b0cf8c021f
... but turn it back on in CI by default. The `binaryen-sys` crate builds binaryen from source, which is a drag on CI for a few reasons: * This is quite large and takes a good deal of time to build * The debug build directory for binaryen is 4GB large In an effort to both save time and disk space on the builders this commit adds a `binaryen` feature to the `wasmtime-fuzz` crate. This feature is enabled specifically when running the fuzzers on CI, but it is disabled during the typical `cargo test --all` command. This means that the test builders should save an extra 4G of space and be a bit speedier now that they don't build a giant wad of C++. We'll need to update the OSS-fuzz integration to enable the `binaryen` feature when executing `cargo fuzz build`, and I'll do that once this gets closer to landing.
cargo fuzz Targets for Wasmtime
This crate defines various libFuzzer
fuzzing targets for Wasmtime, which can be run via cargo fuzz.
These fuzz targets just glue together pre-defined test case generators with
oracles and pass libFuzzer-provided inputs to them. The test case generators and
oracles themselves are independent from the fuzzing engine that is driving the
fuzzing process and are defined in wasmtime/crates/fuzzing.
Example
To start fuzzing run the following command, where $MY_FUZZ_TARGET is one of
the available fuzz targets:
cargo fuzz run $MY_FUZZ_TARGET
Available Fuzz Targets
At the time of writing, we have the following fuzz targets:
compile: Attempt to compile libFuzzer's raw input bytes with Wasmtime.instantiate: Attempt to compile and instantiate libFuzzer's raw input bytes with Wasmtime.instantiate_translated: Pass libFuzzer's input bytes towasm-opt -ttfto generate a random, valid Wasm module, and then attempt to instantiate it.
The canonical list of fuzz targets is the .rs files in the fuzz_targets
directory:
ls wasmtime/fuzz/fuzz_targets/
Corpora
While you can start from scratch, libFuzzer will work better if it is given a corpus of seed inputs to kick start the fuzzing process. We maintain a corpus for each of these fuzz targets in a dedicated repo on github.
You can use our corpora by cloning it and placing it at wasmtime/fuzz/corpus:
git clone \
https://github.com/bytecodealliance/wasmtime-libfuzzer-corpus.git \
wasmtime/fuzz/corpus