ExternalVendorCode/AFLplusplus
1
0
Fork 0
mirror of https://github.com/AFLplusplus/AFLplusplus.git synced 2025-06-13 02:28:09 +00:00
Code Issues Packages Projects Releases Wiki Activity

review, mark env variables, linkify

Browse Source
This commit is contained in:
hexcoder-
2020-10-30 14:37:06 +01:00
parent efd27bd8ce
commit dfb847a51b
1 changed files with 180 additions and 179 deletions
Download Patch File Download Diff File Expand all files Collapse all files

359
docs/env_variables.md
View File

@ -2,63 +2,64 @@
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 for the general
users or for some types of custom fuzzing setups. See [README.md](README.md) for the general
instruction manual.
## 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 --afl-MODE command line options to the compiler
2. use a symlink to afl-cc: afl-gcc, afl-g++, afl-clang, afl-clang++,
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. using the environment variable AFL_CC_COMPILER with MODE
3. or using the environment variable `AFL_CC_COMPILER` with `MODE`
MODE can one of LTO (afl-clang-lto*), LLVM (afl-clang-fast*), GCC_PLUGIN
(afl-g*-fast) or GCC (afl-gcc/afl-g++).
`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 beside the --afl-MODE command no afl specific command-line options
are accepted, the compile-time tools make fairly broad use of environmental
variables:
- Most afl tools do not print any ouput if stout/stderr are redirected.
If you want to have the output into a file then set the AFL_DEBUG
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:
- 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.
- 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
- 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.
- By default, the wrapper appends -O3 to optimize builds. Very rarely, this
will cause problems in programs built with -Werror, simply because -O3
- 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
overriden.
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
- Setting `AFL_USE_ASAN` automatically enables ASAN, provided that your
compiler supports that. Note that fuzzing with ASAN is mildly challenging
- see [notes_for_asan.md](notes_for_asan.md).
(You can also enable MSAN via AFL_USE_MSAN; ASAN and MSAN come with the
(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
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)
`AFL_USE_CFISAN=1`)
- Setting AFL_CC, AFL_CXX, and AFL_AS lets you use alternate downstream
- 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 $PATH.
in your `$PATH`.
- AFL_PATH can be used to point afl-gcc to an alternate location of afl-as.
- `AFL_PATH` can be used to point afl-gcc to an alternate location of afl-as.
One possible use of this is examples/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_INST_RATIO to a percentage between 0 and 100% controls the
- 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.
@ -66,51 +67,51 @@ variables:
(If this ever happens, afl-fuzz will warn you ahead of the time by
displaying the "bitmap density" field in fiery red.)
Setting AFL_INST_RATIO to 0 is a valid choice. This will instrument only
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.
- AFL_NO_BUILTIN causes the compiler to generate code suitable for use with
- `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).
- TMPDIR is used by afl-as for temporary files; if this variable is not set,
- `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
text files then use the `AFL_AS_FORCE_INSTRUMENT` variable:
`AFL_AS_FORCE_INSTRUMENT=1 afl-gcc foo.s -o foo`
- Setting AFL_QUIET will prevent afl-cc and afl-as banners from being
- Setting `AFL_QUIET` will prevent afl-cc and afl-as banners from being
displayed during compilation, in case you find them distracting.
- Setting AFL_CAL_FAST will speed up the initial calibration, if the
application is very slow
- Setting `AFL_CAL_FAST` will speed up the initial calibration, if the
application is very slow.
## 2) Settings for LLVM and LTO: afl-clang-fast / afl-clang-fast++ / afl-clang-lto / afl-clang-lto++
The native instrumentation helpers (instrumentation and gcc_plugin) accept a subset
of the settings discussed in section #1, with the exception of:
of the settings discussed in section 1, with the exception of:
- LLVM modes support `AFL_LLVM_DICT2FILE=/absolute/path/file.txt` which will
write all constant string comparisons to this file to be used 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.
- `AFL_AS`, since this toolchain does not directly invoke GNU as.
- TMPDIR and AFL_KEEP_ASSEMBLY, since no temporary assembly files are
- `TMPDIR` and `AFL_KEEP_ASSEMBLY`, since no temporary assembly files are
created.
- AFL_INST_RATIO, as we by default collision free instrumentation is used.
- `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:
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.
- `AFL_LLVM_INSTRUMENT` - this configures the instrumentation mode.
Available options:
CLASSIC - classic AFL (map[cur_loc ^ prev_loc >> 1]++) (default)
CFG - InsTrim instrumentation (see below)
@ -119,148 +120,148 @@ Then there are a few specific features that are only available in instrumentatio
NGRAM-x - deeper previous location coverage (from NGRAM-2 up to NGRAM-16)
In CLASSIC (default) and CFG/INSTRIM you can also specify CTX and/or
NGRAM, seperate the options with a comma "," then, e.g.:
AFL_LLVM_INSTRUMENT=CFG,CTX,NGRAM-4
`AFL_LLVM_INSTRUMENT=CFG,CTX,NGRAM-4`
Not that this is a good idea to use both CTX and NGRAM :)
### LTO
This is a different kind way of instrumentation: first it compiles all
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.
- AFL_LLVM_INSTRUMENT=CFG will use Control Flow Graph instrumentation.
- `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.)
None of the following options are necessary to be used and are rather for
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 seperated instrumentation are performed which
These are used if several separated instrumentations are performed which
are then later combined.
- AFL_LLVM_DOCUMENT_IDS=file will document to a file which edge ID was given
- `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
- `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.
- `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
- `AFL_LLVM_LTO_DONTWRITEID` prevents that the highest location ID written
into the instrumentation is set in a global variable
See instrumentation/README.LTO.md for more information.
See [instrumentation/README.lto.md](../instrumentation/README.lto.md) for more information.
### INSTRIM
This feature increases the speed by ~15% without any disadvantages to the
This feature increases the speed by ~15% without any disadvantages to the
classic instrumentation.
Note that there is also an LTO version (if you have llvm 11 or higher) -
Note that there is also an LTO version (if you have llvm 11 or higher) -
that is the best instrumentation we have. Use `afl-clang-lto` to activate.
The InsTrim LTO version additionally has all the options and features of
LTO (see above).
- Setting AFL_LLVM_INSTRIM or AFL_LLVM_INSTRUMENT=CFG to activates this mode
- Setting `AFL_LLVM_INSTRIM` or `AFL_LLVM_INSTRUMENT=CFG` activates this mode
- Setting AFL_LLVM_INSTRIM_LOOPHEAD=1 expands on INSTRIM to optimize loops.
- Setting `AFL_LLVM_INSTRIM_LOOPHEAD=1` expands on INSTRIM to optimize loops.
afl-fuzz will only be able to see the path the loop took, but not how
many times it was called (unless it is a complex loop).
See instrumentation/README.instrim.md
See [instrumentation/README.instrim.md](../instrumentation/README.instrim.md)
### NGRAM
- Setting AFL_LLVM_NGRAM_SIZE or AFL_LLVM_INSTRUMENT=NGRAM-{value}
- 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
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.ctx.md
See [instrumentation/README.ngram.md](../instrumentation/README.ngram.md)
### CTX
- Setting AFL_LLVM_CTX or AFL_LLVM_INSTRUMENT=CTX
- 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
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
See [instrumentation/README.ctx.md](../instrumentation/README.ctx.md)
### LAF-INTEL
This great feature will split compares to series of single byte comparisons
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_TRANSFORM_COMPARES will split string compare functions
- Setting `AFL_LLVM_LAF_TRANSFORM_COMPARES` will split string compare functions
- Setting AFL_LLVM_LAF_SPLIT_SWITCHES will split switch()es
- Setting `AFL_LLVM_LAF_SPLIT_SWITCHES` will split all `switch` constructs
- Setting AFL_LLVM_LAF_SPLIT_COMPARES will split all floating point and
- 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
- 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_ALL` sets all of the above
See instrumentation/README.laf-intel.md for more information.
See [instrumentation/README.laf-intel.md](../instrumentation/README.laf-intel.md) for more information.
### INSTRUMENT LIST (selectively instrument files and functions)
This feature allows selectively instrumentation of the source
This feature allows selective instrumentation of the source
- Setting AFL_LLVM_ALLOWLIST or AFL_LLVM_DENYLIST with a filenames and/or
- 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.
See instrumentation/README.instrument_list.md for more information.
See [instrumentation/README.instrument_list.md](../instrumentation/README.instrument_list.md) for more information.
### NOT_ZERO
- Setting AFL_LLVM_NOT_ZERO=1 during compilation will use counters
- 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.
- Setting AFL_LLVM_SKIP_NEVERZERO=1 will not implement the skip zero
- 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.
See instrumentation/README.neverzero.md
See [instrumentation/README.neverzero.md](../instrumentation/README.neverzero.md)
### CMPLOG
- Setting AFL_LLVM_CMPLOG=1 during compilation will tell afl-clang-fast to
produce a CmpLog binary. See instrumentation/README.cmplog.md
- Setting `AFL_LLVM_CMPLOG=1` during compilation will tell afl-clang-fast to
produce a CmpLog binary.
See instrumentation/README.neverzero.md
See [instrumentation/README.cmplog.md](../instrumentation/README.cmplog.md)
## 3) Settings for GCC / GCC_PLUGIN modes
Then there are a few specific features that are only available in GCC and
GCC_PLUGIN mode.
- Setting AFL_KEEP_ASSEMBLY prevents afl-as from deleting instrumented
- 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
```
- 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 gcc_plugin/README.instrument_list.md for more information.
See [instrumentation/README.instrument_list.md](../instrumentation/README.instrument_list.md) for more information.
(GCC_PLUGIN mode only)
## 4) Settings for afl-fuzz
@ -268,127 +269,127 @@ GCC_PLUGIN mode.
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
- 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.
- AFL_EXIT_WHEN_DONE causes afl-fuzz to terminate when all existing paths
- `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.
- AFL_MAP_SIZE sets the size of the shared map that afl-fuzz, afl-showmap,
- `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.
- AFL_TESTCACHE_SIZE allows you to overrider the define in config.h for
TESTCASE_CACHE. Recommended values are 50-250MB - or more if your
fuzzing finds a huge amount of paths for large inputs.
- `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_DISABLE_TRIM tells afl-fuzz to no trim test cases. This is
- 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
- 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_SKIP_CRASHES causes AFL to tolerate crashing files in the input
- `AFL_SKIP_CRASHES` causes AFL++ to tolerate crashing files in the input
queue. This can help with rare situations where a program crashes only
intermittently, but it's not really recommended under normal operating
conditions.
- Setting AFL_HANG_TMOUT allows you to specify a different timeout for
- 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
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
don't want AFL++ to spend too much time classifying that stuff and just
rapidly put all timeouts in that bin.
- AFL_NO_ARITH causes AFL to skip most of the deterministic arithmetics.
- `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.
- AFL_NO_SNAPSHOT will advice afl-fuzz not to use the snapshot feature
- `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
- `AFL_SHUFFLE_QUEUE` randomly reorders the input queue on startup. Requested
by some users for unorthodox parallelized fuzzing setups, but not
advisable otherwise.
- AFL_TMPDIR is used to write the .cur_input file to if exists, and in
- `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.
- 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
`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.
- When running in the -M or -S mode, setting AFL_IMPORT_FIRST causes the
- 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.
- Note that AFL_POST_LIBRARY is deprecated, use AFL_CUSTOM_MUTATOR_LIBRARY
- Note that `AFL_POST_LIBRARY` is deprecated, use `AFL_CUSTOM_MUTATOR_LIBRARY`
instead (see below).
- Setting AFL_CUSTOM_MUTATOR_LIBRARY to a shared library 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 builing
afl-fuzz), setting AFL_PYTHON_MODULE to a Python module can also provide
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
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_FAST_CAL keeps the calibration stage about 2.5x faster (albeit less
- `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.
- 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.
counts. To avoid the alarming red color, you can set `AFL_NO_CPU_RED`.
- In QEMU mode (-Q), AFL_PATH will be searched for afl-qemu-trace.
- In QEMU mode (-Q), `AFL_PATH` will be searched for afl-qemu-trace.
- Setting AFL_CYCLE_SCHEDULES will switch to a different schedule everytime
- 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
- 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_PRELOAD causes AFL to set LD_PRELOAD for the target binary
- 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_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_FORCE_UI will force painting the UI on the screen even if
- Setting `AFL_FORCE_UI` will force painting the UI on the screen even if
no valid terminal was detected (for virtual consoles)
- If you are Jakub, you may need AFL_I_DONT_CARE_ABOUT_MISSING_CRASHES.
- If you are Jakub, you may need `AFL_I_DONT_CARE_ABOUT_MISSING_CRASHES`.
Others need not apply.
- 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
- 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_OUTPUT will not suppress the child output.
- Setting `AFL_DEBUG_CHILD_OUTPUT` will not suppress the child output.
Not pretty but good for debugging purposes.
- Setting AFL_NO_CPU_RED will not display very high cpu usages in red color.
- Setting `AFL_NO_CPU_RED` will not display very high cpu usages in red color.
- Setting AFL_AUTORESUME will resume a fuzz run (same as providing `-i -`)
- 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.
- Setting AFL_NO_FORKSRV disables the forkserver optimization, reverting to
- 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).
@ -397,128 +398,128 @@ checks or alter some of the more exotic semantics of the tool:
normally done when starting up the forkserver and causes a pretty
significant performance drop.
- Setting AFL_STATSD enable 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
- Setting `AFL_STATSD` enable 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 get the most out of this, you should provide AFL_STATSD_TAGS_FLAVOR that
To get the most out of this, you should provide `AFL_STATSD_TAGS_FLAVOR` that
matches your StatsD server.
Available flavors are `dogstatsd`, `librato`, `signalfx` and `influxdb`.
- Outdated environment variables that are that not supported anymore:
AFL_DEFER_FORKSRV
AFL_PERSISTENT
- Outdated environment variables that are not supported anymore:
`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
- 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
- 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
- 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.
memcmp, ...) when libcompcov is preloaded using `AFL_PRELOAD`.
More info at qemu_mode/libcompcov/README.md.
There are two levels at the moment, AFL_COMPCOV_LEVEL=1 that instruments
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
`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
- 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
This is an alias of `AFL_COMPCOV_LEVEL=1` when `AFL_COMPCOV_LEVEL` is
not specified.
- The underlying QEMU binary will recognize any standard "user space
emulation" variables (e.g., QEMU_STACK_SIZE), but there should be no
emulation" variables (e.g., `QEMU_STACK_SIZE`), but there should be no
reason to touch them.
- AFL_DEBUG will print the found entrypoint for the binary to stderr.
- `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
use it directly, e.g. `afl-qemu-trace ./program`
- AFL_ENTRYPOINT allows you to specify a specific entrypoint into the
- `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
The entrypoint is specified as hex address, e.g. `0x4004110`
Note that the address must be the address of a basic block.
- 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`.
`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.
`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`.
- AFL_QEMU_PERSISTENT_GPR=1 QEMU will save the original value of general
- `AFL_QEMU_PERSISTENT_GPR=1` QEMU will save the original value of general
purpose registers and restore them in each persistent cycle.
- With AFL_QEMU_PERSISTENT_RETADDR_OFFSET you can specify the offset from the
- 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
hitted.
hit.
## 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).
- Setting `AFL_PATH` offers a way to specify the location of afl-showmap
and afl-qemu-trace (the latter only in `-Q` mode).
- AFL_KEEP_TRACES makes the tool keep traces and other metadata used for
- `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/*.
`<out_dir>/.traces/` directory.
- AFL_ALLOW_TMP permits this and some other scripts to run in /tmp. This is
- `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.
# #6) Settings for afl-tmin
Virtually nothing to play with. Well, in QEMU mode (-Q), AFL_PATH will be
searched for afl-qemu-trace. In addition to this, TMPDIR may be used if a
Virtually nothing to play with. Well, in QEMU mode (`-Q`), `AFL_PATH` will be
searched for afl-qemu-trace. In addition to this, `TMPDIR` may be used if a
temporary file can't be created in the current working directory.
You can specify AFL_TMIN_EXACT if you want afl-tmin to require execution paths
You can specify `AFL_TMIN_EXACT` if you want afl-tmin to require execution paths
to match when minimizing crashes. This will make minimization less useful, but
may prevent the tool from "jumping" from one crashing condition to another in
very buggy software. You probably want to combine it with the -e flag.
very buggy software. You probably want to combine it with the `-e` flag.
## 8) Settings for afl-analyze
You can set AFL_ANALYZE_HEX to get file offsets printed as hexadecimal instead
You can set `AFL_ANALYZE_HEX` to get file offsets printed as hexadecimal instead
of decimal.
## 9) Settings for libdislocator
The library honors these environmental variables:
- AFL_LD_LIMIT_MB caps the size of the maximum heap usage permitted by the
- `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_HARD_FAIL alters the behavior by calling abort() on excessive
allocations, thus causing what AFL would perceive as a crash. Useful for
- `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
- `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_NO_CALLOC_OVER inhibits abort() on calloc() overflows. Most
- `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_ALIGNED_ALLOC=1` will force the alignment of the allocation size to
`max_align_t` to be compliant with the C standard.
## 10) Settings for libtokencap
This library accepts AFL_TOKEN_FILE to indicate the location to which the
This library accepts `AFL_TOKEN_FILE` to indicate the location to which the
discovered tokens should be written.
## 11) Third-party variables set by afl-fuzz & other tools
@ -526,33 +527,33 @@ 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
- 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
override this by setting `LD_BIND_LAZY` beforehand, but it is almost
certainly pointless.
- By default, ASAN_OPTIONS are set to:
- By default, `ASAN_OPTIONS` are set to:
```
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 -
```
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
app. Similarly, include `symbolize=0`, since without it, AFL++ may have
difficulty telling crashes and hangs apart.
- In the same vein, by default, MSAN_OPTIONS are set to:
- 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
Be sure to include the first one when customizing anything, since some
MSAN versions don't call abort() on error, and we need a way to detect
```
Be sure to include the first one when customizing anything, since some
MSAN versions don't call `abort()` on error, and we need a way to detect
faults.