From 639b53ecd82648fbb66a2ab7dabece7f15a1f730 Mon Sep 17 00:00:00 2001
From: Brian Chen <brian.chxn@gmail.com>
Date: Tue, 7 May 2019 04:05:44 -0400
Subject: [PATCH] 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
---
fuzz/README.md | 75 +++++++++++++++++++++++++++++---------------------
1 file 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
===
--
2.25.1