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diff --git a/docs/fuzzing_expert.md b/docs/fuzzing_expert.md deleted file mode 100644 index 876c5fbb..00000000 --- a/docs/fuzzing_expert.md +++ /dev/null @@ -1,630 +0,0 @@ -# Fuzzing with AFL++ - -The following describes how to fuzz with a target if source code is available. -If you have a binary-only target please skip to [#Instrumenting binary-only apps](#Instrumenting binary-only apps) - -Fuzzing source code is a three-step process. - -1. Compile the target with a special compiler that prepares the target to be - fuzzed efficiently. This step is called "instrumenting a target". -2. Prepare the fuzzing by selecting and optimizing the input corpus for the - target. -3. Perform the fuzzing of the target by randomly mutating input and assessing - if a generated input was processed in a new path in the target binary. - -### 1. Instrumenting that target - -#### a) Selecting the best AFL++ compiler for instrumenting the target - -AFL++ comes with a central compiler `afl-cc` that incorporates various different -kinds of compiler targets and and instrumentation options. -The following evaluation flow will help you to select the best possible. - -It is highly recommended to have the newest llvm version possible installed, -anything below 9 is not recommended. - -``` -+--------------------------------+ -| clang/clang++ 11+ is available | --> use LTO mode (afl-clang-lto/afl-clang-lto++) -+--------------------------------+ see [instrumentation/README.lto.md](instrumentation/README.lto.md) - | - | if not, or if the target fails with LTO afl-clang-lto/++ - | - v -+---------------------------------+ -| clang/clang++ 3.8+ is available | --> use LLVM mode (afl-clang-fast/afl-clang-fast++) -+---------------------------------+ see [instrumentation/README.llvm.md](instrumentation/README.llvm.md) - | - | if not, or if the target fails with LLVM afl-clang-fast/++ - | - v - +--------------------------------+ - | gcc 5+ is available | -> use GCC_PLUGIN mode (afl-gcc-fast/afl-g++-fast) - +--------------------------------+ see [instrumentation/README.gcc_plugin.md](instrumentation/README.gcc_plugin.md) and - [instrumentation/README.instrument_list.md](instrumentation/README.instrument_list.md) - | - | if not, or if you do not have a gcc with plugin support - | - v - use GCC mode (afl-gcc/afl-g++) (or afl-clang/afl-clang++ for clang) -``` - -Clickable README links for the chosen compiler: - - * [LTO mode - afl-clang-lto](../instrumentation/README.lto.md) - * [LLVM mode - afl-clang-fast](../instrumentation/README.llvm.md) - * [GCC_PLUGIN mode - afl-gcc-fast](../instrumentation/README.gcc_plugin.md) - * GCC/CLANG modes (afl-gcc/afl-clang) have no README as they have no own features - -You can select the mode for the afl-cc compiler by: - 1. use a symlink to afl-cc: afl-gcc, afl-g++, afl-clang, afl-clang++, - afl-clang-fast, afl-clang-fast++, afl-clang-lto, afl-clang-lto++, - afl-gcc-fast, afl-g++-fast (recommended!) - 2. using the environment variable AFL_CC_COMPILER with MODE - 3. passing --afl-MODE command line options to the compiler via CFLAGS/CXXFLAGS/CPPFLAGS - -MODE can be one of: LTO (afl-clang-lto*), LLVM (afl-clang-fast*), GCC_PLUGIN -(afl-g*-fast) or GCC (afl-gcc/afl-g++) or CLANG(afl-clang/afl-clang++). - -Because no AFL specific command-line options are accepted (beside the ---afl-MODE command), the compile-time tools make fairly broad use of environment -variables, which can be listed with `afl-cc -hh` or by reading [env_variables.md](env_variables.md). - -#### b) Selecting instrumentation options - -The following options are available when you instrument with LTO mode (afl-clang-fast/afl-clang-lto): - - * Splitting integer, string, float and switch comparisons so AFL++ can easier - solve these. This is an important option if you do not have a very good - and large input corpus. This technique is called laf-intel or COMPCOV. - To use this set the following environment variable before compiling the - target: `export AFL_LLVM_LAF_ALL=1` - You can read more about this in [instrumentation/README.laf-intel.md](../instrumentation/README.laf-intel.md) - * A different technique (and usually a better one than laf-intel) is to - instrument the target so that any compare values in the target are sent to - AFL++ which then tries to put these values into the fuzzing data at different - locations. This technique is very fast and good - if the target does not - transform input data before comparison. Therefore this technique is called - `input to state` or `redqueen`. - If you want to use this technique, then you have to compile the target - twice, once specifically with/for this mode by setting `AFL_LLVM_CMPLOG=1`, - and pass this binary to afl-fuzz via the `-c` parameter. - Note that you can compile also just a cmplog binary and use that for both - however there will be a performance penality. - You can read more about this in [instrumentation/README.cmplog.md](../instrumentation/README.cmplog.md) - -If you use LTO, LLVM or GCC_PLUGIN mode (afl-clang-fast/afl-clang-lto/afl-gcc-fast) -you have the option to selectively only instrument parts of the target that you -are interested in: - - * To instrument only those parts of the target that you are interested in - create a file with all the filenames of the source code that should be - instrumented. - For afl-clang-lto and afl-gcc-fast - or afl-clang-fast if a mode other than - DEFAULT/PCGUARD is used or you have llvm > 10.0.0 - just put one - filename or function per line (no directory information necessary for - filenames9, and either set `export AFL_LLVM_ALLOWLIST=allowlist.txt` **or** - `export AFL_LLVM_DENYLIST=denylist.txt` - depending on if you want per - default to instrument unless noted (DENYLIST) or not perform instrumentation - unless requested (ALLOWLIST). - **NOTE:** During optimization functions might be inlined and then would not match! - See [instrumentation/README.instrument_list.md](../instrumentation/README.instrument_list.md) - -There are many more options and modes available however these are most of the -time less effective. See: - * [instrumentation/README.ctx.md](../instrumentation/README.ctx.md) - * [instrumentation/README.ngram.md](../instrumentation/README.ngram.md) - -AFL++ performs "never zero" counting in its bitmap. You can read more about this -here: - * [instrumentation/README.neverzero.md](../instrumentation/README.neverzero.md) - -#### c) Sanitizers - -It is possible to use sanitizers when instrumenting targets for fuzzing, -which allows you to find bugs that would not necessarily result in a crash. - -Note that sanitizers have a huge impact on CPU (= less executions per second) -and RAM usage. Also you should only run one afl-fuzz instance per sanitizer type. -This is enough because a use-after-free bug will be picked up, e.g. by -ASAN (address sanitizer) anyway when syncing to other fuzzing instances, -so not all fuzzing instances need to be instrumented with ASAN. - -The following sanitizers have built-in support in AFL++: - * ASAN = Address SANitizer, finds memory corruption vulnerabilities like - use-after-free, NULL pointer dereference, buffer overruns, etc. - Enabled with `export AFL_USE_ASAN=1` before compiling. - * MSAN = Memory SANitizer, finds read access to uninitialized memory, eg. - a local variable that is defined and read before it is even set. - Enabled with `export AFL_USE_MSAN=1` before compiling. - * UBSAN = Undefined Behaviour SANitizer, finds instances where - by the - C and C++ standards - undefined behaviour happens, e.g. adding two - signed integers together where the result is larger than a signed integer - can hold. - Enabled with `export AFL_USE_UBSAN=1` before compiling. - * CFISAN = Control Flow Integrity SANitizer, finds instances where the - control flow is found to be illegal. Originally this was rather to - prevent return oriented programming exploit chains from functioning, - in fuzzing this is mostly reduced to detecting type confusion - vulnerabilities - which is however one of the most important and dangerous - C++ memory corruption classes! - Enabled with `export AFL_USE_CFISAN=1` before compiling. - * TSAN = Thread SANitizer, finds thread race conditions. - Enabled with `export AFL_USE_TSAN=1` before compiling. - * LSAN = Leak SANitizer, finds memory leaks in a program. This is not really - a security issue, but for developers this can be very valuable. - Note that unlike the other sanitizers above this needs - `__AFL_LEAK_CHECK();` added to all areas of the target source code where you - find a leak check necessary! - Enabled with `export AFL_USE_LSAN=1` before compiling. - -It is possible to further modify the behaviour of the sanitizers at run-time -by setting `ASAN_OPTIONS=...`, `LSAN_OPTIONS` etc. - the available parameters -can be looked up in the sanitizer documentation of llvm/clang. -afl-fuzz however requires some specific parameters important for fuzzing to be -set. If you want to set your own, it might bail and report what it is missing. - -Note that some sanitizers cannot be used together, e.g. ASAN and MSAN, and -others often cannot work together because of target weirdness, e.g. ASAN and -CFISAN. You might need to experiment which sanitizers you can combine in a -target (which means more instances can be run without a sanitized target, -which is more effective). - -#### d) Modify the target - -If the target has features that make fuzzing more difficult, e.g. -checksums, HMAC, etc. then modify the source code so that checks for these -values are removed. -This can even be done safely for source code used in operational products -by eliminating these checks within these AFL specific blocks: - -``` -#ifdef FUZZING_BUILD_MODE_UNSAFE_FOR_PRODUCTION - // say that the checksum or HMAC was fine - or whatever is required - // to eliminate the need for the fuzzer to guess the right checksum - return 0; -#endif -``` - -All AFL++ compilers will set this preprocessor definition automatically. - -#### e) Instrument the target - -In this step the target source code is compiled so that it can be fuzzed. - -Basically you have to tell the target build system that the selected AFL++ -compiler is used. Also - if possible - you should always configure the -build system such that the target is compiled statically and not dynamically. -How to do this is described below. - -The #1 rule when instrumenting a target is: avoid instrumenting shared -libraries at all cost. You would need to set LD_LIBRARY_PATH to point to -these, you could accidently type "make install" and install them system wide - -so don't. Really don't. -**Always compile libraries you want to have instrumented as static and link -these to the target program!** - -Then build the target. (Usually with `make`) - -**NOTES** - -1. sometimes configure and build systems are fickle and do not like - stderr output (and think this means a test failure) - which is something - AFL++ likes to do to show statistics. It is recommended to disable AFL++ - instrumentation reporting via `export AFL_QUIET=1`. - -2. sometimes configure and build systems error on warnings - these should be - disabled (e.g. `--disable-werror` for some configure scripts). - -3. in case the configure/build system complains about AFL++'s compiler and - aborts then set `export AFL_NOOPT=1` which will then just behave like the - real compiler. This option has to be unset again before building the target! - -##### configure - -For `configure` build systems this is usually done by: -`CC=afl-clang-fast CXX=afl-clang-fast++ ./configure --disable-shared` - -Note that if you are using the (better) afl-clang-lto compiler you also have to -set AR to llvm-ar[-VERSION] and RANLIB to llvm-ranlib[-VERSION] - as is -described in [instrumentation/README.lto.md](../instrumentation/README.lto.md). - -##### cmake - -For `cmake` build systems this is usually done by: -`mkdir build; cd build; cmake -DCMAKE_C_COMPILER=afl-cc -DCMAKE_CXX_COMPILER=afl-c++ ..` - -Note that if you are using the (better) afl-clang-lto compiler you also have to -set AR to llvm-ar[-VERSION] and RANLIB to llvm-ranlib[-VERSION] - as is -described in [instrumentation/README.lto.md](../instrumentation/README.lto.md). - -##### meson - -For meson you have to set the AFL++ compiler with the very first command! -`CC=afl-cc CXX=afl-c++ meson` - -##### other build systems or if configure/cmake didn't work - -Sometimes cmake and configure do not pick up the AFL++ compiler, or the -ranlib/ar that is needed - because this was just not foreseen by the developer -of the target. Or they have non-standard options. Figure out if there is a -non-standard way to set this, otherwise set up the build normally and edit the -generated build environment afterwards manually to point it to the right compiler -(and/or ranlib and ar). - -#### f) Better instrumentation - -If you just fuzz a target program as-is you are wasting a great opportunity for -much more fuzzing speed. - -This variant requires the usage of afl-clang-lto, afl-clang-fast or afl-gcc-fast. - -It is the so-called `persistent mode`, which is much, much faster but -requires that you code a source file that is specifically calling the target -functions that you want to fuzz, plus a few specific AFL++ functions around -it. See [instrumentation/README.persistent_mode.md](../instrumentation/README.persistent_mode.md) for details. - -Basically if you do not fuzz a target in persistent mode then you are just -doing it for a hobby and not professionally :-). - -#### g) libfuzzer fuzzer harnesses with LLVMFuzzerTestOneInput() - -libfuzzer `LLVMFuzzerTestOneInput()` harnesses are the defacto standard -for fuzzing, and they can be used with AFL++ (and honggfuzz) as well! -Compiling them is as simple as: -``` -afl-clang-fast++ -fsanitize=fuzzer -o harness harness.cpp targetlib.a -``` -You can even use advanced libfuzzer features like `FuzzedDataProvider`, -`LLVMFuzzerMutate()` etc. and they will work! - -The generated binary is fuzzed with afl-fuzz like any other fuzz target. - -Bonus: the target is already optimized for fuzzing due to persistent mode and -shared-memory testcases and hence gives you the fastest speed possible. - -For more information see [utils/aflpp_driver/README.md](../utils/aflpp_driver/README.md) - -### 2. Preparing the fuzzing campaign - -As you fuzz the target with mutated input, having as diverse inputs for the -target as possible improves the efficiency a lot. - -#### a) Collect inputs - -Try to gather valid inputs for the target from wherever you can. E.g. if it is -the PNG picture format try to find as many png files as possible, e.g. from -reported bugs, test suites, random downloads from the internet, unit test -case data - from all kind of PNG software. - -If the input format is not known, you can also modify a target program to write -normal data it receives and processes to a file and use these. - -#### b) Making the input corpus unique - -Use the AFL++ tool `afl-cmin` to remove inputs from the corpus that do not -produce a new path in the target. - -Put all files from step a) into one directory, e.g. INPUTS. - -If the target program is to be called by fuzzing as `bin/target -d INPUTFILE` -the run afl-cmin like this: -`afl-cmin -i INPUTS -o INPUTS_UNIQUE -- bin/target -d @@` -Note that the INPUTFILE argument that the target program would read from has to be set as `@@`. - -If the target reads from stdin instead, just omit the `@@` as this is the -default. - -This step is highly recommended! - -#### c) Minimizing all corpus files - -The shorter the input files that still traverse the same path -within the target, the better the fuzzing will be. This minimization -is done with `afl-tmin` however it is a long process as this has to -be done for every file: - -``` -mkdir input -cd INPUTS_UNIQUE -for i in *; do - afl-tmin -i "$i" -o "../input/$i" -- bin/target -d @@ -done -``` - -This step can also be parallelized, e.g. with `parallel`. -Note that this step is rather optional though. - -#### Done! - -The INPUTS_UNIQUE/ directory from step b) - or even better the directory input/ -if you minimized the corpus in step c) - is the resulting input corpus directory -to be used in fuzzing! :-) - -### 3. Fuzzing the target - -In this final step we fuzz the target. -There are not that many important options to run the target - unless you want -to use many CPU cores/threads for the fuzzing, which will make the fuzzing much -more useful. - -If you just use one CPU for fuzzing, then you are fuzzing just for fun and not -seriously :-) - -#### a) Running afl-fuzz - -Before you do even a test run of afl-fuzz execute `sudo afl-system-config` (on -the host if you execute afl-fuzz in a docker container). This reconfigures the -system for optimal speed - which afl-fuzz checks and bails otherwise. -Set `export AFL_SKIP_CPUFREQ=1` for afl-fuzz to skip this check if you cannot -run afl-system-config with root privileges on the host for whatever reason. - -Note there is also `sudo afl-persistent-config` which sets additional permanent -boot options for a much better fuzzing performance. - -Note that both scripts improve your fuzzing performance but also decrease your -system protection against attacks! So set strong firewall rules and only -expose SSH as a network service if you use these (which is highly recommended). - -If you have an input corpus from step 2 then specify this directory with the `-i` -option. Otherwise create a new directory and create a file with any content -as test data in there. - -If you do not want anything special, the defaults are already usually best, -hence all you need is to specify the seed input directory with the result of -step [2a. Collect inputs](#a-collect-inputs): -`afl-fuzz -i input -o output -- bin/target -d @@` -Note that the directory specified with -o will be created if it does not exist. - -It can be valuable to run afl-fuzz in a screen or tmux shell so you can log off, -or afl-fuzz is not aborted if you are running it in a remote ssh session where -the connection fails in between. -Only do that though once you have verified that your fuzzing setup works! -Simply run it like `screen -dmS afl-main -- afl-fuzz -M main-$HOSTNAME -i ...` -and it will start away in a screen session. To enter this session simply type -`screen -r afl-main`. You see - it makes sense to name the screen session -same as the afl-fuzz -M/-S naming :-) -For more information on screen or tmux please check their documentation. - -If you need to stop and re-start the fuzzing, use the same command line options -(or even change them by selecting a different power schedule or another -mutation mode!) and switch the input directory with a dash (`-`): -`afl-fuzz -i - -o output -- bin/target -d @@` - -Memory limits are not enforced by afl-fuzz by default and the system may run -out of memory. You can decrease the memory with the `-m` option, the value is -in MB. If this is too small for the target, you can usually see this by -afl-fuzz bailing with the message that it could not connect to the forkserver. - -Adding a dictionary is helpful. See the directory [dictionaries/](../dictionaries/) if -something is already included for your data format, and tell afl-fuzz to load -that dictionary by adding `-x dictionaries/FORMAT.dict`. With afl-clang-lto -you have an autodictionary generation for which you need to do nothing except -to use afl-clang-lto as the compiler. You also have the option to generate -a dictionary yourself, see [utils/libtokencap/README.md](../utils/libtokencap/README.md). - -afl-fuzz has a variety of options that help to workaround target quirks like -specific locations for the input file (`-f`), performing deterministic -fuzzing (`-D`) and many more. Check out `afl-fuzz -h`. - -We highly recommend that you set a memory limit for running the target with `-m` -which defines the maximum memory in MB. This prevents a potential -out-of-memory problem for your system plus helps you detect missing `malloc()` -failure handling in the target. -Play around with various -m values until you find one that safely works for all -your input seeds (if you have good ones and then double or quadrouple that. - -By default afl-fuzz never stops fuzzing. To terminate AFL++ simply press Control-C -or send a signal SIGINT. You can limit the number of executions or approximate runtime -in seconds with options also. - -When you start afl-fuzz you will see a user interface that shows what the status -is: - - -All labels are explained in [status_screen.md](status_screen.md). - -#### b) Using multiple cores - -If you want to seriously fuzz then use as many cores/threads as possible to -fuzz your target. - -On the same machine - due to the design of how AFL++ works - there is a maximum -number of CPU cores/threads that are useful, use more and the overall performance -degrades instead. This value depends on the target, and the limit is between 32 -and 64 cores per machine. - -If you have the RAM, it is highly recommended run the instances with a caching -of the testcases. Depending on the average testcase size (and those found -during fuzzing) and their number, a value between 50-500MB is recommended. -You can set the cache size (in MB) by setting the environment variable `AFL_TESTCACHE_SIZE`. - -There should be one main fuzzer (`-M main-$HOSTNAME` option) and as many secondary -fuzzers (eg `-S variant1`) as you have cores that you use. -Every -M/-S entry needs a unique name (that can be whatever), however the same --o output directory location has to be used for all instances. - -For every secondary fuzzer there should be a variation, e.g.: - * one should fuzz the target that was compiled differently: with sanitizers - activated (`export AFL_USE_ASAN=1 ; export AFL_USE_UBSAN=1 ; - export AFL_USE_CFISAN=1`) - * one or two should fuzz the target with CMPLOG/redqueen (see above), at - least one cmplog instance should follow transformations (`-l AT`) - * one to three fuzzers should fuzz a target compiled with laf-intel/COMPCOV - (see above). Important note: If you run more than one laf-intel/COMPCOV - fuzzer and you want them to share their intermediate results, the main - fuzzer (`-M`) must be one of the them! (Although this is not really - recommended.) - -All other secondaries should be used like this: - * A quarter to a third with the MOpt mutator enabled: `-L 0` - * run with a different power schedule, recommended are: - `fast (default), explore, coe, lin, quad, exploit and rare` - which you can set with e.g. `-p explore` - * a few instances should use the old queue cycling with `-Z` - -Also it is recommended to set `export AFL_IMPORT_FIRST=1` to load testcases -from other fuzzers in the campaign first. - -If you have a large corpus, a corpus from a previous run or are fuzzing in -a CI, then also set `export AFL_CMPLOG_ONLY_NEW=1` and `export AFL_FAST_CAL=1`. - -You can also use different fuzzers. -If you are using AFL spinoffs or AFL conforming fuzzers, then just use the -same -o directory and give it a unique `-S` name. -Examples are: - * [Fuzzolic](https://github.com/season-lab/fuzzolic) - * [symcc](https://github.com/eurecom-s3/symcc/) - * [Eclipser](https://github.com/SoftSec-KAIST/Eclipser/) - * [AFLsmart](https://github.com/aflsmart/aflsmart) - * [FairFuzz](https://github.com/carolemieux/afl-rb) - * [Neuzz](https://github.com/Dongdongshe/neuzz) - * [Angora](https://github.com/AngoraFuzzer/Angora) - -A long list can be found at [https://github.com/Microsvuln/Awesome-AFL](https://github.com/Microsvuln/Awesome-AFL) - -However you can also sync AFL++ with honggfuzz, libfuzzer with `-entropic=1`, etc. -Just show the main fuzzer (-M) with the `-F` option where the queue/work -directory of a different fuzzer is, e.g. `-F /src/target/honggfuzz`. -Using honggfuzz (with `-n 1` or `-n 2`) and libfuzzer in parallel is highly -recommended! - -#### c) Using multiple machines for fuzzing - -Maybe you have more than one machine you want to fuzz the same target on. -Simply start the `afl-fuzz` (and perhaps libfuzzer, honggfuzz, ...) -orchestra as you like, just ensure that your have one and only one `-M` -instance per server, and that its name is unique, hence the recommendation -for `-M main-$HOSTNAME`. - -Now there are three strategies on how you can sync between the servers: - * never: sounds weird, but this makes every server an island and has the - chance the each follow different paths into the target. You can make - this even more interesting by even giving different seeds to each server. - * regularly (~4h): this ensures that all fuzzing campaigns on the servers - "see" the same thing. It is like fuzzing on a huge server. - * in intervals of 1/10th of the overall expected runtime of the fuzzing you - sync. This tries a bit to combine both. have some individuality of the - paths each campaign on a server explores, on the other hand if one - gets stuck where another found progress this is handed over making it - unstuck. - -The syncing process itself is very simple. -As the `-M main-$HOSTNAME` instance syncs to all `-S` secondaries as well -as to other fuzzers, you have to copy only this directory to the other -machines. - -Lets say all servers have the `-o out` directory in /target/foo/out, and -you created a file `servers.txt` which contains the hostnames of all -participating servers, plus you have an ssh key deployed to all of them, -then run: -```bash -for FROM in `cat servers.txt`; do - for TO in `cat servers.txt`; do - rsync -rlpogtz --rsh=ssh $FROM:/target/foo/out/main-$FROM $TO:target/foo/out/ - done -done -``` -You can run this manually, per cron job - as you need it. -There is a more complex and configurable script in `utils/distributed_fuzzing`. - -#### d) The status of the fuzz campaign - -AFL++ comes with the `afl-whatsup` script to show the status of the fuzzing -campaign. - -Just supply the directory that afl-fuzz is given with the -o option and -you will see a detailed status of every fuzzer in that campaign plus -a summary. - -To have only the summary use the `-s` switch e.g.: `afl-whatsup -s out/` - -If you have multiple servers then use the command after a sync, or you have -to execute this script per server. - -Another tool to inspect the current state and history of a specific instance -is afl-plot, which generates an index.html file and a graphs that show how -the fuzzing instance is performing. -The syntax is `afl-plot instance_dir web_dir`, e.g. `afl-plot out/default /srv/www/htdocs/plot` - -#### e) Stopping fuzzing, restarting fuzzing, adding new seeds - -To stop an afl-fuzz run, simply press Control-C. - -To restart an afl-fuzz run, just reuse the same command line but replace the -`-i directory` with `-i -` or set `AFL_AUTORESUME=1`. - -If you want to add new seeds to a fuzzing campaign you can run a temporary -fuzzing instance, e.g. when your main fuzzer is using `-o out` and the new -seeds are in `newseeds/` directory: -``` -AFL_BENCH_JUST_ONE=1 AFL_FAST_CAL=1 afl-fuzz -i newseeds -o out -S newseeds -- ./target -``` - -#### f) Checking the coverage of the fuzzing - -The `paths found` value is a bad indicator for checking how good the coverage is. - -A better indicator - if you use default llvm instrumentation with at least -version 9 - is to use `afl-showmap` with the collect coverage option `-C` on -the output directory: -``` -$ afl-showmap -C -i out -o /dev/null -- ./target -params @@ -... -[*] Using SHARED MEMORY FUZZING feature. -[*] Target map size: 9960 -[+] Processed 7849 input files. -[+] Captured 4331 tuples (highest value 255, total values 67130596) in '/dev/nul -l'. -[+] A coverage of 4331 edges were achieved out of 9960 existing (43.48%) with 7849 input files. -``` -It is even better to check out the exact lines of code that have been reached - -and which have not been found so far. - -An "easy" helper script for this is [https://github.com/vanhauser-thc/afl-cov](https://github.com/vanhauser-thc/afl-cov), -just follow the README of that separate project. - -If you see that an important area or a feature has not been covered so far then -try to find an input that is able to reach that and start a new secondary in -that fuzzing campaign with that seed as input, let it run for a few minutes, -then terminate it. The main node will pick it up and make it available to the -other secondary nodes over time. Set `export AFL_NO_AFFINITY=1` or -`export AFL_TRY_AFFINITY=1` if you have no free core. - -Note that in nearly all cases you can never reach full coverage. A lot of -functionality is usually dependent on exclusive options that would need individual -fuzzing campaigns each with one of these options set. E.g. if you fuzz a library to -convert image formats and your target is the png to tiff API then you will not -touch any of the other library APIs and features. - -#### g) How long to fuzz a target? - -This is a difficult question. -Basically if no new path is found for a long time (e.g. for a day or a week) -then you can expect that your fuzzing won't be fruitful anymore. -However often this just means that you should switch out secondaries for -others, e.g. custom mutator modules, sync to very different fuzzers, etc. - -Keep the queue/ directory (for future fuzzings of the same or similar targets) -and use them to seed other good fuzzers like libfuzzer with the -entropic -switch or honggfuzz. - -#### h) Improve the speed! - - * Use [persistent mode](../instrumentation/README.persistent_mode.md) (x2-x20 speed increase) - * If you do not use shmem persistent mode, use `AFL_TMPDIR` to point the input file on a tempfs location, see [env_variables.md](env_variables.md) - * Linux: Improve kernel performance: modify `/etc/default/grub`, set `GRUB_CMDLINE_LINUX_DEFAULT="ibpb=off ibrs=off kpti=off l1tf=off mds=off mitigations=off no_stf_barrier noibpb noibrs nopcid nopti nospec_store_bypass_disable nospectre_v1 nospectre_v2 pcid=off pti=off spec_store_bypass_disable=off spectre_v2=off stf_barrier=off"`; then `update-grub` and `reboot` (warning: makes the system more insecure) - you can also just run `sudo afl-persistent-config` - * Linux: Running on an `ext2` filesystem with `noatime` mount option will be a bit faster than on any other journaling filesystem - * Use your cores! [b) Using multiple cores](#b-using-multiple-cores) - * Run `sudo afl-system-config` before starting the first afl-fuzz instance after a reboot - -### The End - -Check out the [FAQ](FAQ.md) if it maybe answers your question (that -you might not even have known you had ;-) ). - -This is basically all you need to know to professionally run fuzzing campaigns. -If you want to know more, the tons of texts in [docs/](./) will have you covered. - -Note that there are also a lot of tools out there that help fuzzing with AFL++ -(some might be deprecated or unsupported), see [tools.md](tools.md). \ No newline at end of file |