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| author | David Carlier <devnexen@gmail.com> | 2019-10-31 15:50:58 +0000 |
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| committer | David Carlier <devnexen@gmail.com> | 2019-10-31 15:50:58 +0000 |
| commit | b33bb0943ac4957eaf7b16ef694a4e4b4a538212 (patch) | |
| tree | 0bc1d9cf04b23fa8ecb73dd012dbc6db9ef72d17 /libtokencap/README.md | |
| parent | b17afc10a23cf87b3a0b8290491de4edd80c9c71 (diff) | |
| download | afl++-b33bb0943ac4957eaf7b16ef694a4e4b4a538212.tar.gz | |
libtokencap/libdislocator README rename proposals
and fixing the install tasks in the process.
Diffstat (limited to 'libtokencap/README.md')
| -rw-r--r-- | libtokencap/README.md | 64 |
1 files changed, 0 insertions, 64 deletions
diff --git a/libtokencap/README.md b/libtokencap/README.md deleted file mode 100644 index 8aae38bf..00000000 --- a/libtokencap/README.md +++ /dev/null @@ -1,64 +0,0 @@ -# strcmp() / memcmp() token capture library - - (See ../docs/README for the general instruction manual.) - -This 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. - -Portability hints: 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. - -Current supported OSes are: Linux, Darwin, FreeBSD (thanks to @devnexen) - |
