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authorAndrea Fioraldi <andreafioraldi@gmail.com>2019-08-31 11:23:48 +0200
committerAndrea Fioraldi <andreafioraldi@gmail.com>2019-08-31 11:23:48 +0200
commit500a378fdf8664aea42f557f60c9842bb15f06a0 (patch)
tree76fd49c79a999e8112a148424eff4e177353fc7a /libtokencap/README.tokencap
parenteadd378f6c54a7e021985bca041d9642fff41034 (diff)
downloadafl++-500a378fdf8664aea42f557f60c9842bb15f06a0.tar.gz
modernize some readmes
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-=========================================
-strcmp() / memcmp() token capture library
-=========================================
-
-  (See ../docs/README for the general instruction manual.)
-
-This Linux-only companion library allows you to instrument strcmp(), memcmp(),
-and related functions to automatically extract syntax tokens passed to any of
-these libcalls. The resulting list of tokens may be then given as a starting
-dictionary to afl-fuzz (the -x option) to improve coverage on subsequent
-fuzzing runs.
-
-This may help improving coverage in some targets, and do precisely nothing in
-others. In some cases, it may even make things worse: if libtokencap picks up
-syntax tokens that are not used to process the input data, but that are a part
-of - say - parsing a config file... well, you're going to end up wasting a lot
-of CPU time on trying them out in the input stream. In other words, use this
-feature with care. Manually screening the resulting dictionary is almost
-always a necessity.
-
-As for the actual operation: the library stores tokens, without any deduping,
-by appending them to a file specified via AFL_TOKEN_FILE. If the variable is not
-set, the tool uses stderr (which is probably not what you want).
-
-Similarly to afl-tmin, the library is not "proprietary" and can be used with
-other fuzzers or testing tools without the need for any code tweaks. It does not
-require AFL-instrumented binaries to work.
-
-To use the library, you *need* to make sure that your fuzzing target is compiled
-with -fno-builtin and is linked dynamically. If you wish to automate the first
-part without mucking with CFLAGS in Makefiles, you can set AFL_NO_BUILTIN=1
-when using afl-gcc. This setting specifically adds the following flags:
-
-  -fno-builtin-strcmp -fno-builtin-strncmp -fno-builtin-strcasecmp
-  -fno-builtin-strcasencmp -fno-builtin-memcmp -fno-builtin-strstr
-  -fno-builtin-strcasestr
-
-The next step is simply loading this library via LD_PRELOAD. The optimal usage
-pattern is to allow afl-fuzz to fuzz normally for a while and build up a corpus,
-and then fire off the target binary, with libtokencap.so loaded, on every file
-found by AFL in that earlier run. This demonstrates the basic principle:
-
-  export AFL_TOKEN_FILE=$PWD/temp_output.txt
-
-  for i in <out_dir>/queue/id*; do
-    LD_PRELOAD=/path/to/libtokencap.so \
-      /path/to/target/program [...params, including $i...]
-  done
-
-  sort -u temp_output.txt >afl_dictionary.txt
-
-If you don't get any results, the target library is probably not using strcmp()
-and memcmp() to parse input; or you haven't compiled it with -fno-builtin; or
-the whole thing isn't dynamically linked, and LD_PRELOAD is having no effect.
-
-PS. The library is Linux-only because there is probably no particularly portable
-and non-invasive way to distinguish between read-only and read-write memory
-mappings. The __tokencap_load_mappings() function is the only thing that would
-need to be changed for other OSes. Porting to platforms with /proc/<pid>/maps
-(e.g., FreeBSD) should be trivial.
-