# DeepState [![Slack Chat](http://empireslacking.herokuapp.com/badge.svg)](https://empireslacking.herokuapp.com/) [![Build Status](https://travis-ci.org/trailofbits/deepstate.svg?branch=master)](https://travis-ci.org/trailofbits/deepstate) DeepState is a framework that provides C and C++ developers with a common interface to various symbolic execution and fuzzing engines. Users can write one test harness using a Google Test-like API, then execute it using multiple backends without having to learn the complexities of the underlying engines. It supports writing unit tests and API sequence tests, as well as automatic test generation. Read more about the goals and design of DeepState in our [paper](https://agroce.github.io/bar18.pdf). The [2018 IEEE Cybersecurity Development Conference](https://secdev.ieee.org/2018/home) included a [full tutorial](https://github.com/trailofbits/publications/tree/master/workshops/DeepState:%20Bringing%20vulnerability%20detection%20tools%20into%20the%20development%20lifecycle%20-%20SecDev%202018) on effective use of DeepState. ## Overview of Features * Tests look like Google Test, but can use symbolic execution/fuzzing to generate data (parameterized unit testing) * Easier to learn than binary analysis tools/fuzzers, but provides similar functionality * Already supports Manticore, Angr, libFuzzer, file-based fuzzing with e.g., AFL; more back-ends likely in future * Switch test generation tool without re-writing test harness * Work around show-stopper bugs * Find out which tool works best for your code under test * Different tools find different bugs/vulnerabilities * Fair way to benchmark/bakeoff tools * Provides test replay for regression plus effective automatic test case reduction to aid debugging * Supports API-sequence generation with extensions to Google Test interface * Concise readable way (OneOf) to say "run one of these blocks of code" * Same construct supports fixed value set non-determinism * E.g., writing a POSIX file system tester is pleasant, not painful as in pure Google Test idioms * Provides high-level strategies for improving symbolic execution/fuzzing effectiveness * Pumping (novel to DeepState) to pick concrete values when symbolic execution is too expensive * Automatic decomposition of integer compares to guide coverage-driven fuzzers ## Supported Platforms DeepState currently targets Linux, with macOS support in progress (the fuzzers work fine, but symbolic execution is not well-supported yet, without a painful cross-compilation process). ## Dependencies Build: - CMake - GCC and G++ with multilib support - Python 2.7 - Setuptools Runtime: - Python 2.7 - Z3 (for the Manticore backend) ## Building on Ubuntu 16.04 (Xenial) ```shell sudo apt update && sudo apt-get install build-essential gcc-multilib g++-multilib cmake python python-setuptools libffi-dev z3 git clone https://github.com/trailofbits/deepstate deepstate mkdir deepstate/build && cd deepstate/build cmake ../ make ``` ## Installing Assuming the DeepState build resides in `$DEEPSTATE`, run the following commands to install the DeepState python package: ```shell virtualenv venv . venv/bin/activate python $DEEPSTATE/build/setup.py install ``` The `virtualenv`-enabled `$PATH` should now include two executables: `deepstate` and `deepstate-angr`. These are _executors_, which are used to run DeepState test binaries with specific backends (automatically installed as Python dependencies). The `deepstate` executor uses the Manticore backend while `deepstate-angr` uses angr. They share a common interface where you may specify a number of workers and an output directory for saving backend-generated test cases. You can check your build using the test binaries that were (by default) built and emitted to `deepstate/build/examples`. For example, to use angr to symbolically execute the `IntegerOverflow` test harness with 4 workers, saving generated test cases in a directory called `out`, you would invoke: ```shell deepstate-angr --num_workers 4 --output_test_dir out $DEEPSTATE/build/examples/IntegerOverflow ``` The resulting `out` directory should look something like: ``` out └── IntegerOverflow.cpp ├── SignedInteger_AdditionOverflow │   ├── a512f8ffb2c1bb775a9779ec60b699cb.fail │   └── f1d3ff8443297732862df21dc4e57262.pass └── SignedInteger_MultiplicationOverflow ├── 6a1a90442b4d898cb3fac2800fef5baf.fail └── f1d3ff8443297732862df21dc4e57262.pass ``` To run these tests, you can just use the native executable, e.g.: ```shell $DEEPSTATE/build/examples/IntegerOverflow --input_test_dir out ``` to run all the generated tests, or ```shell $DEEPSTATE/build/examples/IntegerOverflow --input_test_files_dir out/IntegerOverflow.cpp/SignedInteger_AdditionOverflow --input_which_test SignedInteger_AdditionOverflow ``` to run the tests in one directory (in this case, you want to specify which test to run, also). You can also run a single test, e.g.: ```shell $DEEPSTATE/build/examples/IntegerOverflow --input_test_file out/IntegerOverflow.cpp/SignedInteger_AdditionOverflow/a512f8ffb2c1bb775a9779ec60b699cb.fail--input_which_test SignedInteger_AdditionOverflow ``` In the absence of an `--input_which_test` argument, DeepState defaults to the last-defined test. Run the native executable with the `--help` argument to see all DeepState options. ## Usage DeepState consists of a static library, used to write test harnesses, and command-line _executors_ written in Python. At this time, the best documentation is in the [examples](/examples) and in our [paper](https://agroce.github.io/bar18.pdf). A more extensive example, using DeepState and libFuzzer to test a user-mode file system, is available [here](https://github.com/agroce/testfs); in particular the [Tests.cpp](https://github.com/agroce/testfs/blob/master/Tests.cpp) file and CMakeLists.txt show DeepState usage. ## Log Levels By default, DeepState is not very verbose about testing activity, other than failing tests. The `--log-level` argument lowers the threshold for output, with 0 = `DEBUG`, 1 = `TRACE` (output from the tests, including `printf`s), and 2 = INFO (DeepState messages, the default), 3 = `WARNING`, 4 = `ERROR`, and 5 = `EXTERNAL` (output from other programs such as libFuzzer), and 6 = `CRITICAL`/`FATAL` messages. ## A Note on Mac OS and Forking Normally, when running a test for replay or fuzzing, DeepState forks in order to cleanly handle crashes of a test. Unfortunately, `fork()` on mac OS is extremely slow. When using the built-in fuzzer or replaying tests, it is highly recommended to add the `--no_fork` option on mac OS, unless you need the added crash handling (that is, things aren't working without that option). ## Example Code ``` #include using namespace deepstate; /* Simple, buggy, run-length encoding that creates "human readable" * encodings by adding 'A'-1 to the count, and splitting at 26 */ char* encode(const char* input) { unsigned int len = strlen(input); char* encoded = (char*)malloc((len*2)+1); int pos = 0; if (len > 0) { unsigned char last = input[0]; int count = 1; for (int i = 1; i < len; i++) { if (((unsigned char)input[i] == last) && (count < 26)) count++; else { encoded[pos++] = last; encoded[pos++] = 64 + count; last = (unsigned char)input[i]; count = 1; } } encoded[pos++] = last; encoded[pos++] = 65; // Should be 64 + count } encoded[pos] = '\0'; return encoded; } char* decode(const char* output) { unsigned int len = strlen(output); char* decoded = (char*)malloc((len/2)*26); int pos = 0; for (int i = 0; i < len; i += 2) { for (int j = 0; j < (output[i+1] - 64); j++) { decoded[pos++] = output[i]; } } decoded[pos] = '\0'; return decoded; } // Can be (much) higher (e.g., > 1024) if we're using fuzzing, not symbolic execution #define MAX_STR_LEN 6 TEST(Runlength, EncodeDecode) { char* original = DeepState_CStrUpToLen(MAX_STR_LEN, "abcdef0123456789"); char* encoded = encode(original); ASSERT_LE(strlen(encoded), strlen(original)*2) << "Encoding is > length*2!"; char* roundtrip = decode(encoded); ASSERT_EQ(strncmp(roundtrip, original, MAX_STR_LEN), 0) << "ORIGINAL: '" << original << "', ENCODED: '" << encoded << "', ROUNDTRIP: '" << roundtrip << "'"; } ``` The code above (which can be found [here](https://github.com/trailofbits/deepstate/blob/master/examples/Runlen.cpp) shows an example of a DeepState test harness. Most of the code is just the functions to be tested. Using DeepState to test them requires: - including the DeepState C++ header and using the DeepState namespace - defining at least one TEST, with names - calling some DeepState APIs that produce data - in this example, we see the `DeepState_CStrUpToLen` call tells DeepState to produce a string that has up the `MAX_STR_LEN` characters, chosen from those present in hex strings. - optionally making some assertions about the correctness of the results - in this example, the `ASSERT_LE` and `ASSERT_EQ` checks - in the absence of any properties to check, DeepState can still look for memory safety violations, crashes, and other general categories of undesireable behavior, like any fuzzer ## Built-In Fuzzer Every DeepState executable provides a simple built-in fuzzer that generates tests using completely random data. Using this fuzzer is as simple as calling the native executable with the `--fuzz` argument. The fuzzer also takes a `seed` and `timeout` (default of two minutes) to control the fuzzing. If you want to actually save the test cases generated, you need to add a `--output_test_dir` arument to tell DeepState where to put the generated tests. By default fuzzing saves only failing and crashing tests and only when given an output directory. Note that while symbolic execution only works on Linux, without a fairly complex cross-compliation process, the brute force fuzzer works on macOS or (as far as we know) any Unix-like system. ## Fuzzing with libFuzzer If you install clang 6.0 or later, and run `cmake` when you install with the `BUILD_LIBFUZZER` environment variable defined, you can generate tests using libFuzzer. Because both DeepState and libFuzzer want to be `main`, this requires building a different executable for libFuzzer. The `examples` directory shows how this can be done. The libFuzzer executable works like any other libFuzzer executable, and the tests produced can be replayed using the normal DeepState executable. For example, generating some tests of the `OneOf` example (up to 5,000 runs), then running those tests to examine the results, would look like: ```shell mkdir OneOf_libFuzzer_corpus ./OneOf_LF -runs=5000 OneOf_libFuzzer_corpus ./OneOf --input_test_files_dir OneOf_libFuzzer_corpus ``` Use the `LIBFUZZER_WHICH_TEST` environment variable to control which test libFuzzer runs, using a fully qualified name (e.g., `Arithmetic_InvertibleMultiplication_CanFail`). By default, you get the last test defined (which works fine if there is only one test). Obviously, libFuzzer may work better if you provide a non-empty corpus, but fuzzing will work even without an initial corpus, unlike AFL. One hint when using libFuzzer is to avoid dynamically allocating memory during a test, if that memory would not be freed on a test failure. This will leak memory and libFuzzer will run out of memory very quickly in each fuzzing session. Using libFuzzer on macOS requires compiling DeepState and your program with a clang that supports libFuzzer (which the Apple built-in probably won't); this can be as simple as doing: ```shell brew install llvm@6 CC=/usr/local/opt/llvm\@6/bin/clang CXX=/usr/local/opt/llvm\@6/bin/clang++ BUILD_LIBFUZZER=TRUE cmake .. make install ``` Other ways of getting an appropriate LLVM may also work. ## Test case reduction While tests generated by symbolic execution are likely to be highly concise already, fuzzer-generated tests may be much larger than they need to be. DeepState provides a test case reducer to shrink tests intelligently, aware of the structure of a DeepState test. For example, if your executable is named `TestFileSystem` and the test you want to reduce is named `rmdirfail.test` you would use it like this: ```shell deepstate-reduce ./TestFileSystem rmdirfail.test minrmdirfail.test ``` In many cases, this will result in finding a different failure or crash that allows smaller test cases, so you can also provide a string that controls the criteria for which test outputs are considered valid reductions (by default, the reducer looks for any test that fails or crashes). Only outputs containing the `--criteria` are considered to be valid reductions: ```shell deepstate-reduce ./TestFileSystem rmdirfail.test minrmdirfail.test --criteria "FATAL: /root/testfs/super.c(252)" ``` The output will look something like: ``` ORIGINAL TEST HAS 119 BYTES ONEOF REMOVAL REDUCED TEST TO 103 BYTES ONEOF REMOVAL REDUCED TEST TO 87 BYTES ONEOF REMOVAL REDUCED TEST TO 67 BYTES ONEOF REMOVAL REDUCED TEST TO 51 BYTES BYTE RANGE REMOVAL REDUCED TEST TO 50 BYTES BYTE RANGE REMOVAL REDUCED TEST TO 49 BYTES BYTE REDUCTION: BYTE 3 FROM 4 TO 0 BYTE REDUCTION: BYTE 43 FROM 4 TO 0 ONEOF REMOVAL REDUCED TEST TO 33 BYTES ONEOF REMOVAL REDUCED TEST TO 17 BYTES BYTE REDUCTION: BYTE 7 FROM 2 TO 1 BYTE REDUCTION: BYTE 15 FROM 2 TO 1 NO REDUCTIONS FOUND PADDING TEST WITH 3 ZEROS WRITING REDUCED TEST WITH 20 BYTES TO minrmdirfail.test ``` You can use `--which_test ` to specify which test to run, as with the `--input_which_test` options to test replay. Test case reduction should work on any OS. ## Fuzzing with AFL DeepState can also be used with a file-based fuzzer (e.g. AFL). There are a few steps to this. First, compile DeepState itself with any needed instrumentation. E.g., to use it with AFL, you might want to add something like: ``` SET(CMAKE_C_COMPILER /usr/local/bin/afl-gcc) SET(CMAKE_CXX_COMPILER /usr/local/bin/afl-g++) ``` to `deepstate/CMakeLists.txt`. Second, do the same for your DeepState test harness and any code it links to you want instrumented. Finally, run the fuzzing via the interface to replay test files. For example, to fuzz the `OneOf` example, if we were in the `deepstate/build/examples` directory, you would do something like: ```shell afl-fuzz -d -i corpus -o afl_OneOf -- ./OneOf --input_test_file @@ --abort_on_fail ``` where `corpus` contains at least one file to start fuzzing from. The file needs to be smaller than the DeepState input size limit, but has few other limitations (for AFL it should also not cause test failure). The `abort_on_fail` flag makes DeepState crashes and failed tests appear as crashes to the fuzzer. To replay the tests from AFL: ```shell ./OneOf --input_test_files_dir afl_OneOf/crashes ./OneOf --input_test_files_dir afl_OneOf/queue ``` Finally, if an example has more than one test, you need to specify, with a fully qualified name (e.g., `Arithmetic_InvertibleMultiplication_CanFail`), which test to run, using the `--input_which_test` flag to the binary. By default, DeepState will run the last test defined. You can compile with `afl-clang-fast` and `afl-clang-fast++` for deferred instrumentation. You'll need code like: ``` #ifdef __AFL_HAVE_MANUAL_CONTROL __AFL_INIT(); #endif ``` just before the call to `DeepState_Run()` (which reads the entire input file) in your `main`. Because AFL and other file-based fuzzers only rely on the DeepState native test executable, they should (like DeepState's built-in simple fuzzer) work fine on macOS and other Unix-like OSes. ## Contributing All accepted PRs are awarded bounties by Trail of Bits. Join the #deepstate channel on the [Empire Hacking Slack](https://empireslacking.herokuapp.com/) to discuss ongoing development and claim bounties. Check the [good first issue](https://github.com/trailofbits/deepstate/issues?q=is%3Aissue+is%3Aopen+label%3A%22good+first+issue%22) label for suggested contributions. ## License DeepState is released under [The Apache License 2.0](LICENSE).