datAFLow

DatAFLow is a fuzzer built on top of AFL++. However, instead of a control-flow-based feedback mechanism (e.g., based on control-flow edge coverage), datAFLow uses a data-flow-based feedback mechanism; specifically, data flows based on def-use associations.

To enable performant fuzzing, datAFLow uses a flexible and efficient memory object metadata scheme based on the "Padding Area MetaData" (PAMD) approach.

More details are available in our registered report, published at the 1st International Fuzzing Workshop (FUZZING) 2022, and in our TOSEM paper. You can read the report here and the final journal paper here.

Requirements

datAFLow is built on LLVM v12-14. Python is also required (for the dataflow-cc wrapper).

Building z3

Z3 is required by SVF (for static analysis). SVF is an optional component. If running datAFLow on Ubuntu 20.04, you can install z3 via apt.

git clone https://github.com/z3prover/z3
git -C z3 checkout z3-4.8.8
mkdir -p z3/build
cd z3/build
cmake .. \
    -DCMAKE_INSTALL_PREFIX=$(realpath ../install) -DZ3_BUILD_LIBZ3_SHARED=False
make -j
make install

Building fuzzalloc

FUZZALLOC_SRC variable refers to this directory (i.e., the root source directory). Ensure all submodules are initialized.

cd $FUZZALLOC_SRC
git submodule update --init --recursive

Then build.

cd $FUZZALLOC_SRC
mkdir build
cd build
cmake .. \
    -DCMAKE_C_COMPILER=clang-12 -DCMAKE_CXX_COMPILER=clang++-12 \
    -DLLVM_DIR=$(llvm-config-12 --cmakedir) \
    -DZ3_DIR=/path/to/z3/install
make -j

To build the SVF-based static analysis, pass the -DUSE_SVF=True option to cmake. As described above, SVF requires z3. If z3 was built from source, the -DZ3_DIR=/path/to/z3/install option is also required.

Instrumenting a Target

The dataflow-cc (and dataflow-cc++) tools can be used as dropin replacements for clang (and clang++). These wrappers provide a number of environment variables to configure the target:

• FUZZALLOC_DEF_MEM_FUNCS: Path to a special case list (see below) listing custom memory allocation routines

• FUZZALLOC_DEF_SENSITIVITY: The def sites to instrument. One of array, struct, or array:struct.

• FUZZALLOC_USE_SENSITIVITY: The use sites to instrument. One of read, write, or read:write.

• FUZZALLOC_USE_CAPTURE: What to capture at each use site. One of use, offset, or value.

• FUZZALLOC_INST: Instrumentation. One of: afl (for fuzzing); tracer (for accurate tracing of def-use chains); or none.

Custom memory allocators

If the target uses custom memory allocation routines (i.e., wrapping malloc, calloc, etc.), then a special case list containing a list of these routines should be provided to dataflow-preprocess. Doing so ensures dynamically-allocated variable def sites are appropriately tagged. The list is provided via the --def-mem-funcs option. The special case list must be formatted as:

[fuzzalloc]
fun:malloc_wrapper
fun:calloc_wrapper
fun:realloc_wrapper

Tools

In addition to dataflow-cc and dataflow-c++, we provide the following tools:

static-dua

Uses SVF to statically derive an upper bounds on the number of def-use chains in a BC file. This tool generates JSON output tying these def-use chains to source-level variables (recovered through debug info).

Note that you must run CMake with the -DUSE_SVF=On option to build this tool.

dataflow-stats

Collect fuzzalloc stats from an instrumented bitcode file. Stats include: number of tagged variables, number of instrumented use sites, etc.

static-region-cov

static-region-cov statically extracts Clang's source-based code coverage from an instrumented binary.

dua-cov-json

Generate data-flow coverage over time from an AFL++ queue output directory. Relies on a version of the target program instrumented with trace mode (i.e., setting FUZZALLOC_INST=trace) to replay the queue through, generating JSON reports logging covered def-use chains.

llvm-cov-json

Generate control-flow coverage over time from an AFL++ queue output directory. Relies on a version of the target program instrumented with Clang's source-based coverage (i.e., compiled using Clang's -fprofile-instr-generate -fcoverage-mapping flags) to replay the queue through, generating JSON reports logging covered def-use chains.

Evaluation Reproduction

See README.magma.md and README.ddfuzz.md for reproducing the Magma and DDFuzz experiments, respectively.