| # Tint Fuzzers |
| |
| Tint currently has two fuzzer target executables: [`tint_wgsl_fuzzer`](#tint_wgsl_fuzzer) which takes WGSL source code as input and [`tint_ir_fuzzer`](#tint_ir_fuzzer) which takes a protobuf binary file as input. |
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| Both fuzzers are implemented using [libFuzzer](https://llvm.org/docs/LibFuzzer.html), and are automatically and continuously run by Chromium's ClusterFuzz infrastructure. [Fuzzer targets are automatically found via `gn refs`](https://chromium.googlesource.com/chromium/src/+/HEAD/testing/libfuzzer/libFuzzer_integration.md). See [`tint.gni`](../../src/tint/tint.gni) for the core fuzzer target rules. |
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| Tint's fuzzers are implemented as functions registered with the macros: |
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| - [`TINT_WGSL_PROGRAM_FUZZER()`](#registering-a-new-tintprogram-fuzzer) registers a fuzzer function that is handed a `tint::Program`. |
| - [`TINT_IR_MODULE_FUZZER()`](#registering-a-new-tintcoreirmodule-fuzzer) registers a fuzzer function that is handed a `tint::core::ir::Module`. |
| |
| ## Building |
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| The fuzzer targets can be build with either CMake or GN: |
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| - CMake: Define `TINT_BUILD_FUZZERS=1` (pass `-DTINT_BUILD_FUZZERS=1` to `CMake`) |
| - GN: Define `use_libfuzzer = true` in `args.gn`. |
| |
| ## Running fuzzers |
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| ### Local fuzzing |
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| The [`tint_wgsl_fuzzer`](#tint_wgsl_fuzzer) and [`tint_ir_fuzzer`](#tint_ir_fuzzer) executables accept the [standard `libFuzzer` command line arguments](https://llvm.org/docs/LibFuzzer.html#options) with [extended command line arguments](#extended-command-line-arguments) described below. |
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| There's also a helper tool to run the fuzzers locally: |
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| - To run the local fuzzers across the full number of CPU threads available on the system, seeded with the corpus in [`test/tint`](../../test/tint), and using the dictionary in `src/tint/cmd/fuzz/wgsl/dictionary.txt` run: |
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| `tools/run fuzz` |
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| - To check that all the test files in the corpus directory, [`test/tint`](../../test/tint) by default, pass the fuzzers without error and then exit, run: |
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| `tools/run fuzz --check` |
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| Note: This is run by Dawn's CQ presubmit to check that fuzzers aren't accidentally broken. |
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| - To run the local fuzzers using the same corpus used by ClusterFuzz: |
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| `tools/run fuzz -corpus out/libfuzz/gen/fuzzers/wgsl_corpus` |
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| Note that this corpus directory is generated when building the GN target `tint_generate_wgsl_corpus`. |
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| ### Generating the corpus |
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| Generate the `tint_wgsl_fuzzer` corpus using the `tint_generate_wgsl_corpus` GN target, which produces a corpus in `<build_dir>/gen/fuzzers/wgsl_corpus`. Pass in the path to the corpus directory as an argument to the fuzzer executable to use it. It's also a good idea to pass in the dictionary with `-dict=src/tint/cmd/fuzz/wgsl/dictionary.txt`: |
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| ```bash |
| autoninja -C out/libfuzz tint_generate_wgsl_corpus |
| out/libfuzz/tint_wgsl_fuzzer.exe -dict=src/tint/cmd/fuzz/wgsl/dictionary.txt out/libfuzz/gen/fuzzers/wgsl_corpus |
| ``` |
| |
| Similarly, the `tint_ir_fuzzer` corpus can be generated using the `tint_generate_ir_corpus` GN target, producing the corpus in `<build_dir>/gen/fuzzers/ir_corpus`. For the IR fuzzer, we don't pass in the dictionary, since we are using lpm for mutating (the proto file effectively defines the dictionary): |
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| ```bash |
| autoninja -C out/libfuzz tint_generate_ir_corpus |
| out/libfuzz/tint_ir_fuzzer.exe out/libfuzz/gen/fuzzers/ir_corpus |
| ``` |
| |
| ## Writing fuzzers |
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| ### Registering a new `tint::Program` fuzzer |
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| 1. Create a new source file with a `_fuzz.cc` suffix. |
| 2. `#include "src/tint/cmd/fuzz/wgsl/fuzz.h"` |
| 3. Define a function in a (possibly nested) anonymous namespace with one of the signatures: |
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| - `void MyFuzzer(const tint::Program& program /*, ...additional fuzzed parameters... */) {` |
| - `void MyFuzzer(const tint::Program& program, const tint::fuzz::wgsl::Context& context /*, ...additional fuzzed parameters... */) {` |
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| The optional `context` parameter holds information about the `Program` and the environment used to run the fuzzers. \ |
| [Note: Any number of additional fuzzer-populated parameters can be appended to the function signature.](#additional-fuzzer-data) |
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| 4. Implement your fuzzer function, using `TINT_ICE()` to catch invalid state. Return early if the fuzzer cannot handle the input. |
| 5. At the bottom of the file, in the global namespace, register the fuzzer with: `TINT_WGSL_PROGRAM_FUZZER(MyFuzzer);` |
| 6. Use `tools/run gen build` to generate the build files for this new fuzzer. |
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| Example: |
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| ```c++ |
| #include "src/tint/cmd/fuzz/wgsl/fuzz.h" |
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| namespace tint::my_namespace { |
| namespace { |
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| bool CanRun(const tint::Program& program) { |
| if (program.AST().HasOverrides()) { |
| return false; // Overrides are not supported. |
| } |
| return true; |
| } |
| |
| void MyWGSLFuzzer(const tint::Program& program, bool a_fuzzer_provided_value) { |
| if (!CanRun(program)) { |
| return; |
| } |
| |
| // Check something with program. |
| } |
| |
| } // namespace |
| } // namespace tint::my_namespace |
| |
| TINT_WGSL_PROGRAM_FUZZER(tint::my_namespace::MyWGSLFuzzer); |
| ``` |
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| ### Registering a new `tint::core::ir::Module` fuzzer |
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| 1. Create a new source file with a `_fuzz.cc` suffix. |
| 2. `#include "src/tint/cmd/fuzz/ir/fuzz.h"` |
| 3. Define a function in a (possibly nested) anonymous namespace with the signature: |
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| - `void MyFuzzer(core::ir::Module& module /*, ...additional fuzzed parameters... */) {` |
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| [Note: Any number of additional fuzzer-populated parameters can be appended to the function signature.](#additional-fuzzer-data) |
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| 4. Implement your fuzzer function, using `TINT_ICE()` to catch invalid state. Return early if the fuzzer cannot handle the input. |
| 5. At the bottom of the file, in the global namespace, register the fuzzer with: `TINT_IR_MODULE_FUZZER(MyFuzzer);` |
| 6. Use `tools/run gen build` to generate the build files for this new fuzzer. |
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| Example: |
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| ```c++ |
| #include "src/tint/cmd/fuzz/ir/fuzz.h" |
| |
| namespace tint::my_namespace { |
| namespace { |
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| void MyIRFuzzer(core::ir::Module& module) { |
| // Do something interesting with module. |
| } |
| |
| } // namespace |
| } // namespace tint::my_namespace |
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| TINT_IR_MODULE_FUZZER(tint::my_namespace::MyIRFuzzer); |
| ``` |
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| ### Additional fuzzer data |
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| WGSL and IR fuzzer functions can also declare any number of additional parameters, which will be populated with fuzzer provided data. These additional parameters must come at the end of the signatures described above, and can be of the following types: |
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| - Any integer, float or bool type. |
| - Any structure reflected with `TINT_REFLECT`. Note: It's recommended to use a `const` reference, for these to avoid pass-by-value overheads. |
| - Any enum reflected with `TINT_REFLECT_ENUM_RANGE`. |
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| ## Executable targets |
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| Tint has two fuzzer executable targets: |
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| ### `tint_wgsl_fuzzer` |
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| `tint_wgsl_fuzzer` [accepts WGSL textual input](https://llvm.org/docs/LibFuzzer.html#options) and parses line comments (`//`) as a base-64 binary encoded data stream for the [additional fuzzer parameters](additional-fuzzer-data). |
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| The entry point for the fuzzer lives at [`src/tint/cmd/fuzz/wgsl/main_fuzz.cc`](../../src/tint/cmd/fuzz/wgsl/main_fuzz.cc). |
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| #### Extended command line arguments |
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| On top of the [standard `libFuzzer` command line arguments](https://llvm.org/docs/LibFuzzer.html#options), the fuzzers support the following extended command line arguments: |
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| - `--help`: lists the command line arguments. |
| - `--filter=<name>`: only runs the fuzzer functions that contain the given string in its name. |
| - `--concurrent`: each of the fuzzer functions will be run on a separate, concurrent thread. This potentially offers performance improvements, and also tests for concurrent execution. |
| - `--verbose` : prints verbose information about what the fuzzer is doing. |
| - `--dump` : prints shader source, including input WGSL, and genreated HLSL, MSL, and GLSL. |
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| #### Behavior |
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| The `tint_wgsl_fuzzer` will do the following: |
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| - Base-64 decode the line comments data from the WGSL source, used to populate the [additional fuzzer parameters](additional-fuzzer-data). |
| - Parse and resolve the WGSL input, and will early-return if there are any parser errors. |
| - Invoke each of the fuzzer functions registered with a call to `TINT_WGSL_PROGRAM_FUZZER()` |
| - Automatically convert the `Program` to an IR module and run the function for each function registered with `TINT_IR_MODULE_FUZZER()`. Note: The `Program` is converted to an IR module for each registered IR fuzzer as the module is mutable. |
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| ### `tint_ir_fuzzer` |
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| TODO: Document when landed. |
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| ## Debugging |
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| To debug a specific registered fuzzer function, one strategy is to add a `TINT_ICE` call at the top of the function, and then run the fuzzer with `-filter <name>` to have it only run that specific fuzzer. When the function is called, the libfuzzer harness will emit a crash file that can be used as input on subsequent runs. Remove the `TINT_ICE` and run the fuzzer again using this crash file. |
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| For example, if we wish to debug `tint::msl::writer::IRFuzzer`, we would first insert a `TINT_ICE` at the top: |
| |
| ```c++ |
| Result<SuccessType> IRFuzzer(core::ir::Module& module, |
| const fuzz::ir::Context& context, |
| Options options) { |
| TINT_ICE() << "Crash"; |
| // Comment out the rest of the body to avoid unreachable code warnings |
| } |
| ``` |
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| Build and run the fuzzer, filtering in this function: |
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| ```bash |
| autoninja -C out/libfuzz tint_wgsl_fuzzer |
| out/libfuzz/tint_wgsl_fuzzer -filter=tint::msl::writer::IRFuzzer |
| ``` |
| |
| It can take a little while before libfuzzer generates a valid input WGSL, but eventually it will call into the function and crash on the ICE: |
| |
| ``` |
| ... |
| #71607 NEW cov: 3633 ft: 8316 corp: 1045/8248b lim: 25 exec/s: 2469 rss: 158Mb L: 8/25 MS: 2 ShuffleBytes-PersAutoDict- DE: "true"- |
| #71669 NEW cov: 3633 ft: 8317 corp: 1046/8266b lim: 25 exec/s: 2471 rss: 158Mb L: 18/25 MS: 2 CMP-ChangeByte- DE: "if"- |
| #71697 REDUCE cov: 3633 ft: 8317 corp: 1046/8264b lim: 25 exec/s: 2472 rss: 158Mb L: 6/25 MS: 3 PersAutoDict-ChangeBit-EraseBytes- DE: "\001\002"- |
| ICE while running fuzzer: 'tint::msl::writer::IRFuzzer' |
| ..\..\src\tint\lang\msl\writer\writer_fuzz.cc:63 internal compiler error: Crash |
| ==25204== ERROR: libFuzzer: deadly signal |
| NOTE: libFuzzer has rudimentary signal handlers. |
| Combine libFuzzer with AddressSanitizer or similar for better crash reports. |
| SUMMARY: libFuzzer: deadly signal |
| MS: 1 PersAutoDict- DE: "or"-; base unit: b34d87c378ebbbfbfd475303dcc75d1d1b2a7c7a |
| 0x2f,0x2f,0x33,0x33,0x33,0x33,0x6f,0x72,0x33,0x33,0x33,0x33,0x33,0x33,0x33,0x33,0x33,0x33,0x2a,0x2a,0x30,0x32, |
| //3333or3333333333**02 |
| artifact_prefix='./'; Test unit written to ./crash-21563a85afd5322d9e17c1c43fd3d4029778d6e7 |
| Base64: Ly8zMzMzb3IzMzMzMzMzMzMzKiowMg== |
| ``` |
| |
| Note that the second to last line specifies that the input test was written to a file. Now we can remove the `TINT_ICE` and run the fuzzer with just this file as input: |
| |
| ```bash |
| out/libfuzz/tint_wgsl_fuzzer ./crash-21563a85afd5322d9e17c1c43fd3d4029778d6e7 |
| ``` |