117 lines
4.4 KiB
Markdown
117 lines
4.4 KiB
Markdown
# Fuzzing
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This directory contains coverage-guided fuzzers for KZG functions. It uses
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LLVM's [libFuzzer](https://llvm.org/docs/LibFuzzer.html) for the heavy lifting.
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Each directory is named after a target and contains a single file (`fuzz.c`)
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that implements a `LLVMFuzzerTestOneInput` function. These are relatively
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simple; if the input matches the size requirements, it passes the data to the
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target function. There is a Makefile that compiles and starts the fuzzer, which
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means it should be pretty easy.
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## Dependencies
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This is expected to run on Linux/macOS, it is not expected to work on Windows.
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In addition to `build-essentials` and `clang`, this requires `llvm` to be
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installed:
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### Linux
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```
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sudo apt install llvm
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```
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### macOS
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```
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brew install llvm
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```
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## Targets
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Currently, only the public KZG interface functions are fuzzable:
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```
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$ make
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Available targets:
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- fuzz_blob_to_kzg_commitment
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- fuzz_compute_blob_kzg_proof
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- fuzz_compute_kzg_proof
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- fuzz_verify_blob_kzg_proof
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- fuzz_verify_blob_kzg_proof_batch
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- fuzz_verify_kzg_proof
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```
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To run a fuzzer, run `make fuzz_<func>` like:
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```
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$ make fuzz_verify_kzg_proof
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[+] Building blst
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+ cc -O2 -fno-builtin -fPIC -Wall -Wextra -Werror -c ./src/server.c
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+ cc -O2 -fno-builtin -fPIC -Wall -Wextra -Werror -c ./build/assembly.S
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+ ar rc libblst.a assembly.o server.o
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[+] Generating corpus
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[+] Compiling verify_kzg_proof fuzzer
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[+] Starting verify_kzg_proof fuzzer
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INFO: Running with entropic power schedule (0xFF, 100).
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INFO: Seed: 855755358
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INFO: Loaded 1 modules (228 inline 8-bit counters): 228 [0x1025a00f8, 0x1025a01dc),
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INFO: Loaded 1 PC tables (228 PCs): 228 [0x1025a01e0,0x1025a1020),
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INFO: 1 files found in ./verify_kzg_proof/corpus
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INFO: seed corpus: files: 1 min: 160b max: 160b total: 160b rss: 28Mb
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#2 pulse ft: 17 exec/s: 1 rss: 29Mb
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#2 INITED cov: 17 ft: 17 corp: 1/160b exec/s: 1 rss: 29Mb
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#4 pulse cov: 17 ft: 17 corp: 1/160b lim: 160 exec/s: 2 rss: 29Mb
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#5 NEW cov: 19 ft: 20 corp: 2/320b lim: 160 exec/s: 2 rss: 29Mb L: 160/160 MS: 3 ChangeASCIIInt-ChangeBit-ChangeBit-
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#7 NEW cov: 20 ft: 21 corp: 3/477b lim: 160 exec/s: 3 rss: 29Mb L: 157/160 MS: 2 ChangeByte-EraseBytes-
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#8 pulse cov: 20 ft: 21 corp: 3/477b lim: 160 exec/s: 4 rss: 29Mb
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#13 NEW cov: 21 ft: 23 corp: 4/637b lim: 160 exec/s: 6 rss: 29Mb L: 160/160 MS: 1 ChangeBit-
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#16 pulse cov: 21 ft: 23 corp: 4/637b lim: 160 exec/s: 8 rss: 29Mb
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...
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```
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There are a few steps:
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* Build the blst library.
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* Generate initial corpora files.
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* Compile the fuzzer.
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* Start the fuzzer.
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Reference [this page](https://llvm.org/docs/LibFuzzer.html#output) for a guide on reading the output.
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To stop the fuzzer, press ctrl-C on your keyboard. It will print something like:
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```
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...
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#65536 pulse cov: 25 ft: 29 corp: 7/961b lim: 160 exec/s: 16384 rss: 29Mb
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#131072 pulse cov: 25 ft: 29 corp: 7/961b lim: 160 exec/s: 18724 rss: 29Mb
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^C==11616== libFuzzer: run interrupted; exiting
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make: [run_fuzz_verify_kzg_proof] Error 72 (ignored)
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```
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If your system has multiple cores, it's easy to run fuzzers on multiple threads.
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Append `THREADS=<n>` where `n` is the number of threads you would like there to
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be. If you wish to use all available CPU cores, specify `-1` as the count.
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```
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$ make fuzz_verify_kzg_proof THREADS=4
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[+] Starting verify_kzg_proof fuzzer
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./verify_kzg_proof/fuzz -artifact_prefix=./verify_kzg_proof/ -max_len=160 ./verify_kzg_proof/corpus >fuzz-0.log 2>&1
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./verify_kzg_proof/fuzz -artifact_prefix=./verify_kzg_proof/ -max_len=160 ./verify_kzg_proof/corpus >fuzz-2.log 2>&1
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./verify_kzg_proof/fuzz -artifact_prefix=./verify_kzg_proof/ -max_len=160 ./verify_kzg_proof/corpus >fuzz-1.log 2>&1
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./verify_kzg_proof/fuzz -artifact_prefix=./verify_kzg_proof/ -max_len=160 ./verify_kzg_proof/corpus >fuzz-3.log 2>&1
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```
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When you press ctrl-C it will stop all the fuzzers and print their output to
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your console sequentially. You will most likely need to scroll up to see their
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outputs.
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When operating in parallel (threads) the fuzzers use a shared corpus and are
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intelligent enough to learn from other threads that have progressed further.
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When you see a line that starts with "RELOAD" that fuzzer process is updating
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its corpus with findings from other threads.
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### Findings
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If there is a crash or timeout, the fuzzer will write a file to the target
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directory containing the input data associated with that crash/timeout. If this
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happens, please report the finding via an issue on GitHub.
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