From b33bb0943ac4957eaf7b16ef694a4e4b4a538212 Mon Sep 17 00:00:00 2001 From: David Carlier Date: Thu, 31 Oct 2019 15:50:58 +0000 Subject: libtokencap/libdislocator README rename proposals and fixing the install tasks in the process. --- libtokencap/Makefile | 2 +- libtokencap/README.md | 64 ------------------------------------------ libtokencap/README.tokencap.md | 64 ++++++++++++++++++++++++++++++++++++++++++ libtokencap/libtokencap.so.c | 2 +- 4 files changed, 66 insertions(+), 66 deletions(-) delete mode 100644 libtokencap/README.md create mode 100644 libtokencap/README.tokencap.md (limited to 'libtokencap') diff --git a/libtokencap/Makefile b/libtokencap/Makefile index df2426ed..6e1319d8 100644 --- a/libtokencap/Makefile +++ b/libtokencap/Makefile @@ -49,5 +49,5 @@ clean: install: all install -m 755 ../libtokencap.so $${DESTDIR}$(HELPER_PATH) - install -m 644 README.tokencap $${DESTDIR}$(HELPER_PATH) + install -m 644 README.tokencap.md $${DESTDIR}$(HELPER_PATH) 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 /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) - diff --git a/libtokencap/README.tokencap.md b/libtokencap/README.tokencap.md new file mode 100644 index 00000000..8aae38bf --- /dev/null +++ b/libtokencap/README.tokencap.md @@ -0,0 +1,64 @@ +# 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 /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) + diff --git a/libtokencap/libtokencap.so.c b/libtokencap/libtokencap.so.c index 2fe9ae63..7495180d 100644 --- a/libtokencap/libtokencap.so.c +++ b/libtokencap/libtokencap.so.c @@ -15,7 +15,7 @@ This Linux-only companion library allows you to instrument strcmp(), memcmp(), and related functions to automatically extract tokens. - See README.tokencap for more info. + See README.tokencap.md for more info. */ -- cgit 1.4.1