168.1.0/24(rw,sync,no_root_squash,no_subtree_check)
Next create the folder
$ sudo mkdir /srv/nfs/rpiAfter this, restart the nfs kernel server
$ service nfs-kernel-server restartWe need to prepare and put the files on the tftpd and the NFS-server. There are several ways to do it, copy files, symlink etc.
We're just going to create symlinks. By doing so you don't have to think about
copy files, just rebuild and you have the latest version available for the next
boot. On my computer I've symlinked like this (in my /tftpboot folder):
$ ll
lrwxrwxrwx 1 jbech jbech 65 jul 14 09:03 Image -> /home/jbech/devel/optee_projects/rpi3/linux/arch/arm64/boot/Image
lrwxrwxrwx 1 jbech jbech 85 jul 14 09:03 optee.bin -> /home/jbech/devel/optee_projects/rpi3/arm-trusted-firmware/build/rpi3/debug/optee.bin
lrwxrwxrwx 1 jbech jbech 90 Sep 13 11:19 bcm2710-rpi-3-b.dtb -> /home/jbech/devel/optee_projects/rpi3/linux/arch/arm64/boot/dts/broadcom/bcm2710-rpi-3-b.dtb
We are now going to put the root fs on the location we prepared in the previous
section (5.2). The path to the filesystem.cpio.gz will differ on your machine,
so update accordingly.
$ cd /srv/nfs/rpi
$ sudo gunzip -cd /home/jbech/devel/optee_projects/rpi3/build/../gen_rootfs/filesystem.cpio.gz | sudo cpio -idmv
$ sudo rm -rf /srv/nfs/rpi/boot/*There are two ways to update uboot.env. First, you can edit
build/rpi3/firmware/uboot.env.txt file, which is used as simple text source for
generation of uboot.env during build and you can just edit u-boot env via UART
and save new values to uboot.env. By using the second way you can avoid rebuilding
and copying uboot.env to SD card.
All you need to do is to edit network configuration in build/rpi3/firmware/uboot.env.txt.
You have to change value of serverip to the IP address of your NFS/TFTP server,
gatewayip to your router IP address and nfspath to the exported path, where root FS
is stored (/srv/nfs/rpi). Then you need to generate new uboot.env:
$ cd /home/jbech/devel/optee_projects/rpi3/boot/
# clean previous uboot.env
$ make u-boot-env-clean
# generate new
$ make u-boot-jtag-binThen you need to copy your newly generated uboot.env(it's stored in ../out/uboot.env)
to the BOOT partition of your SD card.
Start by inserting the UART cable and open up /dev/ttyUSB0
# sudo apt-get install picocom
$ picocom -b 115200 /dev/ttyUSB0Power up the Raspberry Pi and almost immediately hit any key and you should see
the U-Boot> prompt. First edit your NFS/TFTP server IP address:
U-Boot> setenv serverip '192.168.1.100'
Perform the same steps for gateway(your router IP address) and
nfspath (the exported path, where root FS is stored, for example /srv/nfs/rpi)
If you want those environment variables to persist between boots, then type.
U-Boot> saveenv
And don't worry about the FAT: Misaligned buffer address ... message, it will
still work.
With all preparations done correctly above, you should now be able to boot up the device and kernel, secure side OP-TEE and the entire root fs should be loaded from the network shares. Power up the Raspberry, halt in U-Boot and then type.
U-Boot> run nfsboot
Profit!
If everything works, you can simply copy paste files like xtest, the trusted
applications etc, directly from your build folder to the /srv/nfs/rpi folders
after rebuilding them. By doing so you don't have to reboot the device when
doing development and testing. Note that you cannot make symlinks to those like
we did with Image, bcm2710-rpi-3-b.dtb and optee.bin.
The default root filesystem used for OP-TEE development is a simple CPIO archive
used as initramfs. That is small and is good enough for testing and debugging.
But sometimes you want to use a more traditional Linux filesystem, such as those
that are in distros. With such filesystem you can apt-get (if Debian based)
other useful tools, such as gdb on the device, valgrind etc to mention a few. An
example of such a rootfs is the linaro-vivid-developer-20151215-114.tar.gz,
which is an Ubuntu 15.04 based filesystem. The procedure to use that filesystem
with NFS is the same as for the CPIO based, you need to extract the files to a
folder which is known by the NFS server (use regular tar -xvf ... command).
Then you need to copy xtest and tee-supplicant to <NFS>/bin/, copy
libtee.so* to <NFS>/lib/ and copy all *.ta files to
<NFS>/lib/optee_armtz/. Easiest here is to write a small shell script or add a
target to the makefile which will do this so the files always are up-to-date
after a rebuild.
When that has been done, you can run OP-TEE tests, TA's etc and if you're only updating files in normal world (the ones just mentioned), then you don't even need to reboot the RPi after a rebuild.
First a word of warning here, even though this seems to be working quite good as of now, it should be well understood that this is based on incomplete and out of tree patches. So what are the major changes that enables this? First OpenOCD currently doesn't contain ARMv8-A / AArch64 support in the upstream tree. A couple of different people have put something together that gets the job done. But to get in a shape for upstream, there is still quite a lot left to do. The other change needed is in U-Boot, that is where we configure the RPi3 GPIO pins so that they will talk JTAG. The pin configuration and the wiring for the cable looks like this:
| JTAG pin | Signal | GPIO | Mode | Header pin |
|---|---|---|---|---|
| 1 | 3v3 | N/A | N/A | 1 |
| 3 | nTRST | GPIO22 | ALT4 | 15 |
| 5 | TDI | GPIO4 | ALT5 | 7 |
| 7 | TMS | GPIO27 | ALT4 | 13 |
| 9 | TCK | GPIO25 | ALT4 | 22 |
| 11 | RTCK | GPIO23 | ALT4 | 16 |
| 13 | TDO | GPIO24 | ALT4 | 18 |
| 18 | GND | N/A | N/A | 14 |
| 20 | GND | N/A | N/A | 20 |
Note that this configuration seems to remain in the Raspberry Pi3 setup we're using. But someone with root access could change the GPIO configuration at any point in time and thereby disable JTAG functionality.
We have created our own cables, get a standard 20-pin JTAG connector and 22-pin connector for the RPi3 itself, then using a ribbon cable, connect the cables according to the table in section 6 (JTAG pin <-> Header pin). In addition to that we have also connected a USB FTDI to UART cable to a few more pins.
| UART pin | Signal | GPIO | Mode | Header pin |
|---|---|---|---|---|
| Black (GND) | GND | N/A | N/A | 6 |
| White (RXD) | TXD | GPIO14 | ALT0 | 8 |
| Green (TXD) | RXD | GPIO15 | ALT0 | 10 |
We are using the Sequitur Labs OpenOCD fork, simply clone that to your computer and then building is like a lot of other software, i.e.,
$ ./bootstrap
$ ./configure
$ makeWe leave it up to the reader of this guide to decide if he wants to install it
properly (make install) or if he will just run it from the tree directly. The
rest of this guide will just run it from the tree.
In the OpenOCD fork you will find the necessary RPi3 OpenOCD config. As you can read there, it's prepared for four targets, but only one is enabled. The reason for that is simply because it's a lot simpler to get started with JTAG when running on a single core. When you have a stable setup using a single core, then you can start playing with enabling additional cores.
...
target create $_TARGETNAME_0 aarch64 -chain-position $_CHIPNAME.dap -dbgbase 0x80010000 -ctibase 0x80018000
#target create $_TARGETNAME_1 aarch64 -chain-position $_CHIPNAME.dap -dbgbase 0x80012000 -ctibase 0x80019000
#target create $_TARGETNAME_2 aarch64 -chain-position $_CHIPNAME.dap -dbgbase 0x80014000 -ctibase 0x8001a000
#target create $_TARGETNAME_3 aarch64 -chain-position $_CHIPNAME.dap -dbgbase 0x80016000 -ctibase 0x8001b000
...
Depending on the JTAG debugger you are using you'll need to find and use the interface file for that particular debugger. We've been using J-Link debuggers and Bus Blaster successfully. To start an OpenOCD session using a J-Link device you type:
$ cd <openocd>
$ ./src/openocd -f ./tcl/interface/jlink.cfg -f ./pi3.cfgTo be able to write commands to OpenOCD, you simply open up another shell and type:
$ nc localhost 4444From there you can set breakpoints, examine memory etc ("> help" will give you
a list of available commands).
The pi3.cfg file is configured to listen to GDB connections on port 3333. So all you have to do in GDB after starting OpenOCD is to connect to the target on that port, i.e.,
# Ensure that you have gdb in your $PATH
$ aarch64-linux-gnu-gdb -q
(gdb) target remote localhost:3333To load symbols you just use the symbol-file <path/to/my.elf as usual. For
convenience you can create an alias in the ~/.gdbinit file. For TEE core
debugging this works:
define jlink_rpi3
target remote localhost:3333
symbol-file /home/jbech/devel/optee_projects/rpi3/optee_os/out/arm/core/tee.elf
end
So, when running GDB, you simply type: (gdb) jlink_rpi3 and it will both
connect and load the symbols for TEE core. For Linux kernel and other binaries
you would do the same.
If you have everything prepared, i.e. a working setup for Raspberry Pi3 and OP-TEE. You've setup both OpenOCD and GDB according to the instructions, then you should be good to go. Start by booting up to U-Boot, but stop there. In there start by disable SMP and then continue the boot sequence.
U-Boot> setenv smp off
U-Boot> boot
When Linux is up and running, start a new shell where you run OpenOCD:
$ cd <openocd>
$ ./src/openocd -f ./tcl/interface/jlink.cfg -f ./pi3.cfgStart a third shell, where you run GDB
$ aarch64-linux-gnu-gdb -q
(gdb) target remote localhost:3333
(gdb) symbol-file /home/jbech/devel/optee_projects/rpi3/optee_os/out/arm/core/tee.elf
Next, try to set a breakpoint, here use hardware breakpoints!
(gdb) hb tee_ta_invoke_command
Hardware assisted breakpoint 1 at 0x842bf98: file core/kernel/tee_ta_manager.c, line 534.
(gdb) c
Continuing.
And if you run tee-supplicant and xtest for example, the breakpoint should trigger and you will see something like this in the GDB window:
Breakpoint 1, tee_ta_invoke_command (err=0x84940d4 <stack_thread+7764>,
err@entry=0x8494104 <stack_thread+7812>, sess=sess@entry=0x847bf20, clnt_id=clnt_id@entry=0x0,
cancel_req_to=cancel_req_to@entry=0xffffffff, cmd=0x2,
param=param@entry=0x84940d8 <stack_thread+7768>) at core/kernel/tee_ta_manager.c:534
534 {
From here you can debug using normal GDB commands.
As mentioned in the beginning, this is based on forks and etc, so it's a moving targets. Sometime you will see that you loose the connection between GDB and OpenOCD. If that happens, simply reconnect to the target. Another thing that you will notice is that if you're running all on a single core, then Linux kernel will be a bit upset when continue running after triggering a breakpoint in secure world (rcu starving messages etc). If you have suggestion and or improvements, as usual, feel free to contribute.