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Update the wire-based fuzzers to always assume an injected error

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This also removes the ability for the fuzzer to perform error
injection to generate testcases. The preferred method is to
use one of the Dawn test binaries to produce the trace directly.

Bug: dawn:629
Change-Id: If7295f9e6da5618be8f44e9301aa12dc56fcdfef
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/40301
Reviewed-by: Corentin Wallez <cwallez@chromium.org>
Commit-Queue: Austin Eng <enga@chromium.org>
This commit is contained in:
Austin Eng
2021-03-23 16:47:50 +00:00
committed by Commit Bot service account
parent 94b8b7408e
commit be621bd0e6
3 changed files with 15 additions and 175 deletions
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docs/fuzzing.md
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@@ -8,19 +8,11 @@ The `dawn_wire_server_and_frontend_fuzzer` sets up Dawn using the Null backend,
The `dawn_wire_server_and_vulkan_backend_fuzzer` is like `dawn_wire_server_and_frontend_fuzzer` but it runs using a Vulkan CPU backend such as Swiftshader. This fuzzer supports error injection by using the first bytes of the fuzzing input as a Vulkan call index for which to mock a failure.
## Updating the Seed Corpus
## Automatic Seed Corpus Generation
Using a seed corpus significantly improves the efficiency of fuzzing. Dawn's fuzzers use interesting testcases discovered in previous fuzzing runs to seed future runs. Fuzzing can be further improved by using Dawn tests as a example of API usage which allows the fuzzer to quickly discover and use new API entrypoints and usage patterns.
The script [update_fuzzer_seed_corpus.sh](../scripts/update_fuzzer_seed_corpus.sh) can be used to capture a trace while running Dawn tests, and upload it to the existing fuzzer seed corpus. It does the following steps:
1. Builds the provided test and fuzzer targets.
2. Runs the provided test target with `--use-wire --wire-trace-dir=tmp_dir1 [additional_test_args]` to dump traces of the tests.
3. Generates one variant of each trace for every possible error index, by running the fuzzer target with `--injected-error-testcase-dir=tmp_dir2 ...`.
4. Minimizes all testcases by running the fuzzer target with `-merge=1 tmp_dir3 tmp_dir1 tmp_dir2`.
Dawn has a CI builder [cron-linux-clang-rel-x64](https://ci.chromium.org/p/dawn/builders/ci/cron-linux-clang-rel-x64) which runs on a periodic schedule. This bot runs the `dawn_end2end_tests` and `dawn_unittests` using the wire and writes out traces of the commands. This can manually be done by running: `<test_binary> --use-wire --wire-trace-dir=tmp_dir`. The output directory will contain one trace for each test, where the traces are prepended with `0xFFFFFFFFFFFFFFFF`. The header is the callsite index at which the error injector should inject an error. If the fuzzer doesn't support error injection it will skip the header. [cron-linux-clang-rel-x64] then hashes the output files to produce unique names and uploads them to the fuzzer corpus directories.
Please see the `dawn.py`[https://source.chromium.org/chromium/chromium/tools/build/+/master:recipes/recipes/dawn.py] recipe for specific details.
To run the script:
1. You must be in a Chromium checkout using the GN arg `use_libfuzzer=true`
2. Run `./third_party/dawn/scripts/update_fuzzer_seed_corpus.sh <out_dir> <fuzzer> <test> [additional_test_args]`.
Example: `./third_party/dawn/scripts/update_fuzzer_seed_corpus.sh out/fuzz dawn_wire_server_and_vulkan_backend_fuzzer dawn_end2end_tests --gtest_filter=*Vulkan`
3. The script will print instructions for testing, and then uploading new inputs. Please, only upload inputs after testing the fuzzer with new inputs, and verifying there is a meaningful change in coverage. Uploading requires [gcloud](https://g3doc.corp.google.com/cloud/sdk/g3doc/index.md?cl=head) to be logged in with @google.com credentials: `gcloud auth login`.
Regenerating the seed corpus keeps it up to date when Dawn's API or wire protocol changes.