FPGAd

FPGAd is a WIP rust project. It provides a strictly confined snap which will provide a mechanism to dynamically load and unload bitstreams to FPGA devices on Ubuntu Core. It mitigates the need for other snaps containing bitstreams to have super privileges. Instead, those other snaps will connect to FPGAd and FPGAd will have the necessary privileges. This is for several reasons, but mostly to:

1. make the snap store team happy (not publishing lots of super privileged snaps).
2. add a place for checking and verifying bitstreams before loading them for additional safety/security.
3. make it easier to port already existing bitstream packages to snap store.

In order to understand why the super privileges are necessary, you must understand that loading a bitstream fundamentally changes the FPGA device's behaviour including what the connections to the CPU are/do. To do this, device tree of the system must be changed (overlaid). This device tree tells Ubuntu a lot of information about the device, such as how much ram the system has. It should be clear to see, then, that compromising the device tree is very powerful.

Key considerations

fw_search_path:

The kernel system only works with relative paths and searches relative to provided fw_search_path and hardcoded firmware locations see the kernel docs for details. When loading an overlay, only the relative path of the loaded overlay file is retrievable. If there is a file with the same name in the default search paths (such as /lib/firmware), there is no guarantee that the loaded file is the one provided by the user since the system will successfully load from there even in the event that the file is not present at the provided path. It is up to the user to verify that the correct overlay is applied, such as by checking that the appropriate drivers are loaded.

Anticipated Architecture

Building and running from source

From a fresh install, you must install build-essential, rustup (includes cargo) and pull the source from the repo then build. To run locally you must configure the dbus daemon. Our docs assume the use of systemd.

install rust

Following the rust documentation, installing rust can be done by running

curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh

and following the instructions in the installer. For FPGAd, no custom settings are required if building on the target device, so the standard installation option is fine.

install build dependencies

The rust compiler has some dependencies (like gcc, make and libc-dev) so please install these. For debian distros, this can be done in one go by installing build-essential (sudo may be necessary):

apt update && apt install -y build-essential

build

cargo makes this simple:

cargo build --workspace 

will build all parts including cli.

cargo build --bin fpgad

will build fpgad and any direct dependencies in debug mode (no optimisations, no stripping of the binary etc.). Release mode can be used by running

cargo build --release [opts] 

run

Using default build settings, the resulting binaries will be in ./target/debug/ such as ./target/debug/fpgad for the daemon and ./target/debug/cli for the command line application. If using release, then the directory is ./target/release/.

If running as a standalone binary (not snap) then dbus needs to be configured to know about fpgad. If using systemd then an example configuration is provided in ./daemon/tests/test_data/com.canonical.fpgad.conf and can be installed by running

sudo cp ./daemon/tests/test_data/com.canonical.fpgad.conf /etc/dbus-1/system.d/com.canonical.fpgad.conf
sudo systemctl reload dbus

but please note that this configuration is not intended for general use since it allows dbus clients to access privileged IO operations on files. To mitigate this, adjust the file as necessary, e.g. change

<!-- Unprivileged interface -->
<policy context="default">
    ...
    <allow send_interface="com.canonical.fpgad.control"/>
</policy>

to

<!-- Unprivileged interface -->
<policy context="default">
    ...
    <deny send_interface="com.canonical.fpgad.control"/>
</policy>

to block unprivileged use of the control interface.

fpgad itself requires privileges to access certain system files so run it as sudo (or, better yet, configured it as a systemd daemon)

sudo RUST_LOG=trace ./target/<mode>/fpgad