build: Allow to configure --with-sanitizers=fuzzer
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2 changed files with 33 additions and 10 deletions
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@ -295,7 +295,14 @@ if test x$use_sanitizers != x; then
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AX_CHECK_LINK_FLAG(
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[[-fsanitize=$use_sanitizers]],
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[[SANITIZER_LDFLAGS=-fsanitize=$use_sanitizers]],
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[AC_MSG_ERROR([linker did not accept requested flags, you are missing required libraries])])
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[AC_MSG_ERROR([linker did not accept requested flags, you are missing required libraries])],
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[],
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[AC_LANG_PROGRAM([[
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#include <cstdint>
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#include <cstddef>
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extern "C" int LLVMFuzzerTestOneInput(const uint8_t *data, size_t size) { return 0; }
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__attribute__((weak)) // allow for libFuzzer linking
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]],[[]])])
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fi
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ERROR_CXXFLAGS=
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@ -3,10 +3,11 @@ Fuzz-testing Bitcoin Core
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A special test harness `test_bitcoin_fuzzy` is provided to provide an easy
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entry point for fuzzers and the like. In this document we'll describe how to
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use it with AFL.
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use it with AFL and libFuzzer.
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Building AFL
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-------------
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## AFL
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### Building AFL
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It is recommended to always use the latest version of afl:
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```
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@ -17,8 +18,7 @@ make
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export AFLPATH=$PWD
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```
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Instrumentation
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----------------
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### Instrumentation
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To build Bitcoin Core using AFL instrumentation (this assumes that the
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`AFLPATH` was set as above):
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@ -39,8 +39,7 @@ compiling using `afl-clang-fast`/`afl-clang-fast++` the resulting
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features "persistent mode" and "deferred forkserver" can be used. See
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https://github.com/mcarpenter/afl/tree/master/llvm_mode for details.
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Preparing fuzzing
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------------------
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### Preparing fuzzing
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AFL needs an input directory with examples, and an output directory where it
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will place examples that it found. These can be anywhere in the file system,
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@ -60,8 +59,7 @@ Example inputs are available from:
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Extract these (or other starting inputs) into the `inputs` directory before starting fuzzing.
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Fuzzing
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--------
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### Fuzzing
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To start the actual fuzzing use:
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```
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@ -70,3 +68,21 @@ $AFLPATH/afl-fuzz -i ${AFLIN} -o ${AFLOUT} -m52 -- test/test_bitcoin_fuzzy
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You may have to change a few kernel parameters to test optimally - `afl-fuzz`
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will print an error and suggestion if so.
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## libFuzzer
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A recent version of `clang`, the address sanitizer and libFuzzer is needed (all
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found in the `compiler-rt` runtime libraries package).
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To build the `test/test_bitcoin_fuzzy` executable run
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```
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./configure --disable-ccache --with-sanitizers=fuzzer,address CC=clang CXX=clang++
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make
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```
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The fuzzer needs some inputs to work on, but the inputs or seeds can be used
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interchangably between libFuzzer and AFL.
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See https://llvm.org/docs/LibFuzzer.html#running on how to run the libFuzzer
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instrumented executable.
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