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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
master
Brian Chen 3 years ago
committed by Kurt Roeckx
parent
commit
639b53ecd8
1 changed files with 43 additions and 32 deletions
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      fuzz/README.md

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fuzz/README.md View File

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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
===


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