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78 lines
2.8 KiB
Markdown
78 lines
2.8 KiB
Markdown
# Fuzz Testing trezor-crypto
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Selected functions can be fuzzed via specific libFuzzer harnesses for increased test coverage and issue detection.
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Note: the following commands are relative to the trezor-crypto main directory.
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## Build
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A modern C compiler with built-in libFuzzer support is required. The build process will use `clang` by default.
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Set the `CC=` environment variable if you want to use a special compiler variant.
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```bash
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make clean
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FUZZER=1 make fuzzer
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```
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### Sanitizers
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Recommended: ASAN / UBSAN / MSAN flags for error detection can be specified via the special `SANFLAGS`.
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Examples:
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* `SANFLAGS="-fsanitize=address,undefined"`
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* `SANFLAGS="-fsanitize=memory -fsanitize-memory-track-origins"`
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### Optimizations
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Override `OPTFLAGS` to test the library at different optimization levels or simplify the debugging of detected issues.
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Examples:
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* `OPTFLAGS="-O0 -ggdb3"`
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* `OPTFLAGS="-O3 -march=native"`
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### Other Flags
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To be determined:
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* `-DNDEBUG`
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* `-DUSE_BIP39_CACHE=0 -DUSE_BIP32_CACHE=0`
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## Operation
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See the [libFuzzer documentation](https://llvm.org/docs/LibFuzzer.html#options) for valid options and usage. Detailed fuzzer usage and relevant considerations are out of scope of this document.
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**Warning**: fuzzing is resource-intensive and can have a negative impact on your system stability.
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Basic fuzzer call:
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```bash
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./fuzzer/fuzzer
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```
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Here is a more sophisticated multithreading example with a persistent input corpus and other optimizations:
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```bash
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mkdir fuzzer/fuzzer_corpus
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./fuzzer/fuzzer -max_len=2048 -use_value_profile=1 -jobs=16 -timeout=1 -reload=5 -print_pcs=1 -print_funcs=42 fuzzer/fuzzer_corpus
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```
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Hint: for more permanent setups, consider invoking the fuzzer from outside of the source directory to avoid cluttering it with logfiles and crash inputs. Similarly, it is recommended to store the fuzzer corpus in another location.
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## Automated Fuzzer Dictionary Generation
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[Dictionaries](https://llvm.org/docs/LibFuzzer.html#dictionaries) are a useful mechanism to augment the capabilities of the fuzzer. Specify them via the `-dict=` flag.
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### Collect Interesting Strings From Unit Tests
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```bash
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cd fuzzer
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./extract_fuzzer_dictionary.sh fuzzer_crypto_tests_strings_dictionary1.txt
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```
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The resulting file can be used as a fuzzer dictionary.
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## Evaluate Source Coverage
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1. build the fuzzer binary with `CFLAGS="-fprofile-instr-generate -fcoverage-mapping"`
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1. run with suitable `-runs=` or `-max_total_time=` limits
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1. convert the recorded data `llvm-profdata merge -output=default.profdata -instr default.profraw`
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1. render the data `llvm-cov show fuzzer/fuzzer -instr-profile=default.profdata -format=html -output-dir=coverage-report`
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1. analyze report at `coverage-report/index.html`
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1. (optional) remove artifacts with `rm default.profraw default.profdata && rm -r coverage-report`
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