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| author | Andrea Fioraldi <andreafioraldi@gmail.com> | 2019-08-31 11:23:48 +0200 |
|---|---|---|
| committer | Andrea Fioraldi <andreafioraldi@gmail.com> | 2019-08-31 11:23:48 +0200 |
| commit | 500a378fdf8664aea42f557f60c9842bb15f06a0 (patch) | |
| tree | 76fd49c79a999e8112a148424eff4e177353fc7a /libtokencap/README.tokencap | |
| parent | eadd378f6c54a7e021985bca041d9642fff41034 (diff) | |
| download | afl++-500a378fdf8664aea42f557f60c9842bb15f06a0.tar.gz | |
modernize some readmes
Diffstat (limited to 'libtokencap/README.tokencap')
| -rw-r--r-- | libtokencap/README.tokencap | 61 |
1 files changed, 0 insertions, 61 deletions
diff --git a/libtokencap/README.tokencap b/libtokencap/README.tokencap deleted file mode 100644 index 650739f2..00000000 --- a/libtokencap/README.tokencap +++ /dev/null @@ -1,61 +0,0 @@ -========================================= -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. - |
