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doc/fuzzing.md
Fuzz-testing Bitcoin ABC | Fuzz-testing Bitcoin ABC | ||||
========================== | ========================== | ||||
A special test harness in `src/test/fuzz/` is provided for each fuzz target to | 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 | provide an easy entry point for fuzzers and the like. In this document we'll | ||||
describe how to use it with AFL and libFuzzer. | 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-ABC/qa-assets | |||||
export DIR_FUZZ_IN=$PWD/qa-assets/fuzz_seed_corpus | |||||
``` | |||||
Only for AFL: | |||||
``` | |||||
mkdir outputs | |||||
export AFLOUT=$PWD/outputs | |||||
``` | |||||
## AFL | ## AFL | ||||
### Building AFL | ### Building AFL | ||||
It is recommended to always use the latest version of afl: | It is recommended to always use the latest version of afl: | ||||
``` | ``` | ||||
wget http://lcamtuf.coredump.cx/afl/releases/afl-latest.tgz | wget http://lcamtuf.coredump.cx/afl/releases/afl-latest.tgz | ||||
tar -zxvf afl-latest.tgz | tar -zxvf afl-latest.tgz | ||||
Show All 20 Lines | |||||
The fuzzing can be sped up significantly (~200x) by using `afl-clang-fast` and | 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 | `afl-clang-fast++` in place of `afl-gcc` and `afl-g++` when compiling. When | ||||
compiling using `afl-clang-fast`/`afl-clang-fast++` the resulting | compiling using `afl-clang-fast`/`afl-clang-fast++` the resulting | ||||
binary will be instrumented in such a way that the AFL features "persistent | binary will be instrumented in such a way that the AFL features "persistent | ||||
mode" and "deferred forkserver" can be used. | mode" and "deferred forkserver" can be used. | ||||
See https://github.com/mcarpenter/afl/tree/master/llvm_mode for details. | 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 | |||||
Extract these (or other starting inputs) into the `inputs` directory before starting fuzzing. | |||||
### Fuzzing | ### Fuzzing | ||||
To start the actual fuzzing use: | To start the actual fuzzing use: | ||||
``` | ``` | ||||
$AFLPATH/afl-fuzz -i ${AFLIN} -o ${AFLOUT} -m52 -- src/test/fuzz/fuzz_target_foo | 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 -- src/test/fuzz/${FUZZ_TARGET} | |||||
``` | ``` | ||||
You may have to change a few kernel parameters to test optimally - `afl-fuzz` | You may have to change a few kernel parameters to test optimally - `afl-fuzz` | ||||
will print an error and suggestion if so. | will print an error and suggestion if so. | ||||
## libFuzzer | ## libFuzzer | ||||
A recent version of `clang`, the address sanitizer and libFuzzer is needed (all | A recent version of `clang`, the address sanitizer and libFuzzer is needed (all | ||||
found in the `compiler-rt` runtime libraries package). | found in the `compiler-rt` runtime libraries package). | ||||
To build the `test/test_bitcoin_fuzzy` executable run | To build all fuzz targets with libFuzzer, run | ||||
``` | ``` | ||||
mkdir -p buildFuzzer | mkdir -p buildFuzzer | ||||
cd buildFuzzer | cd buildFuzzer | ||||
cmake -GNinja .. \ | cmake -GNinja .. \ | ||||
-DCCACHE=OFF \ | -DCCACHE=OFF \ | ||||
-DCMAKE_C_COMPILER=clang \ | -DCMAKE_C_COMPILER=clang \ | ||||
-DCMAKE_CXX_COMPILER=clang++ \ | -DCMAKE_CXX_COMPILER=clang++ \ | ||||
-DENABLE_SANITIZERS="fuzzer;address" | -DENABLE_SANITIZERS="fuzzer;address" | ||||
ninja bitcoin-fuzzers | ninja bitcoin-fuzzers | ||||
``` | ``` | ||||
The fuzzer needs some inputs to work on, but the inputs or seeds can be used | The fuzzer needs some inputs to work on, but the inputs or seeds can be used | ||||
interchangeably between libFuzzer and AFL. | interchangeably between libFuzzer and AFL. | ||||
See https://llvm.org/docs/LibFuzzer.html#running on how to run the libFuzzer | See https://llvm.org/docs/LibFuzzer.html#running on how to run the libFuzzer | ||||
instrumented executable. | instrumented executable. | ||||
Alternatively run the script in `./test/fuzz/test_runner.py` and provide it | |||||
with the `${DIR_FUZZ_IN}` created earlier. |