diff options
author | Brian Chen <brian.chxn@gmail.com> | 2019-05-07 04:05:44 -0400 |
---|---|---|
committer | Kurt Roeckx <kurt@roeckx.be> | 2019-09-18 22:19:24 +0200 |
commit | 639b53ecd82648fbb66a2ab7dabece7f15a1f730 (patch) | |
tree | 3763b421564d03168c5d41303005895d8ce35061 /fuzz | |
parent | a74b2eda2fcc386e85c6f859729631b0642c4ee6 (diff) | |
download | openssl-639b53ecd82648fbb66a2ab7dabece7f15a1f730.tar.gz |
Update fuzzing README for recent clang versions
Recent clang versions ship with libfuzzer, so there's no need to build
libfuzzer yourself. They also have a dedicated -fsanitize=fuzzer-no-link
flag and no longer support the sanitize flags described in the fuzzing
README. Update it to reflect all this.
Fixes #8768.
Reviewed-by: Matt Caswell <matt@openssl.org>
Reviewed-by: Kurt Roeckx <kurt@roeckx.be>
GH: #8891
Diffstat (limited to 'fuzz')
-rw-r--r-- | fuzz/README.md | 75 |
1 files changed, 43 insertions, 32 deletions
diff --git a/fuzz/README.md b/fuzz/README.md index 8e7c48d45e..dadf874691 100644 --- a/fuzz/README.md +++ b/fuzz/README.md @@ -3,57 +3,68 @@ 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. - -Update your path: - - $ PATH=~/third_party/llvm-build/Release+Asserts/bin/:$PATH - -Get and build libFuzzer (there is a git mirror at -https://github.com/llvm-mirror/llvm/tree/master/lib/Fuzzer if you prefer): - - $ cd - $ sudo apt-get install subversion - $ mkdir svn-work - $ cd svn-work - $ svn co https://llvm.org/svn/llvm-project/compiler-rt/trunk/lib/fuzzer Fuzzer - $ cd Fuzzer - $ clang++ -c -g -O2 -std=c++11 *.cpp - $ ar r libFuzzer.a *.o - $ ranlib libFuzzer.a - -Configure for fuzzing: +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-6.0/lib/clang/6.0.0/lib/linux/libclang_rt.fuzzer-x86_64.a`. $ CC=clang ./config enable-fuzz-libfuzzer \ - --with-fuzzer-include=../../svn-work/Fuzzer \ - --with-fuzzer-lib=../../svn-work/Fuzzer/libFuzzer.a \ + --with-fuzzer-lib=$PATH_TO_LIBFUZZER \ -DPEDANTIC enable-asan enable-ubsan no-shared \ -DFUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION \ - -fsanitize-coverage=trace-pc-guard,indirect-calls,trace-cmp \ - 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 + +Compile: + $ sudo apt-get install make $ LDCMD=clang++ make -j + +Finally, perform the actual fuzzing: + $ fuzz/helper.py $FUZZER -Where $FUZZER is one of the executables in `fuzz/`. +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/`. +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=$PATH_TO_LIBFUZZER_DIR \ + --with-fuzzer-lib=$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 + AFL === |