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Diffstat (limited to 'doc/fuzzing.md')
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1 files changed, 38 insertions, 29 deletions
diff --git a/doc/fuzzing.md b/doc/fuzzing.md index 23317e938e..f9221dde5b 100644 --- a/doc/fuzzing.md +++ b/doc/fuzzing.md @@ -1,9 +1,32 @@ 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 and libFuzzer. +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. + +## 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, +we'll define environment variables to make it easy to reference them. + +libFuzzer will use the input directory as output directory. + +Extract the example seeds (or other starting inputs) into the inputs +directory before starting fuzzing. + +``` +git clone https://github.com/bitcoin-core/qa-assets +export DIR_FUZZ_IN=$PWD/qa-assets/fuzz_seed_corpus +``` + +Only for AFL: + +``` +mkdir outputs +export AFLOUT=$PWD/outputs +``` ## AFL @@ -23,10 +46,10 @@ export AFLPATH=$PWD To build Bitcoin Core using AFL instrumentation (this assumes that the `AFLPATH` was set as above): ``` -./configure --disable-ccache --disable-shared --enable-tests CC=${AFLPATH}/afl-gcc CXX=${AFLPATH}/afl-g++ +./configure --disable-ccache --disable-shared --enable-tests --enable-fuzz --disable-wallet --disable-bench --with-utils=no --with-daemon=no --with-libs=no --with-gui=no CC=${AFLPATH}/afl-gcc CXX=${AFLPATH}/afl-g++ export AFL_HARDEN=1 cd src/ -make test/test_bitcoin_fuzzy +make ``` We disable ccache because we don't want to pollute the ccache with instrumented objects, and similarly don't want to use non-instrumented cached objects linked @@ -35,35 +58,18 @@ in. The fuzzing can be sped up significantly (~200x) by using `afl-clang-fast` and `afl-clang-fast++` in place of `afl-gcc` and `afl-g++` when compiling. When compiling using `afl-clang-fast`/`afl-clang-fast++` the resulting -`test_bitcoin_fuzzy` binary will be instrumented in such a way that the AFL +binary will be instrumented in such a way that the AFL features "persistent mode" and "deferred forkserver" can be used. See https://github.com/mcarpenter/afl/tree/master/llvm_mode for details. -### Preparing fuzzing - -AFL needs an input directory with examples, and an output directory where it -will place examples that it found. These can be anywhere in the file system, -we'll define environment variables to make it easy to reference them. - -``` -mkdir inputs -AFLIN=$PWD/inputs -mkdir outputs -AFLOUT=$PWD/outputs -``` - -Example inputs are available from: - -- https://download.visucore.com/bitcoin/bitcoin_fuzzy_in.tar.xz -- http://strateman.ninja/fuzzing.tar.xz - -Extract these (or other starting inputs) into the `inputs` directory before starting fuzzing. - ### Fuzzing To start the actual fuzzing use: + ``` -$AFLPATH/afl-fuzz -i ${AFLIN} -o ${AFLOUT} -m52 -- test/test_bitcoin_fuzzy +export FUZZ_TARGET=fuzz_target_foo # Pick a fuzz_target +mkdir ${AFLOUT}/${FUZZ_TARGET} +$AFLPATH/afl-fuzz -i ${DIR_FUZZ_IN}/${FUZZ_TARGET} -o ${AFLOUT}/${FUZZ_TARGET} -m52 -- test/fuzz/${FUZZ_TARGET} ``` You may have to change a few kernel parameters to test optimally - `afl-fuzz` @@ -74,10 +80,10 @@ will print an error and suggestion if so. A recent version of `clang`, the address sanitizer and libFuzzer is needed (all found in the `compiler-rt` runtime libraries package). -To build the `test/test_bitcoin_fuzzy` executable run +To build all fuzz targets with libFuzzer, run ``` -./configure --disable-ccache --with-sanitizers=fuzzer,address CC=clang CXX=clang++ +./configure --disable-ccache --disable-wallet --disable-bench --with-utils=no --with-daemon=no --with-libs=no --with-gui=no --enable-fuzz --with-sanitizers=fuzzer,address CC=clang CXX=clang++ make ``` @@ -86,3 +92,6 @@ interchangeably between libFuzzer and AFL. See https://llvm.org/docs/LibFuzzer.html#running on how to run the libFuzzer instrumented executable. + +Alternatively run the script in `./test/fuzz/test_runner.py` and provide it +with the `${DIR_FUZZ_IN}` created earlier. |