ff1af20479
Alignment on all memory instructions in wasm is currently best-effort and not actually required, meaning that whatever wasm actually uses as an address should work regardless of whether the address is aligned or not. This is theoretically tested in the fuzzers via wasm-smith-generated code, but wasm-smith doesn't today have too too high of a chance of generating an actual successful load/store. This commit adds a new configuration option to the `Config` generator for fuzzing which forces usage of a custom linear memory implementation which is backed by Rust's `Vec<u8>` and forces the base address of linear memory to be off-by-one relative to the base address of the `Vec<u8>` itself. This should theoretically force host addresses to almost always be unaligned, even if wasm addresses are otherwise aligned. The main interesting fuzz coverage here is likely to be in the existing `differential` target which compares running the same module in wasmtime with two different `Config` values to ensure the same results are produced. This probably won't increase coverage all that much in the near future due to wasm-smith rarely generating successful loads/stores, but in the meantime by hooking this up into `Config` it also means that we'll be running in comparison against v8 and also ensuring that all spec tests succeed if misalignment is forced at the hardware level. As a side effect this commit also cleans up the fuzzers slightly: * The `DifferentialConfig` struct is removed and folded into `Config` * The `init_hang_limit` processing is removed since we don't use `-ttf`-generated modules from binaryen any more. * Traps are now asserted to have the same trap code, otherwise differential fuzzing fails. * Some more debug logging was added to the differential fuzzer
Fuzzing Infrastructure for Wasmtime
This crate provides test case generators and oracles for use with fuzzing.
These generators and oracles are generally independent of the fuzzing engine
that might be using them and driving the whole fuzzing process (e.g. libFuzzer
or AFL). As such, this crate does not contain any actual fuzz targets
itself. Those are generally just a couple lines of glue code that plug raw input
from (for example) libFuzzer into a generator, and then run one or more
oracles on the generated test case.
If you're looking for the actual fuzz target definitions we currently have, they
live in wasmtime/fuzz/fuzz_targets/* and are driven by cargo fuzz and
libFuzzer.