KLab

NOTE: This software is still in the early stages of development. If you are confused, find some bugs, or just want some help, please file an issue or come talk to us at https://dapphub.chat/channel/k-framework.

Klab is a tool for generating and debugging K-framework reachability proofs, tailored for formal verification of ethereum smart contracts.

It uses a custom, compact format for expressing the behavior of an ethereum contract, from which it generates K framework reachability rules. The klab server invokes the K framework prover while storing intermediate proof steps, allowing the proof object to be explored in an interactive way.

KLab uses a client-server architecture, meaning that you'll need to have both a KLab server and a KLab client running. The server will recieve proof requests and dispatch them to K frameworks proving tool, while the client builds and explores proofs. Ask at https://dapphub.chat/channel/k-framework for access to a KLab server if you do not want to setup your own.

Setting up KLab Server and Client

One option is to use Docker:

docker run -it dapphub/klab

See below for details on using Docker.

Dependencies

Installing klab automatically installs K and KEVM. You will therefore need the dependencies of K.

To install all of these dependencies on Ubuntu, try:

sudo apt-get install make gcc maven openjdk-8-jdk flex pkg-config libmpfr-dev autoconf libtool pandoc zlib1g-dev z3 libz3-dev npm

On ArchLinux:

sudo pacman -S  base-devel rsync opam pandoc jre8-openjdk mpfr maven z3 nodejs npm

On OSX, using Homebrew, after installing the command line tools package:

brew tap homebrew/cask-versions
brew cask install caskroom/versions/java8
brew install automake libtool gmp mpfr pkg-config pandoc maven opam z3 node

Installing

Clone the repo and install the latest stable version v0.2.3 with

git clone --branch v0.2.3 https://github.com/dapphub/klab.git
cd klab
make deps

To make klab available from the terminal, you can either just export the path to the klab executable in bin/, or use:

make link

This installs symlinks globally at /usr/local/bin and /usr/local/libexec (will require sudo on Linux machines). You can also specify a custom directory for installation by doing:

PREFIX=/path/to/custom/prefix make link

OPTIONAL: klab has some optional Haskell components, for which the recommended installation method is nix. If you have nix, you can install the Haskell components with

make deps-haskell

Environment Setup

The file env will setup the environment for you if sourced from the root directory of the repo.

source env

It sets three environment variables:

• PATH: include the klab executable.
• KLAB_EVMS_PATH: the EVM semantics to use.

OPTIONAL: If you want to use a different version of K than what the KEVM ships with, you can set:

• KLAB_K_PATH: override implementation of K.

Building proofs

The KLab client is run in a proof directory, and will request that the KLab server execute the proof. Proof claims are expressed in a custom, succint specification language, from which K reachability rules are generated using klab build. In order to generate reachability claims, you need to provide a .sol.json generated from the contract you want to verify. With solc installed, you can generate this file by running

solc --combined-json=abi,bin,bin-runtime,srcmap,srcmap-runtime,ast <path-to-contract> > <path-to-output>

You need to tell klab where to find the sol.json file by specifying it under the implementations header in your projects config.json. Consult the examples for more information. With your config pointing to the outputted evm binaries, you can run klab build in the same direcory:

cd examples/SafeAdd
klab build

This will generate a fail and success reachability rule for each act of your specification in the SafeAdd/out/specs directory.

Running proofs

To prove the specifications generated by klab build, run klab prove. If you want to explore this proof later with the GUI, you will need to pass a --dump flag.

klab prove --dump out/specs/SafeAdd_add_pass_rough.k

Once the proof is complete, you can explore the generated symbolic execution trace using:

klab debug $(klab hash out/specs/SafeAdd_add_pass_rough.k

Key Bindings

Toggle different views by pressing any of the following keys:

View Commands:

• t - display the (somewhat) pretty K term.
• c - display current constraints.
• k - display <k> cell.
• b - display behavior tree.
• s - diaplay source code.
• e - display evm specific module.
• m - display memory cell.
• d - display debug cells (see toggling debug cells below).
• r - display applied K rule.
• z - display z3 feedback from attempted rule application.
• Up/Dn - scroll view up and down.

Navigation Commands:

• n - step to next opcode
• p - step to previous opcode
• Shift+n - step to next k term
• Shift+p - step to previous k term
• Ctrl+n - step to next branch point
• Ctrl+p - step to previous branch point

Toggling Debug Cells:

The following commands are prefixed with : (and are typed at the bottom of the interface). It's possible to toggle the debug cells view for specific cells, which prints out the JSON representation of the given cells. Remember, you must turn on the debug cells view to see these (above).

• :show ethereum.evm.callState.gas - show the contents of the <gas> cell in the debug cells view.
• :hide ethereum.evm.callStack.pc - hide the contents of the <pc> cell in the debug cells view.
• :omit gas pc - omit the contents of the <gas> and <pc> cells in the term view.
• :unomit pc programBytes - unomit the contents of the <pc> and <programBytes> cells in the term view.

Troubleshooting

Outdated npm

You might have problems due to an outdated npm, in that case try updating it with:

npm install npm@latest -g
npm install -g n
n stable

KLab server requesting files at incorrect directory

What it looks like:

$ klab server

18.07.30 14-46-50: exec dfc688db4cc98b5de315bdfaa2512b84d14c3aaf3e58581ae728247097ff300d/run.sh
18.07.30 14-47-32: out Debugg: dfc688db4cc98b5de315bdfaa2512b84d14c3aaf3e58581ae728247097ff300d

fs.js:119
throw err;
^

Error: ENOENT: no such file or directory, open '/tmp/klab/b042c99687ae5018744dc96107032b291e4a91f1ab38a6286b2aff9a78056665/abstract-semantics.k'
at Object.openSync (fs.js:443:3)
at Object.readFileSync (fs.js:348:35)
at getFileExcerpt (/home/dev/src/klab/lib/rule.js:5:4)
at Object.parseRule (/home/dev/src/klab/lib/rule.js:21:16)
at Object.getblob (/home/dev/src/klab/lib/driver/dbDriver.js:49:19)
at Object.next (/home/dev/src/klab/lib/driver/dbDriver.js:113:56)
at Stream._n (/home/dev/src/klab/node_modules/xstream/index.js:797:18)
at /home/dev/src/klab/node_modules/@cycle/run/lib/cjs/index.js:57:61
at process._tickCallback (internal/process/next_tick.js:61:11)
[1] [dev@arch-ehildenb klab]% klab server
fs.js:119
throw err;

Notice how it's requesting abstract-semantics.k from proof-hash b042... but we're actually running proof-hash dfc6.... This is a problem with how K caches compiled definitions, and must be fixed upstream.

To fix this, run:

make clean && make deps

This will remove and recompile the KEVM semantics.

Docker

Example usage:

# Build server
docker build -t klab .

# Start server and mount ./examples to /docker
docker run --rm -it -v $(pwd)/examples:/docker --name klab klab
klab server

# Start client
docker exec -it klab bash
cd /docker/SafeAdd
klab debug

License

All contributions to this repository are licensed under AGPL-3.0. Authors:

• Denis Erfurt
• Martin Lundfall
• Everett Hildenbrandt
• Lev Livnev