Written by Andrea Fioraldi [email protected]
This Linux-only companion library allows you to instrument strcmp(), memcmp(),
and related functions to log the CompareCoverage of these libcalls.
Use this with caution. While this can speedup a lot the bypass of hard branch conditions it can also waste a lot of time and take up unnecessary space in the shared memory when logging the coverage related to functions that doesn't process input-related data.
To use the library, you need to make sure that your fuzzing target is linked dynamically and make use of strcmp(), memcmp(), and related functions. For optimized binaries this is an issue, those functions are often inlined and this module is not capable to log the coverage in this case.
If you have the source code of the fuzzing target you should nto use this library and QEMU but build it with afl-clang-fast and the laf-intel options.
To use this library, make sure to preload it with AFL_PRELOAD.
export AFL_PRELOAD=/path/to/libcompcov.so
export AFL_COMPCOV_LEVEL=1
afl-fuzz -Q -i input -o output <your options> -- <target args>
The AFL_COMPCOV_LEVEL tells to QEMU and libcompcov how to log comaprisons. Level 1 logs just comparison with immediates / read-only memory and level 2 logs all the comparisons.
The library makes use of https://github.com/ouadev/proc_maps_parser and so it is Linux specific. However, this is not a strict dependency, other UNIX operating systems can be supported by replacing the code related to the /proc/self/maps parsing.