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Diffstat (limited to 'docs')
| -rw-r--r-- | docs/Changelog.md | 6 | ||||
| -rw-r--r-- | docs/binaryonly_fuzzing.md | 10 | ||||
| -rw-r--r-- | docs/env_variables.md | 907 | ||||
| -rw-r--r-- | docs/features.md | 31 | ||||
| -rw-r--r-- | docs/technical_details.md | 2 |
5 files changed, 493 insertions, 463 deletions
diff --git a/docs/Changelog.md b/docs/Changelog.md index 6a9c895c..054f0fef 100644 --- a/docs/Changelog.md +++ b/docs/Changelog.md @@ -10,12 +10,14 @@ sending a mail to <afl-users+subscribe@googlegroups.com>. ### Version ++3.15a (dev) - documentation restructuring, made possible by Google Season of Docs :) + - new binary-only fuzzing mode: coresight_mode for aarch64 CPUs :) + thanks to RICSecLab submitting! - afl-fuzz: - cmplog binaries will need to be recompiled for this version (it is better!) - fix a regression introduced in 3.10 that resulted in less coverage being detected. thanks to Collin May for reporting! - - added AFL_IGNORE_PROBLEMS plus checks to identify and abort on + - added AFL_IGNORE_PROBLEMS, plus checks to identify and abort on incorrect LTO usage setups and enhanced the READMEs for better information on how to deal with instrumenting libraries - fix -n dumb mode (nobody should use this) @@ -30,6 +32,8 @@ sending a mail to <afl-users+subscribe@googlegroups.com>. - honor persistent mode for more speed. thanks to dloffre-snl for reporting! - fix bug where targets are not killed on timeouts + - moved hidden afl-showmap -A option to -H to be used for + coresight_mode - Prevent accidently killing non-afl/fuzz services when aborting afl-showmap and other tools. - afl-cc: diff --git a/docs/binaryonly_fuzzing.md b/docs/binaryonly_fuzzing.md index de360543..2c0872cf 100644 --- a/docs/binaryonly_fuzzing.md +++ b/docs/binaryonly_fuzzing.md @@ -175,13 +175,9 @@ ## CORESIGHT Coresight is ARM's answer to Intel's PT. - There is no implementation so far which handles coresight and getting - it working on an ARM Linux is very difficult due to custom kernel building - on embedded systems is difficult. And finding one that has coresight in - the ARM chip is difficult too. - My guess is that it is slower than Qemu, but faster than Intel PT. - - If anyone finds any coresight implementation for AFL please ping me: vh@thc.org + With afl++ v3.15 there is a coresight tracer implementation available in + `coresight_mode/` which is faster than QEMU, however can not run in parallel. + Currently only one process can be traced, it is WIP. ## PIN & DYNAMORIO diff --git a/docs/env_variables.md b/docs/env_variables.md index 5f5c2510..65cca0dc 100644 --- a/docs/env_variables.md +++ b/docs/env_variables.md @@ -1,88 +1,78 @@ -# Environmental variables +# Environment variables - This document discusses the environment variables used by American Fuzzy Lop++ - to expose various exotic functions that may be (rarely) useful for power - users or for some types of custom fuzzing setups. See [../README.md](../README.md) for the general - instruction manual. + This document discusses the environment variables used by AFL++ to expose + various exotic functions that may be (rarely) useful for power users or for + some types of custom fuzzing setups. For general information about AFL++, see + [README.md](../README.md). - Note that most tools will warn on any unknown AFL environment variables. - This is for warning on typos that can happen. If you want to disable this - check then set the `AFL_IGNORE_UNKNOWN_ENVS` environment variable. + Note: Most tools will warn on any unknown AFL++ environment variables; for + example, because of typos. If you want to disable this check, then set the + `AFL_IGNORE_UNKNOWN_ENVS` environment variable. ## 1) Settings for all compilers -Starting with AFL++ 3.0 there is only one compiler: afl-cc -To select the different instrumentation modes this can be done by - 1. passing the --afl-MODE command line option to the compiler - 2. or using 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 - 3. or using the environment variable `AFL_CC_COMPILER` with `MODE` - -`MODE` can be one of `LTO` (afl-clang-lto*), `LLVM` (afl-clang-fast*), `GCC_PLUGIN` -(afl-g*-fast) or `GCC` (afl-gcc/afl-g++). - -Because (with the exception of the --afl-MODE command line option) the -compile-time tools do not accept AFL specific command-line options, they -make fairly broad use of environmental variables instead: - - - Some build/configure scripts break with AFL++ compilers. To be able to - pass them, do: -``` - export CC=afl-cc - export CXX=afl-c++ - export AFL_NOOPT=1 - ./configure --disable-shared --disabler-werror - unset AFL_NOOPT - make -``` - - - Most AFL tools do not print any output if stdout/stderr are redirected. - If you want to get the output into a file then set the `AFL_DEBUG` - environment variable. - This is sadly necessary for various build processes which fail otherwise. +Starting with AFL++ 3.0, there is only one compiler: afl-cc. + +To select the different instrumentation modes, use one of the following options: + + - Pass the --afl-MODE command-line option to the compiler. Only this option + accepts further AFL-specific command-line options. + - Use a symlink to afl-cc: afl-clang, afl-clang++, afl-clang-fast, + afl-clang-fast++, afl-clang-lto, afl-clang-lto++, afl-g++, afl-g++-fast, + afl-gcc, afl-gcc-fast. This option does not accept AFL-specific command-line + options. Instead, use environment variables. + - Use the `AFL_CC_COMPILER` environment variable with `MODE`. To select + `MODE`, use one of the following values: + + - `GCC` (afl-gcc/afl-g++) + - `GCC_PLUGIN` (afl-g*-fast) + - `LLVM` (afl-clang-fast*) + - `LTO` (afl-clang-lto*). + +The compile-time tools do not accept AFL-specific command-line options. The +--afl-MODE command line option is the only exception. The other options make +fairly broad use of environment variables instead: + + - Some build/configure scripts break with AFL++ compilers. To be able to pass + them, do: + + ``` + export CC=afl-cc + export CXX=afl-c++ + export AFL_NOOPT=1 + ./configure --disable-shared --disabler-werror + unset AFL_NOOPT + make + ``` + + - Setting `AFL_AS`, `AFL_CC`, and `AFL_CXX` lets you use alternate downstream + compilation tools, rather than the default 'as', 'clang', or 'gcc' binaries + in your `$PATH`. - - Setting `AFL_HARDEN` automatically adds code hardening options when invoking - the downstream compiler. This currently includes `-D_FORTIFY_SOURCE=2` and - `-fstack-protector-all`. The setting is useful for catching non-crashing - memory bugs at the expense of a very slight (sub-5%) performance loss. + - If you are a weird person that wants to compile and instrument asm text + files, then use the `AFL_AS_FORCE_INSTRUMENT` variable: + `AFL_AS_FORCE_INSTRUMENT=1 afl-gcc foo.s -o foo` + + - Most AFL tools do not print any output if stdout/stderr are redirected. If + you want to get the output into a file, then set the `AFL_DEBUG` environment + variable. This is sadly necessary for various build processes which fail + otherwise. - By default, the wrapper appends `-O3` to optimize builds. Very rarely, this will cause problems in programs built with -Werror, simply because `-O3` - enables more thorough code analysis and can spew out additional warnings. - To disable optimizations, set `AFL_DONT_OPTIMIZE`. - However if `-O...` and/or `-fno-unroll-loops` are set, these are not - overridden. - - - Setting `AFL_USE_ASAN` automatically enables ASAN, provided that your - compiler supports it. - - (You can also enable MSAN via `AFL_USE_MSAN`; ASAN and MSAN come with the - same gotchas; the modes are mutually exclusive. UBSAN can be enabled - similarly by setting the environment variable `AFL_USE_UBSAN=1`. Finally - there is the Control Flow Integrity sanitizer that can be activated by - `AFL_USE_CFISAN=1`) - - - Setting `AFL_USE_LSAN` automatically enables Leak-Sanitizer, provided - that your compiler supports it. To perform a leak check within your - program at a certain point (such as at the end of an __AFL_LOOP), - you can run the macro __AFL_LEAK_CHECK(); which will cause - an abort if any memory is leaked (you can combine this with the - LSAN_OPTIONS=suppressions option to supress some known leaks). - - - Setting `AFL_CC`, `AFL_CXX`, and `AFL_AS` lets you use alternate downstream - compilation tools, rather than the default 'clang', 'gcc', or 'as' binaries - in your `$PATH`. + enables more thorough code analysis and can spew out additional warnings. To + disable optimizations, set `AFL_DONT_OPTIMIZE`. However, if `-O...` and/or + `-fno-unroll-loops` are set, these are not overridden. - - `AFL_PATH` can be used to point afl-gcc to an alternate location of afl-as. - One possible use of this is utils/clang_asm_normalize/, which lets - you instrument hand-written assembly when compiling clang code by plugging - a normalizer into the chain. (There is no equivalent feature for GCC.) + - Setting `AFL_HARDEN` automatically adds code hardening options when invoking + the downstream compiler. This currently includes `-D_FORTIFY_SOURCE=2` and + `-fstack-protector-all`. The setting is useful for catching non-crashing + memory bugs at the expense of a very slight (sub-5%) performance loss. - Setting `AFL_INST_RATIO` to a percentage between 0 and 100 controls the - probability of instrumenting every branch. This is (very rarely) useful - when dealing with exceptionally complex programs that saturate the output - bitmap. Examples include v8, ffmpeg, and perl. + probability of instrumenting every branch. This is (very rarely) useful when + dealing with exceptionally complex programs that saturate the output bitmap. + Examples include ffmpeg, perl, and v8. (If this ever happens, afl-fuzz will warn you ahead of the time by displaying the "bitmap density" field in fiery red.) @@ -90,491 +80,524 @@ make fairly broad use of environmental variables instead: Setting `AFL_INST_RATIO` to 0 is a valid choice. This will instrument only the transitions between function entry points, but not individual branches. - Note that this is an outdated variable. A few instances (e.g. afl-gcc) - still support these, but state-of-the-art (e.g. LLVM LTO and LLVM PCGUARD) - do not need this. + Note that this is an outdated variable. A few instances (e.g. afl-gcc) still + support these, but state-of-the-art (e.g. LLVM LTO and LLVM PCGUARD) do not + need this. - `AFL_NO_BUILTIN` causes the compiler to generate code suitable for use with libtokencap.so (but perhaps running a bit slower than without the flag). + - `AFL_PATH` can be used to point afl-gcc to an alternate location of afl-as. + One possible use of this is utils/clang_asm_normalize/, which lets you + instrument hand-written assembly when compiling clang code by plugging a + normalizer into the chain. (There is no equivalent feature for GCC.) + + - Setting `AFL_QUIET` will prevent afl-as and afl-cc banners from being + displayed during compilation, in case you find them distracting. + + - Setting `AFL_USE_...` automatically enables supported sanitizers - provided + that your compiler supports it. Available are: + - `AFL_USE_ASAN=1` - activates the address sanitizer (memory corruption + detection) + - `AFL_USE_CFISAN=1` - activates the Control Flow Integrity sanitizer (e.g. + type confusion vulnerabilities) + - `AFL_USE_LSAN` - activates the leak sanitizer. To perform a leak check + within your program at a certain point (such as at the end of an + `__AFL_LOOP()`), you can run the macro `__AFL_LEAK_CHECK();` which will + cause an abort if any memory is leaked (you can combine this with the + `LSAN_OPTIONS=...` suppression option to suppress some known leaks). + - `AFL_USE_MSAN=1` - activates the memory sanitizer (uninitialized memory) + - `AFL_USE_TSAN=1` - activates the thread sanitizer to find thread race + conditions + - `AFL_USE_UBSAN=1` - activates the undefined behaviour sanitizer + - `TMPDIR` is used by afl-as for temporary files; if this variable is not set, the tool defaults to /tmp. - - If you are a weird person that wants to compile and instrument asm - text files then use the `AFL_AS_FORCE_INSTRUMENT` variable: - `AFL_AS_FORCE_INSTRUMENT=1 afl-gcc foo.s -o foo` +## 2) Settings for LLVM and LTO: afl-clang-fast / afl-clang-fast++ / afl-clang-lto / afl-clang-lto++ - - Setting `AFL_QUIET` will prevent afl-cc and afl-as banners from being - displayed during compilation, in case you find them distracting. +The native instrumentation helpers (instrumentation and gcc_plugin) accept a +subset of the settings discussed in section 1, with the exception of: -## 2) Settings for LLVM and LTO: afl-clang-fast / afl-clang-fast++ / afl-clang-lto / afl-clang-lto++ + - `AFL_AS`, since this toolchain does not directly invoke GNU `as`. -The native instrumentation helpers (instrumentation and gcc_plugin) accept a subset -of the settings discussed in section 1, with the exception of: + - `AFL_INST_RATIO`, as we use collision free instrumentation by default. Not + all passes support this option though as it is an outdated feature. - LLVM modes support `AFL_LLVM_DICT2FILE=/absolute/path/file.txt` which will - write all constant string comparisons to this file to be used later with + write all constant string comparisons to this file to be used later with afl-fuzz' `-x` option. - - `AFL_AS`, since this toolchain does not directly invoke GNU as. - - `TMPDIR` and `AFL_KEEP_ASSEMBLY`, since no temporary assembly files are created. - - `AFL_INST_RATIO`, as we by default use collision free instrumentation. - Not all passes support this option though as it is an outdated feature. - -Then there are a few specific features that are only available in instrumentation mode: +Then there are a few specific features that are only available in +instrumentation mode: ### Select the instrumentation mode - - `AFL_LLVM_INSTRUMENT` - this configures the instrumentation mode. - Available options: - PCGUARD - our own pcgard based instrumentation (default) - NATIVE - clang's original pcguard based instrumentation - CLASSIC - classic AFL (map[cur_loc ^ prev_loc >> 1]++) (default) - LTO - LTO instrumentation (see below) - CTX - context sensitive instrumentation (see below) - NGRAM-x - deeper previous location coverage (from NGRAM-2 up to NGRAM-16) - GCC - outdated gcc instrumentation - CLANG - outdated clang instrumentation - In CLASSIC you can also specify CTX and/or NGRAM, seperate the options - with a comma "," then, e.g.: - `AFL_LLVM_INSTRUMENT=CLASSIC,CTX,NGRAM-4` - Note that this is actually not a good idea to use both CTX and NGRAM :) +`AFL_LLVM_INSTRUMENT` - this configures the instrumentation mode. + +Available options: -### LTO + - CLANG - outdated clang instrumentation + - CLASSIC - classic AFL (map[cur_loc ^ prev_loc >> 1]++) (default) - This is a different kind way of instrumentation: first it compiles all - code in LTO (link time optimization) and then performs an edge inserting - instrumentation which is 100% collision free (collisions are a big issue - in AFL and AFL-like instrumentations). This is performed by using - afl-clang-lto/afl-clang-lto++ instead of afl-clang-fast, but is only - built if LLVM 11 or newer is used. + You can also specify CTX and/or NGRAM, seperate the options with a comma "," + then, e.g.: `AFL_LLVM_INSTRUMENT=CLASSIC,CTX,NGRAM-4` - - `AFL_LLVM_INSTRUMENT=CFG` will use Control Flow Graph instrumentation. - (not recommended for afl-clang-fast, default for afl-clang-lto as there - it is a different and better kind of instrumentation.) + Note: It is actually not a good idea to use both CTX and NGRAM. :) + - CTX - context sensitive instrumentation + - GCC - outdated gcc instrumentation + - LTO - LTO instrumentation + - NATIVE - clang's original pcguard based instrumentation + - NGRAM-x - deeper previous location coverage (from NGRAM-2 up to NGRAM-16) + - PCGUARD - our own pcgard based instrumentation (default) - None of the following options are necessary to be used and are rather for - manual use (which only ever the author of this LTO implementation will use). - These are used if several separated instrumentations are performed which - are then later combined. +#### CMPLOG - - `AFL_LLVM_DOCUMENT_IDS=file` will document to a file which edge ID was given - to which function. This helps to identify functions with variable bytes - or which functions were touched by an input. - - `AFL_LLVM_MAP_ADDR` sets the fixed map address to a different address than - the default `0x10000`. A value of 0 or empty sets the map address to be - dynamic (the original AFL way, which is slower) - - `AFL_LLVM_MAP_DYNAMIC` sets the shared memory address to be dynamic - - `AFL_LLVM_LTO_STARTID` sets the starting location ID for the instrumentation. - This defaults to 1 - - `AFL_LLVM_LTO_DONTWRITEID` prevents that the highest location ID written - into the instrumentation is set in a global variable +Setting `AFL_LLVM_CMPLOG=1` during compilation will tell afl-clang-fast to +produce a CmpLog binary. - See [instrumentation/README.lto.md](../instrumentation/README.lto.md) for more information. +For more information, see +[instrumentation/README.cmplog.md](../instrumentation/README.cmplog.md). -### NGRAM +#### CTX - - Setting `AFL_LLVM_NGRAM_SIZE` or `AFL_LLVM_INSTRUMENT=NGRAM-{value}` - activates ngram prev_loc coverage, good values are 2, 4 or 8 - (any value between 2 and 16 is valid). - It is highly recommended to increase the `MAP_SIZE_POW2` definition in - config.h to at least 18 and maybe up to 20 for this as otherwise too - many map collisions occur. +Setting `AFL_LLVM_CTX` or `AFL_LLVM_INSTRUMENT=CTX` activates context sensitive +branch coverage - meaning that each edge is additionally combined with its +caller. It is highly recommended to increase the `MAP_SIZE_POW2` definition in +config.h to at least 18 and maybe up to 20 for this as otherwise too many map +collisions occur. - See [instrumentation/README.ngram.md](../instrumentation/README.ngram.md) +For more information, see +[instrumentation/README.ctx.md](../instrumentation/README.ctx.md). -### CTX +#### INSTRUMENT LIST (selectively instrument files and functions) - - Setting `AFL_LLVM_CTX` or `AFL_LLVM_INSTRUMENT=CTX` - activates context sensitive branch coverage - meaning that each edge - is additionally combined with its caller. - It is highly recommended to increase the `MAP_SIZE_POW2` definition in - config.h to at least 18 and maybe up to 20 for this as otherwise too - many map collisions occur. +This feature allows selective instrumentation of the source. - See [instrumentation/README.ctx.md](../instrumentation/README.ctx.md) +Setting `AFL_LLVM_ALLOWLIST` or `AFL_LLVM_DENYLIST` with a file name and/or +function will only instrument (or skip) those files that match the names listed +in the specified file. -### LAF-INTEL +For more information, see +[instrumentation/README.instrument_list.md](../instrumentation/README.instrument_list.md). - This great feature will split compares into series of single byte comparisons - to allow afl-fuzz to find otherwise rather impossible paths. It is not - restricted to Intel CPUs ;-) +#### LAF-INTEL - - Setting `AFL_LLVM_LAF_TRANSFORM_COMPARES` will split string compare functions +This great feature will split compares into series of single byte comparisons to +allow afl-fuzz to find otherwise rather impossible paths. It is not restricted +to Intel CPUs. ;-) - - Setting `AFL_LLVM_LAF_SPLIT_SWITCHES` will split all `switch` constructs + - Setting `AFL_LLVM_LAF_TRANSFORM_COMPARES` will split string compare + functions. - - Setting `AFL_LLVM_LAF_SPLIT_COMPARES` will split all floating point and - 64, 32 and 16 bit integer CMP instructions + - Setting `AFL_LLVM_LAF_SPLIT_COMPARES` will split all floating point and 64, + 32 and 16 bit integer CMP instructions. - - Setting `AFL_LLVM_LAF_SPLIT_FLOATS` will split floating points, needs - AFL_LLVM_LAF_SPLIT_COMPARES to be set + - Setting `AFL_LLVM_LAF_SPLIT_FLOATS` will split floating points, needs + `AFL_LLVM_LAF_SPLIT_COMPARES` to be set. - - Setting `AFL_LLVM_LAF_ALL` sets all of the above + - Setting `AFL_LLVM_LAF_SPLIT_SWITCHES` will split all `switch` constructs. - See [instrumentation/README.laf-intel.md](../instrumentation/README.laf-intel.md) for more information. + - Setting `AFL_LLVM_LAF_ALL` sets all of the above. -### INSTRUMENT LIST (selectively instrument files and functions) +For more information, see +[instrumentation/README.laf-intel.md](../instrumentation/README.laf-intel.md). - This feature allows selective instrumentation of the source +#### LTO - - Setting `AFL_LLVM_ALLOWLIST` or `AFL_LLVM_DENYLIST` with a filenames and/or - function will only instrument (or skip) those files that match the names - listed in the specified file. +This is a different way of instrumentation: first it compiles all code in LTO +(link time optimization) and then performs an edge inserting instrumentation +which is 100% collision free (collisions are a big issue in AFL and AFL-like +instrumentations). This is performed by using afl-clang-lto/afl-clang-lto++ +instead of afl-clang-fast, but is only built if LLVM 11 or newer is used. - See [instrumentation/README.instrument_list.md](../instrumentation/README.instrument_list.md) for more information. +`AFL_LLVM_INSTRUMENT=CFG` will use Control Flow Graph instrumentation. (Not +recommended for afl-clang-fast, default for afl-clang-lto as there it is a +different and better kind of instrumentation.) -### Thread safe instrumentation counters (in all modes) +None of the following options are necessary to be used and are rather for manual +use (which only ever the author of this LTO implementation will use). These are +used if several separated instrumentations are performed which are then later +combined. - - Setting `AFL_LLVM_THREADSAFE_INST` will inject code that implements thread - safe counters. The overhead is a little bit higher compared to the older - non-thread safe case. Note that this disables neverzero (see below). + - `AFL_LLVM_DOCUMENT_IDS=file` will document to a file which edge ID was given + to which function. This helps to identify functions with variable bytes or + which functions were touched by an input. + - `AFL_LLVM_LTO_DONTWRITEID` prevents that the highest location ID written + into the instrumentation is set in a global variable. + - `AFL_LLVM_LTO_STARTID` sets the starting location ID for the + instrumentation. This defaults to 1. + - `AFL_LLVM_MAP_ADDR` sets the fixed map address to a different address than + the default `0x10000`. A value of 0 or empty sets the map address to be + dynamic (the original AFL way, which is slower). + - `AFL_LLVM_MAP_DYNAMIC` sets the shared memory address to be dynamic. -### NOT_ZERO + For more information, see + [instrumentation/README.lto.md](../instrumentation/README.lto.md). - - Setting `AFL_LLVM_NOT_ZERO=1` during compilation will use counters - that skip zero on overflow. This is the default for llvm >= 9, - however for llvm versions below that this will increase an unnecessary - slowdown due a performance issue that is only fixed in llvm 9+. - This feature increases path discovery by a little bit. +#### NGRAM - - Setting `AFL_LLVM_SKIP_NEVERZERO=1` will not implement the skip zero - test. If the target performs only few loops then this will give a - small performance boost. +Setting `AFL_LLVM_INSTRUMENT=NGRAM-{value}` or `AFL_LLVM_NGRAM_SIZE` activates +ngram prev_loc coverage. Good values are 2, 4, or 8 (any value between 2 and 16 +is valid). It is highly recommended to increase the `MAP_SIZE_POW2` definition +in config.h to at least 18 and maybe up to 20 for this as otherwise too many map +collisions occur. - See [instrumentation/README.neverzero.md](../instrumentation/README.neverzero.md) +For more information, see +[instrumentation/README.ngram.md](../instrumentation/README.ngram.md). -### CMPLOG +#### NOT_ZERO - - Setting `AFL_LLVM_CMPLOG=1` during compilation will tell afl-clang-fast to - produce a CmpLog binary. + - Setting `AFL_LLVM_NOT_ZERO=1` during compilation will use counters that skip + zero on overflow. This is the default for llvm >= 9, however, for llvm + versions below that this will increase an unnecessary slowdown due a + performance issue that is only fixed in llvm 9+. This feature increases path + discovery by a little bit. - See [instrumentation/README.cmplog.md](../instrumentation/README.cmplog.md) + - Setting `AFL_LLVM_SKIP_NEVERZERO=1` will not implement the skip zero test. + If the target performs only a few loops, then this will give a small + performance boost. + +For more information, see +[instrumentation/README.neverzero.md](../instrumentation/README.neverzero.md). + +#### Thread safe instrumentation counters (in all modes) + +Setting `AFL_LLVM_THREADSAFE_INST` will inject code that implements thread safe +counters. The overhead is a little bit higher compared to the older non-thread +safe case. Note that this disables neverzero (see NOT_ZERO). ## 3) Settings for GCC / GCC_PLUGIN modes -Then there are a few specific features that are only available in GCC and -GCC_PLUGIN mode. +There are a few specific features that are only available in GCC and GCC_PLUGIN +mode. + + - GCC mode only: Setting `AFL_KEEP_ASSEMBLY` prevents afl-as from deleting + instrumented assembly files. Useful for troubleshooting problems or + understanding how the tool works. - - Setting `AFL_KEEP_ASSEMBLY` prevents afl-as from deleting instrumented - assembly files. Useful for troubleshooting problems or understanding how - the tool works. (GCC mode only) To get them in a predictable place, try something like: -``` + + ``` mkdir assembly_here TMPDIR=$PWD/assembly_here AFL_KEEP_ASSEMBLY=1 make clean all -``` - - Setting `AFL_GCC_INSTRUMENT_FILE` with a filename will only instrument those - files that match the names listed in this file (one filename per line). - See [instrumentation/README.instrument_list.md](../instrumentation/README.instrument_list.md) for more information. - (GCC_PLUGIN mode only) + ``` + + - GCC_PLUGIN mode only: Setting `AFL_GCC_INSTRUMENT_FILE` with a filename will + only instrument those files that match the names listed in this file (one + filename per line). See + [instrumentation/README.instrument_list.md](../instrumentation/README.instrument_list.md) + for more information. ## 4) Settings for afl-fuzz The main fuzzer binary accepts several options that disable a couple of sanity checks or alter some of the more exotic semantics of the tool: - - Setting `AFL_SKIP_CPUFREQ` skips the check for CPU scaling policy. This is - useful if you can't change the defaults (e.g., no root access to the - system) and are OK with some performance loss. + - Setting `AFL_AUTORESUME` will resume a fuzz run (same as providing `-i -`) + for an existing out folder, even if a different `-i` was provided. Without + this setting, afl-fuzz will refuse execution for a long-fuzzed out dir. - - `AFL_EXIT_WHEN_DONE` causes afl-fuzz to terminate when all existing paths - have been fuzzed and there were no new finds for a while. This would be - normally indicated by the cycle counter in the UI turning green. May be - convenient for some types of automated jobs. + - Benchmarking only: `AFL_BENCH_JUST_ONE` causes the fuzzer to exit after + processing the first queue entry; and `AFL_BENCH_UNTIL_CRASH` causes it to + exit soon after the first crash is found. - - `AFL_EXIT_ON_TIME` Causes afl-fuzz to terminate if no new paths were - found within a specified period of time (in seconds). May be convenient - for some types of automated jobs. + - `AFL_CMPLOG_ONLY_NEW` will only perform the expensive cmplog feature for + newly found testcases and not for testcases that are loaded on startup (`-i + in`). This is an important feature to set when resuming a fuzzing session. - - `AFL_EXIT_ON_SEED_ISSUES` will restore the vanilla afl-fuzz behaviour - which does not allow crashes or timeout seeds in the initial -i corpus. + - Setting `AFL_CRASH_EXITCODE` sets the exit code AFL treats as crash. For + example, if `AFL_CRASH_EXITCODE='-1'` is set, each input resulting in a `-1` + return code (i.e. `exit(-1)` got called), will be treated as if a crash had + occurred. This may be beneficial if you look for higher-level faulty + conditions in which your target still exits gracefully. - - `AFL_MAP_SIZE` sets the size of the shared map that afl-fuzz, afl-showmap, - afl-tmin and afl-analyze create to gather instrumentation data from - the target. This must be equal or larger than the size the target was - compiled with. + - Setting `AFL_CUSTOM_MUTATOR_LIBRARY` to a shared library with + afl_custom_fuzz() creates additional mutations through this library. If + afl-fuzz is compiled with Python (which is autodetected during building + afl-fuzz), setting `AFL_PYTHON_MODULE` to a Python module can also provide + additional mutations. If `AFL_CUSTOM_MUTATOR_ONLY` is also set, all + mutations will solely be performed with the custom mutator. This feature + allows to configure custom mutators which can be very helpful, e.g. fuzzing + XML or other highly flexible structured input. Please see + [custom_mutators.md](custom_mutators.md). - - `AFL_CMPLOG_ONLY_NEW` will only perform the expensive cmplog feature for - newly found testcases and not for testcases that are loaded on startup - (`-i in`). This is an important feature to set when resuming a fuzzing - session. + - Setting `AFL_CYCLE_SCHEDULES` will switch to a different schedule every time + a cycle is finished. - - `AFL_TESTCACHE_SIZE` allows you to override the size of `#define TESTCASE_CACHE` - in config.h. Recommended values are 50-250MB - or more if your fuzzing - finds a huge amount of paths for large inputs. + - Setting `AFL_DEBUG_CHILD` will not suppress the child output. This lets you + see all output of the child, making setup issues obvious. For example, in an + unicornafl harness, you might see python stacktraces. You may also see other + logs that way, indicating why the forkserver won't start. Not pretty but + good for debugging purposes. Note that `AFL_DEBUG_CHILD_OUTPUT` is + deprecated. - Setting `AFL_DISABLE_TRIM` tells afl-fuzz not to trim test cases. This is usually a bad idea! - - Setting `AFL_NO_AFFINITY` disables attempts to bind to a specific CPU core - on Linux systems. This slows things down, but lets you run more instances - of afl-fuzz than would be prudent (if you really want to). + - `AFL_EXIT_ON_SEED_ISSUES` will restore the vanilla afl-fuzz behaviour which + does not allow crashes or timeout seeds in the initial -i corpus. - - Setting `AFL_TRY_AFFINITY` tries to attempt binding to a specific CPU core - on Linux systems, but will not terminate if that fails. + - `AFL_EXIT_ON_TIME` causes afl-fuzz to terminate if no new paths were found + within a specified period of time (in seconds). May be convenient for some + types of automated jobs. - - Setting `AFL_NO_AUTODICT` will not load an LTO generated auto dictionary - that is compiled into the target. + - `AFL_EXIT_WHEN_DONE` causes afl-fuzz to terminate when all existing paths + have been fuzzed and there were no new finds for a while. This would be + normally indicated by the cycle counter in the UI turning green. May be + convenient for some types of automated jobs. - - Setting `AFL_HANG_TMOUT` allows you to specify a different timeout for - deciding if a particular test case is a "hang". The default is 1 second - or the value of the `-t` parameter, whichever is larger. Dialing the value - down can be useful if you are very concerned about slow inputs, or if you - don't want AFL++ to spend too much time classifying that stuff and just - rapidly put all timeouts in that bin. + - Setting `AFL_EXPAND_HAVOC_NOW` will start in the extended havoc mode that + includes costly mutations. afl-fuzz automatically enables this mode when + deemed useful otherwise. + + - `AFL_FAST_CAL` keeps the calibration stage about 2.5x faster (albeit less + precise), which can help when starting a session against a slow target. + `AFL_CAL_FAST` works too. + + - Setting `AFL_FORCE_UI` will force painting the UI on the screen even if no + valid terminal was detected (for virtual consoles). - Setting `AFL_FORKSRV_INIT_TMOUT` allows you to specify a different timeout to wait for the forkserver to spin up. The default is the `-t` value times `FORK_WAIT_MULT` from `config.h` (usually 10), so for a `-t 100`, the - default would wait for `1000` milliseconds. Setting a different time here is useful - if the target has a very slow startup time, for example when doing - full-system fuzzing or emulation, but you don't want the actual runs - to wait too long for timeouts. - - - `AFL_NO_ARITH` causes AFL++ to skip most of the deterministic arithmetics. - This can be useful to speed up the fuzzing of text-based file formats. + default would wait for `1000` milliseconds. Setting a different time here is + useful if the target has a very slow startup time, for example, when doing + full-system fuzzing or emulation, but you don't want the actual runs to wait + too long for timeouts. - - `AFL_NO_SNAPSHOT` will advice afl-fuzz not to use the snapshot feature - if the snapshot lkm is loaded - - - `AFL_SHUFFLE_QUEUE` randomly reorders the input queue on startup. Requested - by some users for unorthodox parallelized fuzzing setups, but not - advisable otherwise. + - Setting `AFL_HANG_TMOUT` allows you to specify a different timeout for + deciding if a particular test case is a "hang". The default is 1 second or + the value of the `-t` parameter, whichever is larger. Dialing the value down + can be useful if you are very concerned about slow inputs, or if you don't + want AFL++ to spend too much time classifying that stuff and just rapidly + put all timeouts in that bin. - - `AFL_TMPDIR` is used to write the `.cur_input` file to if exists, and in - the normal output directory otherwise. You would use this to point to - a ramdisk/tmpfs. This increases the speed by a small value but also - reduces the stress on SSDs. + - If you are Jakub, you may need `AFL_I_DONT_CARE_ABOUT_MISSING_CRASHES`. + Others need not apply, unless they also want to disable the + `/proc/sys/kernel/core_pattern` check. - - When developing custom instrumentation on top of afl-fuzz, you can use - `AFL_SKIP_BIN_CHECK` to inhibit the checks for non-instrumented binaries - and shell scripts; and `AFL_DUMB_FORKSRV` in conjunction with the `-n` - setting to instruct afl-fuzz to still follow the fork server protocol - without expecting any instrumentation data in return. - Note that this also turns off auto map size detection. + - If afl-fuzz encounters an incorrect fuzzing setup during a fuzzing session + (not at startup), it will terminate. If you do not want this, then you can + set `AFL_IGNORE_PROBLEMS`. - When running in the `-M` or `-S` mode, setting `AFL_IMPORT_FIRST` causes the - fuzzer to import test cases from other instances before doing anything - else. This makes the "own finds" counter in the UI more accurate. - Beyond counter aesthetics, not much else should change. + fuzzer to import test cases from other instances before doing anything else. + This makes the "own finds" counter in the UI more accurate. Beyond counter + aesthetics, not much else should change. + + - `AFL_KILL_SIGNAL`: Set the signal ID to be delivered to child processes on + timeout. Unless you implement your own targets or instrumentation, you + likely don't have to set it. By default, on timeout and on exit, `SIGKILL` + (`AFL_KILL_SIGNAL=9`) will be delivered to the child. + + - `AFL_MAP_SIZE` sets the size of the shared map that afl-analyze, afl-fuzz, + afl-showmap, and afl-tmin create to gather instrumentation data from the + target. This must be equal or larger than the size the target was compiled + with. + + - Setting `AFL_MAX_DET_EXRAS` will change the threshold at what number of + elements in the `-x` dictionary and LTO autodict (combined) the + probabilistic mode will kick off. In probabilistic mode, not all dictionary + entries will be used all of the time for fuzzing mutations to not slow down + fuzzing. The default count is `200` elements. So for the 200 + 1st element, + there is a 1 in 201 chance, that one of the dictionary entries will not be + used directly. - - Note that `AFL_POST_LIBRARY` is deprecated, use `AFL_CUSTOM_MUTATOR_LIBRARY` - instead (see below). + - Setting `AFL_NO_AFFINITY` disables attempts to bind to a specific CPU core + on Linux systems. This slows things down, but lets you run more instances of + afl-fuzz than would be prudent (if you really want to). - - `AFL_KILL_SIGNAL`: Set the signal ID to be delivered to child processes on timeout. - Unless you implement your own targets or instrumentation, you likely don't have to set it. - By default, on timeout and on exit, `SIGKILL` (`AFL_KILL_SIGNAL=9`) will be delivered to the child. + - `AFL_NO_ARITH` causes AFL++ to skip most of the deterministic arithmetics. + This can be useful to speed up the fuzzing of text-based file formats. - - Setting `AFL_CUSTOM_MUTATOR_LIBRARY` to a shared library with - afl_custom_fuzz() creates additional mutations through this library. - If afl-fuzz is compiled with Python (which is autodetected during building - afl-fuzz), setting `AFL_PYTHON_MODULE` to a Python module can also provide - additional mutations. - If `AFL_CUSTOM_MUTATOR_ONLY` is also set, all mutations will solely be - performed with the custom mutator. - This feature allows to configure custom mutators which can be very helpful, - e.g. fuzzing XML or other highly flexible structured input. - Please see [custom_mutators.md](custom_mutators.md). + - Setting `AFL_NO_AUTODICT` will not load an LTO generated auto dictionary + that is compiled into the target. - - `AFL_FAST_CAL` keeps the calibration stage about 2.5x faster (albeit less - precise), which can help when starting a session against a slow target. - `AFL_CAL_FAST` works too. + - Setting `AFL_NO_COLOR` or `AFL_NO_COLOUR` will omit control sequences for + coloring console output when configured with USE_COLOR and not + ALWAYS_COLORED. - The CPU widget shown at the bottom of the screen is fairly simplistic and may complain of high load prematurely, especially on systems with low core - counts. To avoid the alarming red color, you can set `AFL_NO_CPU_RED`. - - - In QEMU mode (-Q) and Frida mode (-O), `AFL_PATH` will - be searched for afl-qemu-trace and afl-frida-trace.so. - - - In QEMU mode (-Q), setting `AFL_QEMU_CUSTOM_BIN` cause afl-fuzz to skip - prepending `afl-qemu-trace` to your command line. Use this if you wish to use a - custom afl-qemu-trace or if you need to modify the afl-qemu-trace arguments. + counts. To avoid the alarming red color for very high CPU usages, you can + set `AFL_NO_CPU_RED`. - - Setting `AFL_CYCLE_SCHEDULES` will switch to a different schedule everytime - a cycle is finished. - - - Setting `AFL_EXPAND_HAVOC_NOW` will start in the extended havoc mode that - includes costly mutations. afl-fuzz automatically enables this mode when - deemed useful otherwise. + - Setting `AFL_NO_FORKSRV` disables the forkserver optimization, reverting to + fork + execve() call for every tested input. This is useful mostly when + working with unruly libraries that create threads or do other crazy things + when initializing (before the instrumentation has a chance to run). - - Setting `AFL_PRELOAD` causes AFL++ to set `LD_PRELOAD` for the target binary - without disrupting the afl-fuzz process itself. This is useful, among other - things, for bootstrapping libdislocator.so. + Note that this setting inhibits some of the user-friendly diagnostics + normally done when starting up the forkserver and causes a pretty + significant performance drop. - - Setting `AFL_TARGET_ENV` causes AFL++ to set extra environment variables - for the target binary. Example: `AFL_TARGET_ENV="VAR1=1 VAR2='a b c'" afl-fuzz ... ` - This exists mostly for things like `LD_LIBRARY_PATH` but it would theoretically - allow fuzzing of AFL++ itself (with 'target' AFL++ using some AFL_ vars that - would disrupt work of 'fuzzer' AFL++). + - `AFL_NO_SNAPSHOT` will advice afl-fuzz not to use the snapshot feature if + the snapshot lkm is loaded. - - Setting `AFL_NO_UI` inhibits the UI altogether, and just periodically prints + - Setting `AFL_NO_UI` inhibits the UI altogether and just periodically prints some basic stats. This behavior is also automatically triggered when the output from afl-fuzz is redirected to a file or to a pipe. - - Setting `AFL_NO_COLOR` or `AFL_NO_COLOUR` will omit control sequences for - coloring console output when configured with USE_COLOR and not ALWAYS_COLORED. - - - Setting `AFL_FORCE_UI` will force painting the UI on the screen even if - no valid terminal was detected (for virtual consoles) + - In QEMU mode (-Q) and Frida mode (-O), `AFL_PATH` will be searched for + afl-qemu-trace and afl-frida-trace.so. - - If you are using persistent mode (you should, see [instrumentation/README.persistent_mode.md](../instrumentation/README.persistent_mode.md)) + - If you are using persistent mode (you should, see + [instrumentation/README.persistent_mode.md](../instrumentation/README.persistent_mode.md)), some targets keep inherent state due which a detected crash testcase does not crash the target again when the testcase is given. To be able to still - re-trigger these crashes you can use the `AFL_PERSISTENT_RECORD` variable - with a value of how many previous fuzz cases to keep prio a crash. - if set to e.g. 10, then the 9 previous inputs are written to - out/default/crashes as RECORD:000000,cnt:000000 to RECORD:000000,cnt:000008 - and RECORD:000000,cnt:000009 being the crash case. - NOTE: This option needs to be enabled in config.h first! + re-trigger these crashes, you can use the `AFL_PERSISTENT_RECORD` variable + with a value of how many previous fuzz cases to keep prio a crash. If set to + e.g. 10, then the 9 previous inputs are written to out/default/crashes as + RECORD:000000,cnt:000000 to RECORD:000000,cnt:000008 and + RECORD:000000,cnt:000009 being the crash case. NOTE: This option needs to be + enabled in config.h first! - - If afl-fuzz encounters an incorrect fuzzing setup during a fuzzing session - (not at startup), it will terminate. If you do not want this then you can - set `AFL_IGNORE_PROBLEMS`. - - - If you are Jakub, you may need `AFL_I_DONT_CARE_ABOUT_MISSING_CRASHES`. - Others need not apply, unless they also want to disable the - `/proc/sys/kernel/core_pattern` check. - - - Benchmarking only: `AFL_BENCH_JUST_ONE` causes the fuzzer to exit after - processing the first queue entry; and `AFL_BENCH_UNTIL_CRASH` causes it to - exit soon after the first crash is found. - - - Setting `AFL_DEBUG_CHILD` will not suppress the child output. - This lets you see all output of the child, making setup issues obvious. - For example, in an unicornafl harness, you might see python stacktraces. - You may also see other logs that way, indicating why the forkserver won't start. - Not pretty but good for debugging purposes. - Note that `AFL_DEBUG_CHILD_OUTPUT` is deprecated. + - Note that `AFL_POST_LIBRARY` is deprecated, use `AFL_CUSTOM_MUTATOR_LIBRARY` + instead. - - Setting `AFL_NO_CPU_RED` will not display very high cpu usages in red color. + - Setting `AFL_PRELOAD` causes AFL++ to set `LD_PRELOAD` for the target binary + without disrupting the afl-fuzz process itself. This is useful, among other + things, for bootstrapping libdislocator.so. - - Setting `AFL_AUTORESUME` will resume a fuzz run (same as providing `-i -`) - for an existing out folder, even if a different `-i` was provided. - Without this setting, afl-fuzz will refuse execution for a long-fuzzed out dir. + - In QEMU mode (-Q), setting `AFL_QEMU_CUSTOM_BIN` will cause afl-fuzz to skip + prepending `afl-qemu-trace` to your command line. Use this if you wish to + use a custom afl-qemu-trace or if you need to modify the afl-qemu-trace + arguments. - - Setting `AFL_MAX_DET_EXRAS` will change the threshold at what number of elements - in the `-x` dictionary and LTO autodict (combined) the probabilistic mode will - kick off. In probabilistic mode, not all dictionary entries will be used all - of the time for fuzzing mutations to not slow down fuzzing. - The default count is `200` elements. So for the 200 + 1st element, there is a - 1 in 201 chance, that one of the dictionary entries will not be used directly. + - `AFL_SHUFFLE_QUEUE` randomly reorders the input queue on startup. Requested + by some users for unorthodox parallelized fuzzing setups, but not advisable + otherwise. - - Setting `AFL_NO_FORKSRV` disables the forkserver optimization, reverting to - fork + execve() call for every tested input. This is useful mostly when - working with unruly libraries that create threads or do other crazy - things when initializing (before the instrumentation has a chance to run). + - When developing custom instrumentation on top of afl-fuzz, you can use + `AFL_SKIP_BIN_CHECK` to inhibit the checks for non-instrumented binaries and + shell scripts; and `AFL_DUMB_FORKSRV` in conjunction with the `-n` setting + to instruct afl-fuzz to still follow the fork server protocol without + expecting any instrumentation data in return. Note that this also turns off + auto map size detection. - Note that this setting inhibits some of the user-friendly diagnostics - normally done when starting up the forkserver and causes a pretty - significant performance drop. + - Setting `AFL_SKIP_CPUFREQ` skips the check for CPU scaling policy. This is + useful if you can't change the defaults (e.g., no root access to the system) + and are OK with some performance loss. + + - Setting `AFL_STATSD` enables StatsD metrics collection. By default, AFL++ + will send these metrics over UDP to 127.0.0.1:8125. The host and port are + configurable with `AFL_STATSD_HOST` and `AFL_STATSD_PORT` respectively. To + enable tags (banner and afl_version), you should provide + `AFL_STATSD_TAGS_FLAVOR` that matches your StatsD server (see + `AFL_STATSD_TAGS_FLAVOR`). + + - Setting `AFL_STATSD_TAGS_FLAVOR` to one of `dogstatsd`, `influxdb`, + `librato`, or `signalfx` allows you to add tags to your fuzzing instances. + This is especially useful when running multiple instances (`-M/-S` for + example). Applied tags are `banner` and `afl_version`. `banner` corresponds + to the name of the fuzzer provided through `-M/-S`. `afl_version` + corresponds to the currently running AFL version (e.g. `++3.0c`). Default + (empty/non present) will add no tags to the metrics. For more information, + see [rpc_statsd.md](rpc_statsd.md). + + - Setting `AFL_TARGET_ENV` causes AFL++ to set extra environment variables for + the target binary. Example: `AFL_TARGET_ENV="VAR1=1 VAR2='a b c'" afl-fuzz + ... `. This exists mostly for things like `LD_LIBRARY_PATH` but it would + theoretically allow fuzzing of AFL++ itself (with 'target' AFL++ using some + AFL_ vars that would disrupt work of 'fuzzer' AFL++). + + - `AFL_TESTCACHE_SIZE` allows you to override the size of `#define + TESTCASE_CACHE` in config.h. Recommended values are 50-250MB - or more if + your fuzzing finds a huge amount of paths for large inputs. + + - `AFL_TMPDIR` is used to write the `.cur_input` file to if it exists, and in + the normal output directory otherwise. You would use this to point to a + ramdisk/tmpfs. This increases the speed by a small value but also reduces + the stress on SSDs. - - Setting `AFL_STATSD` enables StatsD metrics collection. - By default AFL++ will send these metrics over UDP to 127.0.0.1:8125. - The host and port are configurable with `AFL_STATSD_HOST` and `AFL_STATSD_PORT` respectively. - To enable tags (banner and afl_version) you should provide `AFL_STATSD_TAGS_FLAVOR` that matches - your StatsD server (see `AFL_STATSD_TAGS_FLAVOR`) - - - Setting `AFL_STATSD_TAGS_FLAVOR` to one of `dogstatsd`, `librato`, `signalfx` or `influxdb` - allows you to add tags to your fuzzing instances. This is especially useful when running - multiple instances (`-M/-S` for example). Applied tags are `banner` and `afl_version`. - `banner` corresponds to the name of the fuzzer provided through `-M/-S`. - `afl_version` corresponds to the currently running AFL version (e.g `++3.0c`). - Default (empty/non present) will add no tags to the metrics. - See [rpc_statsd.md](rpc_statsd.md) for more information. - - - Setting `AFL_CRASH_EXITCODE` sets the exit code AFL treats as crash. - For example, if `AFL_CRASH_EXITCODE='-1'` is set, each input resulting - in an `-1` return code (i.e. `exit(-1)` got called), will be treated - as if a crash had ocurred. - This may be beneficial if you look for higher-level faulty conditions in which your - target still exits gracefully. + - Setting `AFL_TRY_AFFINITY` tries to attempt binding to a specific CPU core + on Linux systems, but will not terminate if that fails. - Outdated environment variables that are not supported anymore: - `AFL_DEFER_FORKSRV` - `AFL_PERSISTENT` + - `AFL_DEFER_FORKSRV` + - `AFL_PERSISTENT` ## 5) Settings for afl-qemu-trace The QEMU wrapper used to instrument binary-only code supports several settings: - - It is possible to set `AFL_INST_RATIO` to skip the instrumentation on some - of the basic blocks, which can be useful when dealing with very complex - binaries. - - - Setting `AFL_INST_LIBS` causes the translator to also instrument the code - inside any dynamically linked libraries (notably including glibc). - - Setting `AFL_COMPCOV_LEVEL` enables the CompareCoverage tracing of all cmp and sub in x86 and x86_64 and memory comparions functions (e.g. strcmp, - memcmp, ...) when libcompcov is preloaded using `AFL_PRELOAD`. - More info at qemu_mode/libcompcov/README.md. + memcmp, ...) when libcompcov is preloaded using `AFL_PRELOAD`. More info at + [qemu_mode/libcompcov/README.md](../qemu_mode/libcompcov/README.md). + There are two levels at the moment, `AFL_COMPCOV_LEVEL=1` that instruments only comparisons with immediate values / read-only memory and `AFL_COMPCOV_LEVEL=2` that instruments all the comparions. Level 2 is more accurate but may need a larger shared memory. - - Setting `AFL_QEMU_COMPCOV` enables the CompareCoverage tracing of all - cmp and sub in x86 and x86_64. - This is an alias of `AFL_COMPCOV_LEVEL=1` when `AFL_COMPCOV_LEVEL` is - not specified. + - `AFL_DEBUG` will print the found entrypoint for the binary to stderr. Use + this if you are unsure if the entrypoint might be wrong - but use it + directly, e.g. `afl-qemu-trace ./program`. - - The underlying QEMU binary will recognize any standard "user space - emulation" variables (e.g., `QEMU_STACK_SIZE`), but there should be no - reason to touch them. + - `AFL_ENTRYPOINT` allows you to specify a specific entrypoint into the binary + (this can be very good for the performance!). The entrypoint is specified as + hex address, e.g. `0x4004110`. Note that the address must be the address of + a basic block. + + - Setting `AFL_INST_LIBS` causes the translator to also instrument the code + inside any dynamically linked libraries (notably including glibc). + + - It is possible to set `AFL_INST_RATIO` to skip the instrumentation on some + of the basic blocks, which can be useful when dealing with very complex + binaries. - - `AFL_DEBUG` will print the found entrypoint for the binary to stderr. - Use this if you are unsure if the entrypoint might be wrong - but - use it directly, e.g. `afl-qemu-trace ./program` + - Setting `AFL_QEMU_COMPCOV` enables the CompareCoverage tracing of all cmp + and sub in x86 and x86_64. This is an alias of `AFL_COMPCOV_LEVEL=1` when + `AFL_COMPCOV_LEVEL` is not specified. - - `AFL_ENTRYPOINT` allows you to specify a specific entrypoint into the - binary (this can be very good for the performance!). - The entrypoint is specified as hex address, e.g. `0x4004110` - Note that the address must be the address of a basic block. + - With `AFL_QEMU_FORCE_DFL` you force QEMU to ignore the registered signal + handlers of the target. - - When the target is i386/x86_64 you can specify the address of the function + - When the target is i386/x86_64, you can specify the address of the function that has to be the body of the persistent loop using `AFL_QEMU_PERSISTENT_ADDR=start addr`. - - Another modality to execute the persistent loop is to specify also the - `AFL_QEMU_PERSISTENT_RET=end addr` env variable. - With this variable assigned, instead of patching the return address, the - specified instruction is transformed to a jump towards `start addr`. + - With `AFL_QEMU_PERSISTENT_GPR=1` QEMU will save the original value of + general purpose registers and restore them in each persistent cycle. - - `AFL_QEMU_PERSISTENT_GPR=1` QEMU will save the original value of general - purpose registers and restore them in each persistent cycle. + - Another modality to execute the persistent loop is to specify also the + `AFL_QEMU_PERSISTENT_RET=end addr` env variable. With this variable + assigned, instead of patching the return address, the specified instruction + is transformed to a jump towards `start addr`. - - With `AFL_QEMU_PERSISTENT_RETADDR_OFFSET` you can specify the offset from the - stack pointer in which QEMU can find the return address when `start addr` is - hit. + - With `AFL_QEMU_PERSISTENT_RETADDR_OFFSET` you can specify the offset from + the stack pointer in which QEMU can find the return address when `start + addr` is hit. - With `AFL_USE_QASAN` you can enable QEMU AddressSanitizer for dynamically linked binaries. - - With `AFL_QEMU_FORCE_DFL` you force QEMU to ignore the registered signal - handlers of the target. + - The underlying QEMU binary will recognize any standard "user space + emulation" variables (e.g., `QEMU_STACK_SIZE`), but there should be no + reason to touch them. ## 6) Settings for afl-cmin The corpus minimization script offers very little customization: - - Setting `AFL_PATH` offers a way to specify the location of afl-showmap - and afl-qemu-trace (the latter only in `-Q` mode). + - `AFL_ALLOW_TMP` permits this and some other scripts to run in /tmp. This is + a modest security risk on multi-user systems with rogue users, but should be + safe on dedicated fuzzing boxes. - `AFL_KEEP_TRACES` makes the tool keep traces and other metadata used for minimization and normally deleted at exit. The files can be found in the `<out_dir>/.traces/` directory. - - `AFL_ALLOW_TMP` permits this and some other scripts to run in /tmp. This is - a modest security risk on multi-user systems with rogue users, but should - be safe on dedicated fuzzing boxes. + - Setting `AFL_PATH` offers a way to specify the location of afl-showmap and + afl-qemu-trace (the latter only in `-Q` mode). - `AFL_PRINT_FILENAMES` prints each filename to stdout, as it gets processed. - This can help when embedding `afl-cmin` or `afl-showmap` in other scripts scripting. + This can help when embedding `afl-cmin` or `afl-showmap` in other scripts. ## 7) Settings for afl-tmin @@ -594,25 +617,25 @@ of decimal. ## 9) Settings for libdislocator -The library honors these environmental variables: +The library honors these environment variables: - - `AFL_LD_LIMIT_MB` caps the size of the maximum heap usage permitted by the - library, in megabytes. The default value is 1 GB. Once this is exceeded, - allocations will return NULL. + - `AFL_ALIGNED_ALLOC=1` will force the alignment of the allocation size to + `max_align_t` to be compliant with the C standard. - `AFL_LD_HARD_FAIL` alters the behavior by calling `abort()` on excessive allocations, thus causing what AFL++ would perceive as a crash. Useful for programs that are supposed to maintain a specific memory footprint. - - `AFL_LD_VERBOSE` causes the library to output some diagnostic messages - that may be useful for pinpointing the cause of any observed issues. + - `AFL_LD_LIMIT_MB` caps the size of the maximum heap usage permitted by the + library, in megabytes. The default value is 1 GB. Once this is exceeded, + allocations will return NULL. - - `AFL_LD_NO_CALLOC_OVER` inhibits `abort()` on `calloc()` overflows. Most - of the common allocators check for that internally and return NULL, so - it's a security risk only in more exotic setups. + - `AFL_LD_NO_CALLOC_OVER` inhibits `abort()` on `calloc()` overflows. Most of + the common allocators check for that internally and return NULL, so it's a + security risk only in more exotic setups. - - `AFL_ALIGNED_ALLOC=1` will force the alignment of the allocation size to - `max_align_t` to be compliant with the C standard. + - `AFL_LD_VERBOSE` causes the library to output some diagnostic messages that + may be useful for pinpointing the cause of any observed issues. ## 10) Settings for libtokencap @@ -624,40 +647,44 @@ discovered tokens should be written. Several variables are not directly interpreted by afl-fuzz, but are set to optimal values if not already present in the environment: - - By default, `LD_BIND_NOW` is set to speed up fuzzing by forcing the - linker to do all the work before the fork server kicks in. You can - override this by setting `LD_BIND_LAZY` beforehand, but it is almost - certainly pointless. - - By default, `ASAN_OPTIONS` are set to (among others): -``` + + ``` abort_on_error=1 detect_leaks=0 malloc_context_size=0 symbolize=0 allocator_may_return_null=1 -``` - If you want to set your own options, be sure to include `abort_on_error=1` - - otherwise, the fuzzer will not be able to detect crashes in the tested - app. Similarly, include `symbolize=0`, since without it, AFL++ may have + ``` + + If you want to set your own options, be sure to include `abort_on_error=1` - + otherwise, the fuzzer will not be able to detect crashes in the tested app. + Similarly, include `symbolize=0`, since without it, AFL++ may have difficulty telling crashes and hangs apart. + - Similarly, the default `LSAN_OPTIONS` are set to: + + ``` + exit_code=23 + fast_unwind_on_malloc=0 + symbolize=0 + print_suppressions=0 + ``` + + Be sure to include the first ones for LSAN and MSAN when customizing + anything, since some MSAN and LSAN versions don't call `abort()` on error, + and we need a way to detect faults. + - In the same vein, by default, `MSAN_OPTIONS` are set to: -``` + + ``` exit_code=86 (required for legacy reasons) abort_on_error=1 symbolize=0 msan_track_origins=0 allocator_may_return_null=1 -``` - - Similarly, the default `LSAN_OPTIONS` are set to: -``` - exit_code=23 - fast_unwind_on_malloc=0 - symbolize=0 - print_suppressions=0 -``` - Be sure to include the first ones for LSAN and MSAN when customizing - anything, since some MSAN and LSAN versions don't call `abort()` on - error, and we need a way to detect faults. + ``` + - By default, `LD_BIND_NOW` is set to speed up fuzzing by forcing the linker + to do all the work before the fork server kicks in. You can override this by + setting `LD_BIND_LAZY` beforehand, but it is almost certainly pointless. \ No newline at end of file diff --git a/docs/features.md b/docs/features.md index c0956703..f44e32ff 100644 --- a/docs/features.md +++ b/docs/features.md @@ -4,20 +4,20 @@ with laf-intel and redqueen, frida mode, unicorn mode, gcc plugin, full *BSD, Mac OS, Solaris and Android support and much, much, much more. - | Feature/Instrumentation | afl-gcc | llvm | gcc_plugin | frida_mode | qemu_mode |unicorn_mode | - | -------------------------|:-------:|:---------:|:----------:|:----------------:|:----------------:|:----------------:| - | Threadsafe counters | | x(3) | | | | | - | NeverZero | x86[_64]| x(1) | x | x | x | x | - | Persistent Mode | | x | x | x86[_64]/arm64 | x86[_64]/arm[64] | x | - | LAF-Intel / CompCov | | x | | | x86[_64]/arm[64] | x86[_64]/arm[64] | - | CmpLog | | x | | x86[_64]/arm64 | x86[_64]/arm[64] | | - | Selective Instrumentation| | x | x | x | x | | - | Non-Colliding Coverage | | x(4) | | | (x)(5) | | - | Ngram prev_loc Coverage | | x(6) | | | | | - | Context Coverage | | x(6) | | | | | - | Auto Dictionary | | x(7) | | | | | - | Snapshot LKM Support | | (x)(8) | (x)(8) | | (x)(5) | | - | Shared Memory Testcases | | x | x | x86[_64]/arm64 | x | x | + | Feature/Instrumentation | afl-gcc | llvm | gcc_plugin | frida_mode(9) | qemu_mode(10) |unicorn_mode(10) |coresight_mode(11)| + | -------------------------|:-------:|:---------:|:----------:|:----------------:|:----------------:|:----------------:|:----------------:| + | Threadsafe counters | | x(3) | | | | | | + | NeverZero | x86[_64]| x(1) | x | x | x | x | | + | Persistent Mode | | x | x | x86[_64]/arm64 | x86[_64]/arm[64] | x | | + | LAF-Intel / CompCov | | x | | | x86[_64]/arm[64] | x86[_64]/arm[64] | | + | CmpLog | | x | | x86[_64]/arm64 | x86[_64]/arm[64] | | | + | Selective Instrumentation| | x | x | x | x | | | + | Non-Colliding Coverage | | x(4) | | | (x)(5) | | | + | Ngram prev_loc Coverage | | x(6) | | | | | | + | Context Coverage | | x(6) | | | | | | + | Auto Dictionary | | x(7) | | | | | | + | Snapshot LKM Support | | (x)(8) | (x)(8) | | (x)(5) | | | + | Shared Memory Testcases | | x | x | x86[_64]/arm64 | x | x | | 1. default for LLVM >= 9.0, env var for older version due an efficiency bug in previous llvm versions 2. GCC creates non-performant code, hence it is disabled in gcc_plugin @@ -27,6 +27,9 @@ 6. not compatible with LTO instrumentation and needs at least LLVM v4.1 7. automatic in LTO mode with LLVM 11 and newer, an extra pass for all LLVM versions that write to a file to use with afl-fuzz' `-x` 8. the snapshot LKM is currently unmaintained due to too many kernel changes coming too fast :-( + 9. frida mode is supported on Linux and MacOS for Intel and ARM + 10. QEMU/Unicorn is only supported on Linux + 11. Coresight mode is only available on AARCH64 Linux with a CPU with Coresight extension Among others, the following features and patches have been integrated: diff --git a/docs/technical_details.md b/docs/technical_details.md index b9d271d9..994ffe9f 100644 --- a/docs/technical_details.md +++ b/docs/technical_details.md @@ -1,7 +1,7 @@ # Technical "whitepaper" for afl-fuzz -NOTE: this document is rather outdated! +NOTE: this document is mostly outdated! This document provides a quick overview of the guts of American Fuzzy Lop. |