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Move lib/Fuzzer docs from a README.txt to a proper .rst file.
Summary: Move lib/Fuzzer docs from a README.txt to a proper .rst file. This change does not add any content, just formatting. Test Plan: n/a Reviewers: samsonov Reviewed By: samsonov Subscribers: llvm-commits Differential Revision: http://reviews.llvm.org/D8710 llvm-svn: 233638
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Kostya Serebryany
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docs/LibFuzzer.rst
Normal file
128
docs/LibFuzzer.rst
Normal file
@ -0,0 +1,128 @@
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LibFuzzer -- a library for coverage-guided fuzz testing.
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========================================================
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This library is intended primarily for in-process coverage-guided fuzz testing
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(fuzzing) of other libraries. The typical workflow looks like this:
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* Build the Fuzzer library as a static archive (or just a set of .o files).
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Note that the Fuzzer contains the main() function.
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Preferably do *not* use sanitizers while building the Fuzzer.
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* Build the library you are going to test with -fsanitize-coverage=[234]
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and one of the sanitizers. We recommend to build the library in several
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different modes (e.g. asan, msan, lsan, ubsan, etc) and even using different
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optimizations options (e.g. -O0, -O1, -O2) to diversify testing.
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* Build a test driver using the same options as the library.
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The test driver is a C/C++ file containing interesting calls to the library
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inside a single function ``extern "C" void TestOneInput(const uint8_t *Data, size_t Size);``
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* Link the Fuzzer, the library and the driver together into an executable
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using the same sanitizer options as for the library.
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* Collect the initial corpus of inputs for the
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fuzzer (a directory with test inputs, one file per input).
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The better your inputs are the faster you will find something interesting.
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Also try to keep your inputs small, otherwise the Fuzzer will run too slow.
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* Run the fuzzer with the test corpus. As new interesting test cases are
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discovered they will be added to the corpus. If a bug is discovered by
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the sanitizer (asan, etc) it will be reported as usual and the reproducer
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will be written to disk.
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Each Fuzzer process is single-threaded (unless the library starts its own
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threads). You can run the Fuzzer on the same corpus in multiple processes.
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in parallel. For run-time options run the Fuzzer binary with '-help=1'.
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The Fuzzer is similar in concept to AFL (http://lcamtuf.coredump.cx/afl/),
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but uses in-process Fuzzing, which is more fragile, more restrictive, but
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potentially much faster as it has no overhead for process start-up.
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It uses LLVM's "Sanitizer Coverage" instrumentation to get in-process
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coverage-feedback https://code.google.com/p/address-sanitizer/wiki/AsanCoverage
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The code resides in the LLVM repository and is (or will be) used by various
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parts of LLVM, but the Fuzzer itself does not (and should not) depend on any
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part of LLVM and can be used for other projects. Ideally, the Fuzzer's code
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should not have any external dependencies. Right now it uses STL, which may need
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to be fixed later. See also FAQ below.
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Examples of usage in LLVM
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=========================
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clang-format-fuzzer
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-------------------
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The inputs are random pieces of C++-like text.
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Build (make sure to use fresh clang as the host compiler)::
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cmake -GNinja -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++ -DLLVM_USE_SANITIZER=Address -DLLVM_USE_SANITIZE_COVERAGE=YES -DCMAKE_BUILD_TYPE=Release /path/to/llvm
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ninja clang-format-fuzzer
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mkdir CORPUS_DIR
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./bin/clang-format-fuzzer CORPUS_DIR
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Optionally build other kinds of binaries (asan+Debug, msan, ubsan, etc).
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TODO: commit the pre-fuzzed corpus to svn (?).
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Toy example
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-------------------
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See lib/Fuzzer/test/SimpleTest.cpp.
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A simple function that does something interesting if it receives bytes "Hi!"::
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# Build the Fuzzer with asan:
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clang++ -std=c++11 -fsanitize=address -fsanitize-coverage=3 -O1 -g Fuzzer*.cpp test/SimpleTest.cpp
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# Run the fuzzer with no corpus (assuming on empty input)
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./a.out
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FAQ
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=========================
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Q. Why Fuzzer does not use any of the LLVM support?
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---------------------------------------------------
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There are two reasons.
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First, we want this library to be used outside of the LLVM w/o users having to
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build the rest of LLVM. This may sound unconvincing for many LLVM folks,
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but in practice the need for building the whole LLVM frightens many potential
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users -- and we want more users to use this code.
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Second, there is a subtle technical reason not to rely on the rest of LLVM, or
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any other large body of code (maybe not even STL). When coverage instrumentation
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is enabled, it will also instrument the LLVM support code which will blow up the
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coverage set of the process (since the fuzzer is in-process). In other words, by
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using more external dependencies we will slow down the fuzzer while the main
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reason for it to exist is extreme speed.
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Q. What about Windows then? The Fuzzer contains code that does not build on Windows.
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------------------------------------------------------------------------------------
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The sanitizer coverage support does not work on Windows either as of 01/2015.
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Once it's there, we'll need to re-implement OS-specific parts (I/O, signals).
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Q. When this Fuzzer is not a good solution for a problem?
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---------------------------------------------------------
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* If the test inputs are validated by the target library and the validator
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asserts/crashes on invalid inputs, the in-process fuzzer is not applicable
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(we could use fork() w/o exec, but it comes with extra overhead).
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* Bugs in the target library may accumulate w/o being detected. E.g. a memory
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corruption that goes undetected at first and then leads to a crash while
|
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testing another input. This is why it is highly recommended to run this
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in-process fuzzer with all sanitizers to detect most bugs on the spot.
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* It is harder to protect the in-process fuzzer from excessive memory
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consumption and infinite loops in the target library (still possible).
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* The target library should not have significant global state that is not
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reset between the runs.
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* Many interesting target libs are not designed in a way that supports
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the in-process fuzzer interface (e.g. require a file path instead of a
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byte array).
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* If a single test run takes a considerable fraction of a second (or
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more) the speed benefit from the in-process fuzzer is negligible.
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* If the target library runs persistent threads (that outlive
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execution of one test) the fuzzing results will be unreliable.
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Q. So, what exactly this Fuzzer is good for?
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--------------------------------------------
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This Fuzzer might be a good choice for testing libraries that have relatively
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small inputs, each input takes < 1ms to run, and the library code is not expected
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to crash on invalid inputs.
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Examples: regular expression matchers, text or binary format parsers.
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@ -177,6 +177,7 @@ For developers of applications which use LLVM as a library.
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HowToSetUpLLVMStyleRTTI
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ProgrammersManual
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Extensions
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LibFuzzer
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:doc:`LLVM Language Reference Manual <LangRef>`
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Defines the LLVM intermediate representation and the assembly form of the
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@ -218,6 +219,9 @@ For developers of applications which use LLVM as a library.
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:doc:`CompilerWriterInfo`
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A list of helpful links for compiler writers.
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:doc:`LibFuzzer`
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A library for writing in-process guided fuzzers.
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Subsystem Documentation
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=======================
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@ -1,112 +1,2 @@
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===============================
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Fuzzer -- a library for coverage-guided fuzz testing.
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===============================
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Move to http://llvm.org/docs/LibFuzzer.html
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This library is intended primarily for in-process coverage-guided fuzz testing
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(fuzzing) of other libraries. The typical workflow looks like this:
|
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|
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* Build the Fuzzer library as a static archive (or just a set of .o files).
|
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Note that the Fuzzer contains the main() function.
|
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Preferably do *not* use sanitizers while building the Fuzzer.
|
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* Build the library you are going to test with -fsanitize-coverage=[234]
|
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and one of the sanitizers. We recommend to build the library in several
|
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different modes (e.g. asan, msan, lsan, ubsan, etc) and even using different
|
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optimizations options (e.g. -O0, -O1, -O2) to diversify testing.
|
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* Build a test driver using the same options as the library.
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The test driver is a C/C++ file containing interesting calls to the library
|
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inside a single function:
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extern "C" void TestOneInput(const uint8_t *Data, size_t Size);
|
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* Link the Fuzzer, the library and the driver together into an executable
|
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using the same sanitizer options as for the library.
|
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* Collect the initial corpus of inputs for the
|
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fuzzer (a directory with test inputs, one file per input).
|
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The better your inputs are the faster you will find something interesting.
|
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Also try to keep your inputs small, otherwise the Fuzzer will run too slow.
|
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* Run the fuzzer with the test corpus. As new interesting test cases are
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discovered they will be added to the corpus. If a bug is discovered by
|
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the sanitizer (asan, etc) it will be reported as usual and the reproducer
|
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will be written to disk.
|
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Each Fuzzer process is single-threaded (unless the library starts its own
|
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threads). You can run the Fuzzer on the same corpus in multiple processes.
|
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in parallel. For run-time options run the Fuzzer binary with '-help=1'.
|
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|
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|
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The Fuzzer is similar in concept to AFL (http://lcamtuf.coredump.cx/afl/),
|
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but uses in-process Fuzzing, which is more fragile, more restrictive, but
|
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potentially much faster as it has no overhead for process start-up.
|
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It uses LLVM's "Sanitizer Coverage" instrumentation to get in-process
|
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coverage-feedback https://code.google.com/p/address-sanitizer/wiki/AsanCoverage
|
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|
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The code resides in the LLVM repository and is (or will be) used by various
|
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parts of LLVM, but the Fuzzer itself does not (and should not) depend on any
|
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part of LLVM and can be used for other projects. Ideally, the Fuzzer's code
|
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should not have any external dependencies. Right now it uses STL, which may need
|
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to be fixed later. See also F.A.Q. below.
|
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|
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Examples of usage in LLVM:
|
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* clang-format-fuzzer. The inputs are random pieces of C++-like text.
|
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* Build (make sure to use fresh clang as the host compiler):
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cmake -GNinja -DCMAKE_C_COMPILER=clang -DCMAKE_CXX_COMPILER=clang++ \
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-DLLVM_USE_SANITIZER=Address -DLLVM_USE_SANITIZE_COVERAGE=YES \
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/path/to/llvm -DCMAKE_BUILD_TYPE=Release
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ninja clang-format-fuzzer
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* Optionally build other kinds of binaries (asan+Debug, msan, ubsan, etc)
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* TODO: commit the pre-fuzzed corpus to svn (?).
|
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* Run:
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clang-format-fuzzer CORPUS_DIR
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|
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Toy example (see SimpleTest.cpp):
|
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a simple function that does something interesting if it receives bytes "Hi!".
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# Build the Fuzzer with asan:
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% clang++ -std=c++11 -fsanitize=address -fsanitize-coverage=3 -O1 -g \
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Fuzzer*.cpp test/SimpleTest.cpp
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# Run the fuzzer with no corpus (assuming on empty input)
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% ./a.out
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===============================================================================
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F.A.Q.
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Q. Why Fuzzer does not use any of the LLVM support?
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A. There are two reasons.
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First, we want this library to be used outside of the LLVM w/o users having to
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build the rest of LLVM. This may sound unconvincing for many LLVM folks,
|
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but in practice the need for building the whole LLVM frightens many potential
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users -- and we want more users to use this code.
|
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Second, there is a subtle technical reason not to rely on the rest of LLVM, or
|
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any other large body of code (maybe not even STL). When coverage instrumentation
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is enabled, it will also instrument the LLVM support code which will blow up the
|
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coverage set of the process (since the fuzzer is in-process). In other words, by
|
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using more external dependencies we will slow down the fuzzer while the main
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reason for it to exist is extreme speed.
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Q. What about Windows then? The Fuzzer contains code that does not build on
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Windows.
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A. The sanitizer coverage support does not work on Windows either as of 01/2015.
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Once it's there, we'll need to re-implement OS-specific parts (I/O, signals).
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Q. When this Fuzzer is not a good solution for a problem?
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A.
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* If the test inputs are validated by the target library and the validator
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asserts/crashes on invalid inputs, the in-process fuzzer is not applicable
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(we could use fork() w/o exec, but it comes with extra overhead).
|
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* Bugs in the target library may accumulate w/o being detected. E.g. a memory
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corruption that goes undetected at first and then leads to a crash while
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testing another input. This is why it is highly recommended to run this
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in-process fuzzer with all sanitizers to detect most bugs on the spot.
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* It is harder to protect the in-process fuzzer from excessive memory
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consumption and infinite loops in the target library (still possible).
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* The target library should not have significant global state that is not
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reset between the runs.
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* Many interesting target libs are not designed in a way that supports
|
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the in-process fuzzer interface (e.g. require a file path instead of a
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byte array).
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* If a single test run takes a considerable fraction of a second (or
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more) the speed benefit from the in-process fuzzer is negligible.
|
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* If the target library runs persistent threads (that outlive
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execution of one test) the fuzzing results will be unreliable.
|
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|
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Q. So, what exactly this Fuzzer is good for?
|
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A. This Fuzzer might be a good choice for testing libraries that have relatively
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small inputs, each input takes < 1ms to run, and the library code is not expected
|
||||
to crash on invalid inputs.
|
||||
Examples: regular expression matchers, text or binary format parsers.
|
||||
|
||||
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