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diff --git a/doc/fuzzing.md b/doc/fuzzing.md index 5dedcb51c8..08b73d3b3c 100644 --- a/doc/fuzzing.md +++ b/doc/fuzzing.md @@ -1,12 +1,13 @@ Fuzz-testing Bitcoin Core ========================== -A special test harness `test_bitcoin_fuzzy` is provided to provide an easy -entry point for fuzzers and the like. In this document we'll describe how to -use it with AFL. +A special test harness in `src/test/fuzz/` is provided for each fuzz target to +provide an easy entry point for fuzzers and the like. In this document we'll +describe how to use it with AFL and libFuzzer. -Building AFL -------------- +## AFL + +### Building AFL It is recommended to always use the latest version of afl: ``` @@ -17,16 +18,15 @@ make export AFLPATH=$PWD ``` -Instrumentation ----------------- +### Instrumentation To build Bitcoin Core using AFL instrumentation (this assumes that the `AFLPATH` was set as above): ``` -./configure --disable-ccache --disable-shared --enable-tests CC=${AFLPATH}/afl-gcc CXX=${AFLPATH}/afl-g++ +./configure --disable-ccache --disable-shared --enable-tests --enable-fuzz CC=${AFLPATH}/afl-gcc CXX=${AFLPATH}/afl-g++ export AFL_HARDEN=1 cd src/ -make test/test_bitcoin_fuzzy +make ``` We disable ccache because we don't want to pollute the ccache with instrumented objects, and similarly don't want to use non-instrumented cached objects linked @@ -35,12 +35,11 @@ in. The fuzzing can be sped up significantly (~200x) by using `afl-clang-fast` and `afl-clang-fast++` in place of `afl-gcc` and `afl-g++` when compiling. When compiling using `afl-clang-fast`/`afl-clang-fast++` the resulting -`test_bitcoin_fuzzy` binary will be instrumented in such a way that the AFL +binary will be instrumented in such a way that the AFL features "persistent mode" and "deferred forkserver" can be used. See https://github.com/mcarpenter/afl/tree/master/llvm_mode for details. -Preparing fuzzing ------------------- +### Preparing fuzzing AFL needs an input directory with examples, and an output directory where it will place examples that it found. These can be anywhere in the file system, @@ -60,13 +59,30 @@ Example inputs are available from: Extract these (or other starting inputs) into the `inputs` directory before starting fuzzing. -Fuzzing --------- +### Fuzzing To start the actual fuzzing use: ``` -$AFLPATH/afl-fuzz -i ${AFLIN} -o ${AFLOUT} -m52 -- test/test_bitcoin_fuzzy +$AFLPATH/afl-fuzz -i ${AFLIN} -o ${AFLOUT} -m52 -- test/fuzz/fuzz_target_foo ``` You may have to change a few kernel parameters to test optimally - `afl-fuzz` will print an error and suggestion if so. + +## libFuzzer + +A recent version of `clang`, the address sanitizer and libFuzzer is needed (all +found in the `compiler-rt` runtime libraries package). + +To build the `test/test_bitcoin_fuzzy` executable run + +``` +./configure --disable-ccache --enable-fuzz --with-sanitizers=fuzzer,address CC=clang CXX=clang++ +make +``` + +The fuzzer needs some inputs to work on, but the inputs or seeds can be used +interchangeably between libFuzzer and AFL. + +See https://llvm.org/docs/LibFuzzer.html#running on how to run the libFuzzer +instrumented executable. |