bbdea06e2d
This PR adds a new fuzz target, `differential_wasmi`, that runs a Cranelift-based Wasm backend alongside a simple third-party Wasm interpeter crate (`wasmi`). The fuzzing runs the first function in a given module to completion on each side, and then diffs the return value and linear memory contents. This strategy should provide end-to-end coverage including both the Wasm translation to CLIF (which has seen some subtle and scary bugs at times), the lowering from CLIF to VCode, the register allocation, and the final code emission. This PR also adds a feature `experimental_x64` to the fuzzing crate (and the chain of dependencies down to `cranelift-codegen`) so that we can fuzz the new x86-64 backend as well as the current one.
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