These are the instructions on how to fuzz the x86-64 kernel in a QEMU with Ubuntu 14.04 on the host machine and Debian Stretch in the QEMU instances.
Since syzkaller requires coverage support in GCC, we need to use a recent GCC version. To checkout GCC 7.1.0 sources to $GCC dir:
svn checkout svn://gcc.gnu.org/svn/gcc/trunk $GCC cd $GCC svn ls -v ^/tags | grep gcc_7_1_0_release svn up -r 247494
Unfortunately there's a typo in the source of gcc_7_1_0_release. Apply this fix:
diff --git a/gcc/tree.h b/gcc/tree.h index 3bca90a..fdaa7af 100644 --- a/gcc/tree.h +++ b/gcc/tree.h @@ -897,8 +897,8 @@ extern void omp_clause_range_check_failed (const_tree, const char *, int, /* If this is true, we should insert a __cilk_detach call just before this function call. */ #define EXPR_CILK_SPAWN(NODE) \ - (tree_check2 (NODE, __FILE__, __LINE__, __FUNCTION__, \ - CALL_EXPR, AGGR_INIT_EXPR)->base.u.bits.unsigned_flag) + (TREE_CHECK2 (NODE, CALL_EXPR, \ + AGGR_INIT_EXPR)->base.u.bits.unsigned_flag) /* In a RESULT_DECL, PARM_DECL and VAR_DECL, means that it is passed by invisible reference (and the TREE_TYPE is a pointer to the true
Install GCC prerequisites:
sudo apt-get install flex bison libc6-dev libc6-dev-i386 linux-libc-dev linux-libc-dev:i386 libgmp3-dev libmpfr-dev libmpc-dev build-essential bc
Build GCC:
mkdir build mkdir install cd build/ ../configure --enable-languages=c,c++ --disable-bootstrap --enable-checking=no --with-gnu-as --with-gnu-ld --with-ld=/usr/bin/ld.bfd --disable-multilib --prefix=$GCC/install/ make -j64 make install
Now you should have GCC binaries in $GCC/install/bin/:
$ ls $GCC/install/bin/ c++ gcc-ar gcov-tool x86_64-pc-linux-gnu-gcc-7.0.0 cpp gcc-nm x86_64-pc-linux-gnu-c++ x86_64-pc-linux-gnu-gcc-ar g++ gcc-ranlib x86_64-pc-linux-gnu-g++ x86_64-pc-linux-gnu-gcc-nm gcc gcov x86_64-pc-linux-gnu-gcc x86_64-pc-linux-gnu-gcc-ranlib
Checkout Linux kernel source:
git clone https://github.com/torvalds/linux.git $KERNEL
Generate default configs:
cd $KERNEL
make defconfig
make kvmconfig
Now we need to enable some config options required for syzkaller. Edit .config file manually and enable:
CONFIG_KCOV=y CONFIG_DEBUG_INFO=y CONFIG_KASAN=y CONFIG_KASAN_INLINE=y
You may also need the following for a recent linux image:
CONFIG_CONFIGFS_FS=y CONFIG_SECURITYFS=y
You might also want to enable some other kernel configs as described here.
Since enabling these options results in more sub options being available, we need to regenerate config. Run this and press enter each time when prompted for some config value to leave it as default:
make oldconfig
Build the kernel with previously built GCC:
make CC="$GCC/install/bin/gcc" -j64
Now you should have vmlinux (kernel binary) and bzImage (packed kernel image):
$ ls $KERNEL/vmlinux $KERNEL/vmlinux $ ls $KERNEL/arch/x86/boot/bzImage $KERNEL/arch/x86/boot/bzImage
Install debootstrap:
sudo apt-get install debootstrap
Create a Debian-stretch Linux image:
cd $IMAGE/ wget https://raw.githubusercontent.com/google/syzkaller/master/tools/create-image.sh -O create-image.sh chmod +x create-image.sh ./create-image.sh
By default, this script will create a minimal Debian-stretch Linux image. The result should be $IMAGE/stretch.img disk image.
If you would like to generate wheezy debian image, instead of stretch, just add one option of the script
./create-image.sh --distribution wheezy
Sometimes it's useful to have some additional packages and tools available in the VM even though they are not required to run syzkaller. The instructions to install some useful tools are below.
To install other packages, like make sysbench git vim tmux usbutils (not required to run syzkaller):
./create-image.sh --feature full
To install perf (not required to run syzkaller):
./create-image.sh --add-perf
Note: remember to set $KERNEL before installing perf
For additional options of create-image.sh, please refer to ./create-image.sh -h
Install QEMU:
sudo apt-get install qemu-system-x86
Make sure the kernel boots and sshd starts:
qemu-system-x86_64 \ -kernel $KERNEL/arch/x86/boot/bzImage \ -append "console=ttyS0 root=/dev/sda debug earlyprintk=serial slub_debug=QUZ"\ -hda $IMAGE/stretch.img \ -net user,hostfwd=tcp::10021-:22 -net nic \ -enable-kvm \ -nographic \ -m 2G \ -smp 2 \ -pidfile vm.pid \ 2>&1 | tee vm.log
early console in setup code early console in extract_kernel input_data: 0x0000000005d9e276 input_len: 0x0000000001da5af3 output: 0x0000000001000000 output_len: 0x00000000058799f8 kernel_total_size: 0x0000000006b63000 Decompressing Linux... Parsing ELF... done. Booting the kernel. [ 0.000000] Linux version 4.12.0-rc3+ ... [ 0.000000] Command line: console=ttyS0 root=/dev/sda debug earlyprintk=serial ... [ ok ] Starting enhanced syslogd: rsyslogd. [ ok ] Starting periodic command scheduler: cron. [ ok ] Starting OpenBSD Secure Shell server: sshd.
After that you should be able to ssh to QEMU instance in another terminal:
ssh -i $IMAGE/stretch.id_rsa -p 10021 -o "StrictHostKeyChecking no" root@localhost
If this fails with “too many tries”, ssh may be passing default keys before the one explicitly passed with -i. Append option -o "IdentitiesOnly yes".
To kill the running QEMU instance:
kill $(cat vm.pid)
Create a manager config like the following, replacing the environment variables $GOPATH, $KERNEL and $IMAGE with their actual values.
{
"target": "linux/amd64",
"http": "127.0.0.1:56741",
"workdir": "$GOPATH/src/github.com/google/syzkaller/workdir",
"kernel_obj": "$KERNEL",
"image": "$IMAGE/stretch.img",
"sshkey": "$IMAGE/stretch.id_rsa",
"syzkaller": "$GOPATH/src/github.com/google/syzkaller",
"procs": 8,
"type": "qemu",
"vm": {
"count": 4,
"kernel": "$KERNEL/arch/x86/boot/bzImage",
"cpu": 2,
"mem": 2048
}
}
Run syzkaller manager:
mkdir workdir ./bin/syz-manager -config=my.cfg
Now syzkaller should be running, you can check manager status with your web browser at 127.0.0.1:56741.
If you get issues after syz-manager starts, consider running it with the -debug flag. Also see this page for troubleshooting tips.