Written and maintaned by Andrea Fioraldi [email protected]
For just usermode fuzzing, a more updated version of QASan is now embedded into AFL++, use it instead
QASan is a custom QEMU 3.1.1 that detects memory errors in the guest using AddressSanitizer.
As QEMU is a binary code emulator, QASan is a binary-only sanitizer and does not require compiler-based instrumentation.
Dowload it with:
git clone --recursive https://github.com/andreafioraldi/qasan.git
QASan comes in two possible twists, one based on my own ASan implementation and the other on the clang's implementation of ASan.
build.py is the script used to build all.
The flag --system allows you to build full-system QASan, an experimental feature ATM.
asan-giovese is my implementation of AddressSanitizer. It is in pure C11 and allows you to get useful informations from the target process like stacktraces on allocations and on errors.
It will be the only supported option in future, but at the moment is not already completely thread safe.
This is the default mode, built when you don't specify the --asan-dso flag.
You need the lief python3 package.
Build using the build.py script specifying the path to the ASan DSO.
./build.py --asan-dso /path/to/libclang_rt.asan-ARCH.so
On Ubuntu 18.04, the path is /usr/lib/llvm-8/lib/clang/8.0.0/lib/linux/libclang_rt.asan-x86_64.so
Note that QASan will not output meaningful stacktraces or error reports when using this mode.
The reported errors show informaton about the QEMU host and so they are not useful for debugging.
Other available build options are:
--archto specify the target architecture (default is x86_64)--ccand--cxxto specify C and C++ compilers (default clang-8)--crossto specify the cross C compiler for libqasan--cleanto clean builded files
Tested only on Ubuntu 18.04 with x86[_64] and arm[64] targets.
To simply run a binary under QASan:
./qasan ./program args...
To set the LD path (useful when running cross arch, in this case armhf):
./qasan --prefix /usr/arm-linux-gnueabihf/ ./program args...
Other options are --preload to preload a shared object, --verbose to get a verbose output with memory mappings and --debug to log hooked actions if libqasan is compiled in debug mode.
By default, only the main executable memory accesses are instrumented. To enable the instrumentation of all the libraries, use AFL_INST_LIBS=1.
Beware that glibc have a lot of assumptions on buffer size and a lot of handwritten magic (see this). If you have an error caused by these optimizations you can disable the instrumentation for single functions adding them to libqasan/uninstrument.c.
To fuzz a binary with QASan and AFL++ use a command similar to the following:
~/AFLplusplus/afl-fuzz -U -i in -o out -m none -- python3 ~/qasan/qasan ./program
It supports all the AFL++ QEMU configurations, AFL_COMPCOV_LEVEL=2 is higly suggested.
To improve speed, set the env variables QASAN_MAX_CALL_STACK=0 and QASAN_SYMBOLIZE=0.
When I should use QASan?
If your target binary is PIC x86_64, you should before give a try to retrowrite for static rewriting.
If it fails, or if your binary is for another architecture, QASan is the tool that you want/have to use.
Note that the overhead of AFL++ libdislocator is much lower but it can catch less bugs. This is a short blanket, take your choice.
Another discriminat for the choice is CompareCoverage. If your target has fuzzing roadblocks, you can use QASan+CompCov to fuzz it with Sanitization and Roadblocks bypassing.
QEMU segfaults with big endian archs
See https://bugs.launchpad.net/qemu/+bug/1701798, use the workaround described here.
Native (slowdown: 1x):
$ time /usr/bin/objdump -g -x /usr/bin/objdump
...
real 0m0,058s
user 0m0,010s
sys 0m0,029s
QEMU (slowdown: 2.4x):
$ time qemu-x86_64 /usr/bin/objdump -g -x /usr/bin/objdump
...
real 0m0,141s
user 0m0,096s
sys 0m0,020s
QASan (slowdown: 3.6x):
$ time ./qasan /usr/bin/objdump -g -x /usr/bin/objdump
...
real 0m0,209s
user 0m0,120s
sys 0m0,032s
Valgrind (slowdown: 17.4x):
$ time valgrind /usr/bin/objdump -g -x /usr/bin/objdump
...
real 0m1,009s
user 0m0,921s
sys 0m0,076s
If you use QASan for your academic work, you should cite the following pubblication:
- Andrea Fioraldi, Daniele Cono D’Elia, and Leonardo Querzoni. “Fuzzing binaries for memory safety errors with QASan”. In 2020 IEEE Secure Development Conference (SecDev), 2020.
Preprint: https://andreafioraldi.github.io/assets/qasan-secdev20.pdf
Bibtex:
@INPROCEEDINGS{QASan-SecDev20,
author={Fioraldi, Andrea and D’Elia, Daniele Cono and Querzoni, Leonardo},
title={Fuzzing Binaries for Memory Safety Errors with {QASan}},
booktitle={2020 IEEE Secure Development Conference (SecDev)},
doi={10.1109/SecDev45635.2020.00019},
pages={23--30},
year={2020}
}Video: https://www.youtube.com/watch?v=UtFXU7Nkd8g
Slides: https://andreafioraldi.github.io/assets/qasan-secdev20-slides.pdf