cervus

A WebAssembly subsystem for Linux.

What is it?

Cervus implements a WebAssembly "usermode" on top of the Linux kernel (which tries to follow the CommonWA specification), enabling wasm applications to run directly in ring 0, while still ensuring safety and security.

But why?

• Managed execution (making it possible to perform optimizations based on tracing/partial evaluation)
• Avoid performance overhead introduced by system calls & address space switches
• Zero-copy I/O is possible

Things that are working and not working

Working:

• An interpreter based on HexagonE
• Binary translation & loading based on wasm-core
• Most of CommonWA ("everything is a URL", file I/O, command-line arguments)
• IPC (only broadcast supported by now, with URL prefix ipc-broadcast://)

Not working:

• Floating point
• JIT
• Everything else

Build

Kernel module

Requirements:

• xargo
• latest nightly rust
• kernel headers
• gnu make & gcc

./build_all.sh
sudo insmod glue/cervus.ko

Loader (cvctl)

This installs the cvload and cvrun binaries:

cd cvctl
cargo install

Applications

Cervus implements most of CommonWA (tracked at #2), whose examples can be found at cwa-rs/examples.

For example, to build and run the cat example:

sudo chmod 666 /dev/cvctl
cd cwa-rs
cargo build --target wasm32-unknown-unknown --release --example cat
cvrun target/wasm32-unknown-unknown/release/examples/cat.wasm file:///etc/lsb-release

To launch an IPC broadcast sender and then read from it:

cargo build --target wasm32-unknown-unknown --release --example broadcast_sender
cvrun target/wasm32-unknown-unknown/release/examples/broadcast_sender.wasm your_broadcast

(in another terminal)

cvrun target/wasm32-unknown-unknown/release/examples/cat.wasm ipc-broadcast://your_broadcast | dd of=/dev/null bs=4K

Contribute

I'm busy with my College Entrance Examination until ~June 10, 2018, before which I cannot actively maintain this project. However, there are a few things that can be relatively easily worked on:

• A JIT based on Cretonne

Since Cretonne supports no_std, this should be relatively easy compared to other JIT approaches.

Interface with the rest of the system by implementing the Backend trait, for which the interpreter-based backend located in src/backend/hexagon_e is a good example to start with.

• Network API

Blocking network APIs can be added as virtual system calls.

License

Cervus itself has to use the GPL 2.0 license because it links to the Linux kernel. However, user code that runs on Cervus is not limited by this.