kAFL: Hardware-Assisted Feedback Fuzzing for OS Kernels

Blazing fast x86-64 VM kernel fuzzing framework with performant VM reloads for Linux, MacOS and Windows.

Published at USENIX Security 2017.

Currently missing:

• full documentation
• agents for macOS and Windows (except for our test driver)

BibTex:

@inproceedings{schumilo2017kafl,
    author = {Schumilo, Sergej and Aschermann, Cornelius and Gawlik, Robert and Schinzel, Sebastian and Holz, Thorsten},
    title = {{kAFL: Hardware-Assisted Feedback Fuzzing for OS Kernels}},
    year = {2017},
    booktitle = {USENIX Security Symposium} 
}

Trophies

• Linux keyctl null pointer dereference (CVE-2016-8650)
• Linux EXT4 memory corruption
• Linux EXT4 denial of service
• macOS APFS memory corruption (CVE-2017-13800)
• macOS HFS memory corruption (CVE-2017-13830)

Setup

This is a short introduction on how to setup kAFL to fuzz Linux kernel components.

Download kAFL and install necessary components

$ git clone https://github.com/RUB-SysSec/kAFL.git
$ cd kAFL
$ chmod u+x install.sh
$ sudo ./install.sh
$ sudo reboot

Setup VM

• Create QEMU hard drive image:

$ qemu-img create -f qcow2 linux.qcow2 20G

• Retrieve an ISO file of the desired OS and install it inside a VM (in this case Ubuntu 16.04 server):

$ wget -O /path/to/where/to/store/ubuntu.iso http://de.releases.ubuntu.com/16.04/ubuntu-16.04.3-server-amd64.iso
$ qemu-system-x86_64 -cpu host -enable-kvm -m 512 -hda linux.qcow2 -cdrom ubuntu.iso -usbdevice tablet

• Download kAFL and compile the loader agent:

git clone https://github.com/RUB-SysSec/kAFL.git
cd path/to/kAFL/kAFL-Fuzzer/agents
chmod u+x compile.sh
./compile.sh

• Shutdown the VM

Prepare VM for kAFL fuzzing

• On the host: Create Overlay and Snapshot Files:

mkdir snapshot && cd snapshot
qemu-img create -b /absolute/path/to/hdd/linux.qcow2 -f qcow2 overlay_0.qcow2
qemu-img create -f qcow2 ram.qcow2 512

• Start the VM using QEMU-PT:

cd /path/to/kAFL
./qemu-2.9.0/x86_64-softmmu/qemu-system-x86_64 -hdb /path/to/snapshot/ram.qcow2 -hda /path/to/snapshot/overlay_0.qcow2 -machine pc-i440fx-2.6 -serial mon:stdio -enable-kvm -k de -m 512

• (Optional) Install and load the vulnerable Test Driver:

cd path/to/kAFl/kAFL-Fuzzer/vuln_drivers/simple/linux_x86-64/
chmod u+x load.sh
sudo ./load.sh

• Execute loader binary which is in path/to/kAFL/kAFL-Fuzzer/agents/linux_x86_64/loader/ as root. VM should freeze. Switch to the QEMU management console and create a snapshot:

# press CTRL-a + c
savevm kafl
q 

Compile and configure kAFL components

• Edit /path/to/kAFL/kAFL-Fuzzer/kafl.ini (qemu-kafl_location to point to path/to/kAFL/qemu-2.9.0/x86_64-softmmu/qemu-system-x86_64)

• Compile agents:

cd <KERNEL_AFL_ROOT>/kAFL-Fuzzer/agents
chmod u+x compile.sh
./compile.sh

• Retrieve address ranges of loaded drivers:

cd /path/to/kAFL/kAFL-Fuzzer
python kafl_info.py /path/to/snapshot/ram.qcow2 /path/to/snapshot/ agents/linux_x86_64/info/info 512 -v

Start Fuzzing!

python kafl_fuzz.py /path/to/snapshot/ram.qcow2 /path/to/snapshot agents/linux_x86_64/fuzzer/kafl_vuln_test 512 /path/to/input/directory /path/to/working/directory -ip0 0xffffffffc0287000-0xffffffffc028b000 -v --Purge

The value ip0 is the address range of the fuzzing target.