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 proofs in the K Framework, tailored for the formal verification of ethereum smart contracts. It includes a succinct specification language for expressing the behavior of ethereum contracts, and an interactive debugger.

Installation

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 parallel

On ArchLinux:

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

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 gnu-getopt

This project uses gnu-getopt for dealing with argument handling. OSX and gnu have a complicated relationship but you can run:

export PATH=/usr/local/opt/gnu-getopt/bin:$PATH

to make them get along.

Building

Clone the repo and install the latest stable version v0.2.4 with

git clone --branch v0.2.4 https://github.com/dapphub/klab.git
cd klab
make deps

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

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

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.

OPTIONAL: You might also want to add the K tool binaries in evm-semantics/.build/k/k-distribution/bin to your $PATH, if you didn't already have K installed.

OPTIONAL: You can also use nix-shell for a more deterministic environment experience. If you have nix installed, run nix-shell in this repo to start a deterministic shell environment.

Usage

To see how klab is used, we can explore the project in examples/SafeAdd:

cd examples/SafeAdd/

Specification

The file config.json tells klab where to look for both the specification and the implementation of our contract. In this case, our specification lives in src/, and our implementation lives in dapp/.

Note that this example includes dapp/out/SafeAdd.sol.json compiled from the solidity source. With solc installed, you can compile it yourself:

solc --combined-json=abi,bin,bin-runtime,srcmap,srcmap-runtime,ast dapp/src/SafeAdd.sol > dapp/out/SafeAdd.sol.json

Proof

Our goal is to prove that our implementation satisfies our specification. To do so, we'll start by building a set of K modules from our spec:

klab build

This will generate success and failure reachability rules for each act of our specification. We can find the results in the out/specs directory.

Now we're ready to prove each case, for example:

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

The --dump flag outputs a log to out/data/<hash>.log, which will be needed later for interactive debugging. We can also do klab prove-all to prove all outstanding claims.

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

klab debug <hash>

The output might be somewhat hard to use, due to the massive amount of branches related to gas, you can filter out gas related branches:

klab debug --filter-oog $(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.

License

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

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