-# I Can Haz Fuzz?
+Fuzzing OpenSSL
+===============
+
+OpenSSL can use either LibFuzzer or AFL to do fuzzing.
LibFuzzer
-=========
+---------
-Or, how to fuzz OpenSSL with [libfuzzer](http://llvm.org/docs/LibFuzzer.html).
+How to fuzz OpenSSL with [libfuzzer](http://llvm.org/docs/LibFuzzer.html),
+starting from a vanilla+OpenSSH server Ubuntu install.
-Starting from a vanilla+OpenSSH server Ubuntu install.
+With `clang` from a package manager
+-----------------------------------
-Use Chrome's handy recent build of clang. Older versions may also work.
+Install `clang`, which [ships with `libfuzzer`](http://llvm.org/docs/LibFuzzer.html#fuzzer-usage)
+since version 6.0:
- $ sudo apt-get install git
- $ mkdir git-work
- $ git clone https://chromium.googlesource.com/chromium/src/tools/clang
- $ clang/scripts/update.py
+ sudo apt-get install clang
-You may want to git pull and re-run the update from time to time.
+Configure `openssl` for fuzzing. For now, you'll still need to pass in the path
+to the `libFuzzer` library file while configuring; this is represented as
+`$PATH_TO_LIBFUZZER` below. A typical value would be
+`/usr/lib/llvm-7/lib/clang/7.0.1/lib/linux/libclang_rt.fuzzer-x86_64.a`.
-Update your path:
+ CC=clang ./config enable-fuzz-libfuzzer \
+ --with-fuzzer-lib=$PATH_TO_LIBFUZZER \
+ -DPEDANTIC enable-asan enable-ubsan no-shared \
+ -DFUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION \
+ -fsanitize=fuzzer-no-link \
+ enable-ec_nistp_64_gcc_128 -fno-sanitize=alignment \
+ enable-weak-ssl-ciphers enable-rc5 enable-md2 \
+ enable-ssl3 enable-ssl3-method enable-nextprotoneg \
+ --debug
- $ PATH=~/third_party/llvm-build/Release+Asserts/bin/:$PATH
+Compile:
-Get and build libFuzzer (there is a git mirror at
-https://github.com/llvm-mirror/llvm/tree/master/lib/Fuzzer if you prefer):
+ sudo apt-get install make
+ make clean
+ LDCMD=clang++ make -j4
- $ cd
- $ sudo apt-get install subversion
- $ mkdir svn-work
- $ cd svn-work
- $ svn co http://llvm.org/svn/llvm-project/llvm/trunk/lib/Fuzzer
- $ cd Fuzzer
- $ clang++ -c -g -O2 -std=c++11 *.cpp
- $ ar r libFuzzer.a *.o
- $ ranlib libFuzzer.a
+Finally, perform the actual fuzzing:
-Configure for fuzzing:
+ fuzz/helper.py $FUZZER
+
+where $FUZZER is one of the executables in `fuzz/`.
+It will run until you stop it.
+
+If you get a crash, you should find a corresponding input file in
+`fuzz/corpora/$FUZZER-crash/`.
+
+With `clang` from source/pre-built binaries
+-------------------------------------------
+
+You may also wish to use a pre-built binary from the [LLVM Download
+site](http://releases.llvm.org/download.html), or to [build `clang` from
+source](https://clang.llvm.org/get_started.html). After adding `clang` to your
+path and locating the `libfuzzer` library file, the procedure for configuring
+fuzzing is the same, except that you also need to specify
+a `--with-fuzzer-include` option, which should be the parent directory of the
+prebuilt fuzzer library. This is represented as `$PATH_TO_LIBFUZZER_DIR` below.
- $ CC=clang ./config enable-fuzz-libfuzzer \
- --with-fuzzer-include=../../svn-work/Fuzzer \
- --with-fuzzer-lib=../../svn-work/Fuzzer/libFuzzer \
+ CC=clang ./config enable-fuzz-libfuzzer \
+ --with-fuzzer-include=$PATH_TO_LIBFUZZER_DIR \
+ --with-fuzzer-lib=$PATH_TO_LIBFUZZER \
-DPEDANTIC enable-asan enable-ubsan no-shared \
-DFUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION \
- -fsanitize-coverage=edge,indirect-calls,8bit-counters \
- enable-ec_nistp_64_gcc_128 -fno-sanitize=alignment enable-tls1_3 \
+ -fsanitize=fuzzer-no-link \
+ enable-ec_nistp_64_gcc_128 -fno-sanitize=alignment \
enable-weak-ssl-ciphers enable-rc5 enable-md2 \
enable-ssl3 enable-ssl3-method enable-nextprotoneg \
--debug
- $ sudo apt-get install make
- $ LDCMD=clang++ make -j
- $ fuzz/helper.py $FUZZER
-
-Where $FUZZER is one of the executables in `fuzz/`.
-
-If you get a crash, you should find a corresponding input file in
-`fuzz/corpora/$FUZZER-crash/`.
AFL
-===
+---
+
+This is an alternative to using LibFuzzer.
Configure for fuzzing:
- $ sudo apt-get install afl-clang
- $ CC=afl-clang-fast ./config enable-fuzz-afl no-shared -DPEDANTIC \
- enable-tls1_3 enable-weak-ssl-ciphers enable-rc5 enable-md2 \
- enable-ssl3 enable-ssl3-method enable-nextprotoneg \
+ sudo apt-get install afl-clang
+ CC=afl-clang-fast ./config enable-fuzz-afl no-shared no-module \
+ -DPEDANTIC enable-tls1_3 enable-weak-ssl-ciphers enable-rc5 \
+ enable-md2 enable-ssl3 enable-ssl3-method enable-nextprotoneg \
enable-ec_nistp_64_gcc_128 -fno-sanitize=alignment \
--debug
- $ make
+ make clean
+ make
The following options can also be enabled: enable-asan, enable-ubsan, enable-msan
Run one of the fuzzers:
- $ afl-fuzz -i fuzz/corpora/$FUZZER -o fuzz/corpora/$FUZZER/out fuzz/$FUZZER
+ afl-fuzz -i fuzz/corpora/$FUZZER -o fuzz/corpora/$FUZZER/out fuzz/$FUZZER
Where $FUZZER is one of the executables in `fuzz/`.
Reproducing issues
-==================
+------------------
If a fuzzer generates a reproducible error, you can reproduce the problem using
the fuzz/*-test binaries and the file generated by the fuzzer. They binaries
To reproduce the crash you can run:
- $ fuzz/$FUZZER-test $file
+ fuzz/$FUZZER-test $file
Random numbers
-==============
+--------------
The client and server fuzzer normally generate random numbers as part of the TLS
connection setup. This results in the coverage of the fuzzing corpus changing
emulated by the file, can be generated for that client hello.
Coverage changes
-================
+----------------
Since the corpus depends on the default behaviour of the client and the server,
changes in what they send by default will have an impact on the coverage. The
corpus will need to be updated in that case.
+Updating the corpus
+-------------------
+
+The client and server corpus is generated with multiple config options:
+
+- The options as documented above
+- Without enable-ec_nistp_64_gcc_128 and without --debug
+- With no-asm
+- Using 32 bit
+- A default config, plus options needed to generate the fuzzer.
+
+The libfuzzer merge option is used to add the additional coverage
+from each config to the minimal set.
+
+Minimizing the corpus
+---------------------
+
+When you have gathered corpus data from more than one fuzzer run
+or for any other reason want to to minimize the data
+in some corpus subdirectory `fuzz/corpora/DIR` this can be done as follows:
+
+ mkdir fuzz/corpora/NEWDIR
+ fuzz/$FUZZER -merge=1 fuzz/corpora/NEWDIR fuzz/corpora/DIR
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