Crash because of user-defined exceptions when running thru the fuzzer

[googleprojectzero]

Crash because of user-defined exceptions when running thru the fuzzer

[ifratric]

Two points here

• If the target uses custom exceptions you need to also pass -patch_return_addresses as discussed in the TinyInst readme. An alternative (since -patch_return_addresses comes with a nonnegligible performance cost) is to use a 32-bit build of your target, as exception handing is done differently in 32- and 64-bit programs and 32-bit works out-of-the-box. Note that you don't need to rebuild Jackalope for 32-bit targets, a 64-bit fuzzer build should run fine against both 64- and 32-bit targets.

• If you want hangs to be saved, you need to flip the save_hangs flag here https://github.com/googleprojectzero/Jackalope/blob/main/fuzzer.cpp#L40. Note that you need to do it in the source, as currently it isn't exposed as the command line flag.

[rajeemm]

Thanks, it works perfectly (x86).
One question regarding hangs, though. Is it the default to not save hangs because it is less of an exploitable security issue (other than DoS)?

[ifratric]

Hangs are more difficult to deduplicate, so if your code produces a lot of hangs for whatever reasons, it would create a lot of files quickly. Additionally, as you said, hangs might not be as interesting from the security standpoint.

[rajeemm]

Great, thanks! (closing issue)