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fuzzing.md

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Fuzzing

Fuzz tests use libFuzzer to test the SAPI _Prepare and _Complete functions.

Building fuzz tests can be enabled using the --with-fuzzing= option. For which there are two possible values.

libFuzzer

libFuzzer tests can be built natively or using the docker fuzzing target.

Natively

Build the fuzz tests by setting --with-fuzzing=libfuzzer and statically linking to the fuzzing TCTI.

export GEN_FUZZ=1

./bootstrap
./configure \
  CC=clang \
  CXX=clang++ \
  --enable-debug \
  --with-fuzzing=libfuzzer \
  --enable-tcti-fuzzing \
  --enable-tcti-device=no \
  --enable-tcti-mssim=no \
  --with-maxloglevel=none \
  --disable-shared

make -j $(nproc) check

Run the fuzz tests by executing any binary ending in .fuzz in test/fuzz/.

./test/fuzz/Tss2_Sys_ZGen_2Phase_Prepare.fuzz

Docker

Build the fuzz targets and check that they work by building the fuzzing docker target.

docker build --target fuzzing -t tpm2-tss:fuzzing .

Run a fuzz target and mount a directory as a volume into the container where it should store its findings should it produce any.

docker run --rm -ti tpm2-tss:fuzzing \
   -v "${PWD}/findings_dir":/artifacts \
   ./test/fuzz/Tss2_Sys_PolicyPhysicalPresence_Prepare.fuzz \
  -artifact_prefix=/artifacts

OSS Fuzz

OSS fuzz integration can be found under the tpm2-tss project in OSS Fuzz.

The Dockerfile there builds the dependencies. build.sh Runs the compilation as seen under the fuzzing target of the Dockerfile in this repo, only --with-fuzzing=ossfuzz.

Hacking

Currently only fuzz targets for the System API have been implemented.

TCTI

The fuzzing TCTI is used as a temporary storage location for the Data and Size arguments of LLVMFuzzerTestOneInput.

For _Complete calls the TCTI uses Data and Size as the response buffer and response size for TSS2_TCTI_RECEIVE.

SAPI

Fuzz tests are generated via script/gen_fuzz.py.

Setting GEN_FUZZ=1 when running bootstrap will run script/gen_fuzz.py.

GEN_FUZZ=1 ./bootstrap

script/gen_fuzz.py reads the SAPI header file and generates a fuzz target for each _Prepare and _Complete call using similar templates.

For _Prepare calls the fuzz_fill function in the fuzzing TCTI will fill each TPM2 structure used can copy from LLVMFuzzerTestOneInput's Data into it.