diff options
Diffstat (limited to 'README.md')
| -rw-r--r-- | README.md | 135 |
1 files changed, 135 insertions, 0 deletions
diff --git a/README.md b/README.md new file mode 100644 index 0000000..801f678 --- /dev/null +++ b/README.md @@ -0,0 +1,135 @@ +# 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. |