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authorvan Hauser <vh@thc.org>2019-01-04 11:24:24 +0100
committervan Hauser <vh@thc.org>2019-01-04 11:24:24 +0100
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-# American Fuzzy Lop + Dyninst == AFL Fuzzing blackbox binaries
-
-The tool has two parts. The instrumentation tool and the instrumentation 
-library. Instrumentation library has an initialization callback and basic 
-block callback functions which are designed to emulate what AFL is doing
-with afl-gcc/afl-g++/afl-as. 
-Instrumentation tool (afl-dyninst) instruments the supplied binary by
-inserting callbacks for each basic block and an initialization 
-callback either at _init or at specified entry point.
-
-
-## Building / Compiling
-
-0. Clone, compile and install dyninst: https://github.com/dyninst/dyninst/
-
-Note that you can also use dyninst 9.3.2, its actually less hassle, but has less platform support. And different bugs :)
-
-1. Edit the Makefile and set DYNINST_ROOT and AFL_ROOT to appropriate paths. 
-
-if you installed dyninst 10.x or from github you also have to set DYNINST_BUILD set DYNINST_OPT to $(DYNINST10)
-
-2. make
-
-3. make install
-
-
-## Commandline options
-
-Usage: ./afl-dyninst-dfvD -i <binary> -o <binary> -l <library> -e <address> -E <address> -s <number> -S <funcname> -m <size>
-   -i: input binary 
-   -o: output binary
-   -d: do not instrument the binary, only supplied libraries
-   -l: linked library to instrument (repeat for more than one)
-   -r: runtime library to instrument (path to, repeat for more than one)
-   -e: entry point address to patch (required for stripped binaries)
-   -E: exit point - force exit(0) at this address (repeat for more than one)
-   -s: number of initial basic blocks to skip in binary
-   -m: minimum size of a basic bock to instrument (default: 1)
-   -f: try to fix a dyninst bug that leads to crashes
-   -S: do not instrument this function (repeat for more than one)
-   -D: instrument fork server and forced exit functions but no basic blocks
-   -x: experimental performance modes (can be set up to three times)
-         level 1: ~40-50%% improvement
-         level 2: ~100%% vs normal, ~40%% vs level 1
-         level 3: ~110%% vs normal, ~5%% vs level 2
-       level 3 replaces how basic block coverage works and can be tried if
-       normal mode or level 1 or 2 lead to crashes randomly.
-   -v: verbose output
-
-Switch -l is used to supply the names of the libraries that should 
-be instrumented along the binary. Instrumented libraries will be copied
-to the current working directory. This option can be repeated as many times
-as needed. Depending on the environment, the LD_LIBRARY_PATH should be set 
-to point to instrumented libraries while fuzzing. 
-
-Switch -e is used to manualy specify the entry point where initialization
-callback is to be inserted. For unstipped binaries, afl-dyninst defaults 
-to using _init of the binary as an entry point. In case of stripped binaries
-this option is required and is best set to the address of main which 
-can easily be determined by disassembling the binary and looking for an 
-argument to __libc_start_main. 
-
-Switch -E is used to specify addresses that should force a clean exit
-when reached. This can speed up the fuzzing tremendously.
-
-Switch -s instructs afl-dyninst to skip the first <number> of basic
-blocks. Currently, it is used to work around a bug in Dyninst
-but doubles as an optimization option, as skipping the basic blocks 
-of the initialization routines makes things run faster. If the instrumented
-binary is crashing by itself, try skiping a number of blocks.
-
-Switch -r allows you to specify a path to the library that is loaded
-via dlopen() at runtime. Instrumented runtime libraries will be 
-written to the same location with a ".ins" suffix as not to overwrite
-the original ones. Make sure to backup the originals and then rename the
-instrumented ones to original name. 
-
-Switch -m allows you to only instrument basic blocks of a minimum size - the
-default minimum size is 1
-
-Switch -f fixes a dyninst bug that lead to bugs in the instrumented program:
-our basic block instrumentation function loaded into the instrumentd binaries
-uses the edi/rdi. However dyninst does not always saves and restores it when
-instrumenting that function leading to crashes and changed program behaviour
-when the register is used for function parameters.
-
-Switch -S allows you to not instrument specific functions.
-This options is mainly to hunt down bugs in dyninst.
-
-Switch -D installs the afl fork server and forced exit functions but no
-basic block instrumentation. That would serve no purpose - unless there is
-another interesting tool coming up: afl-pin (already available at
-https://github.com/vanhauser-thc/afl-pin) and afl-dynamorio (wip)
-
-Switch -x enables performance modes, -x level 1, -xx level 2 and  -xxx level 3
-level 3 is only availble for intel x64 and can either save your ass or not
-work for you whatsoever.
-level 1 (-x) is highly recommended (+50%).
-level 2 (-xx) gives an additonal 40% but removes (usually unnecessary) precautions
-level 3 (-xxx) gives only a very small additional speed and works differently,
- it basically replaces the instrumented instructions by dyninst with own ones.
- this is a good idea when you run into dyninst bugs.
-
-
-## Example of running the tool
-
-Dyninst requires DYNINSTAPI_RT_LIB environment variable to point to the location
-of libdyninstAPI_RT.so.
-
-$ export DYNINSTAPI_RT_LIB=/usr/local/lib/libdyninstAPI_RT.so
-$ ./afl-dyninst -i ./rar -o ./rar_ins -e 0x4034c0 -s 100
-Skipping library: libAflDyninst.so
-Instrumenting module: DEFAULT_MODULE
-Inserting init callback.
-Saving the instrumented binary to ./rar_ins...
-All done! Happy fuzzing!
-
-Here we are instrumenting the rar binary with entrypoint at 0x4034c0
-(manualy found address of main), skipping the first 100 basic blocks 
-and outputing to rar_ins. 
-
-
-## Running AFL on instrumented binary
-
-NOTE: The instrumentation library "libDyninst.so" must be available in the current working
-directory or LD_LIBRARY_PATH as that is where the instrumented binary will be looking for it.
-
-Since AFL checks if the binary has been instrumented by afl-gcc,AFL_SKIP_BIN_CHECK environment 
-variable needs to be set. No modifications to AFL it self is needed. 
-$ export AFL_SKIP_BIN_CHECK=1
-Then, AFL can be run as usual:
-$ afl-fuzz -i testcases/archives/common/gzip/ -o test_gzip -- ./gzip_ins -d -c 
-
-Note that there are the helper scripts afl-fuzz-dyninst.sh and afl-dyninst.sh for you which set the
-required environment variables for you.