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setup_linux-host_qemu-vm_s390x-kernel.md

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Setup: Debian/Ubuntu/Fedora host, QEMU vm, s390x kernel

GCC

Obtain s390x-linux-gnu-gcc at least GCC version 9. The latest Debian/Ubuntu/Fedora distributions should provide a recent enough version of a cross-compiler in the gcc-s390x-linux-gnu package.

Kernel

Checkout Linux kernel source:

git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git $KERNEL

Generate default configs:

cd $KERNEL
make ARCH=s390 CROSS_COMPILE=s390x-linux-gnu- defconfig
make ARCH=s390 CROSS_COMPILE=s390x-linux-gnu- kvm_guest.config

Enable kernel config options required for syzkaller as described here.

./scripts/config --file .config \
                 -d MODULES \
                 -e KCOV \
                 -e KCOV_INSTRUMENT_ALL \
                 -e KCOV_ENABLE_COMPARISONS \
                 -e KASAN \
                 -e KASAN_INLINE \
                 -e CONFIGFS_FS \
                 -e SECURITYFS \
                 -e DEBUG_INFO \
                 -e GDB_SCRIPTS \
                 -e PRINTK \
                 -e EARLY_PRINTK \
                 -e DEVTMPFS \
                 -e TUN \
                 -e VIRTIO_PCI \
                 -e VIRTIO_NET \
                 -e NET_9P_VIRTIO \
                 -e NET_9P \
                 -e 9P_FS \
                 -e BINFMT_MISC \
                 -e FAULT_INJECTION \
                 -e FAILSLAB \
                 -e FAIL_PAGE_ALLOC \
                 -e FAIL_MAKE_REQUEST \
                 -e FAIL_IO_TIMEOUT \
                 -e FAIL_FUTEX \
                 -e FAULT_INJECTION_DEBUG_FS \
                 -e FAULT_INJECTION_STACKTRACE_FILTER \
                 -e DEBUG_KMEMLEAK

Edit .config file manually and enable them (or do that through make menuconfig if you prefer).

Since enabling these options results in more sub options being available, we need to regenerate config:

make ARCH=s390 CROSS_COMPILE=s390x-linux-gnu- olddefconfig

Build the kernel:

make ARCH=s390 CROSS_COMPILE=s390x-linux-gnu- -j$(nproc)

Now you should have vmlinux (kernel binary) and bzImage (packed kernel image):

$ ls $KERNEL/vmlinux
$KERNEL/vmlinux
$ ls $KERNEL/arch/s390/boot/bzImage
$KERNEL/arch/s390/boot/bzImage

Image

Debian

To create a Debian Linux image with the minimal set of required packages do:

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 -a s390x

The result should be $IMAGE/trixie.img disk image.

For additional options of create-image.sh, please refer to ./create-image.sh -h

QEMU

Debian

Run:

qemu-system-s390x \
	-M s390-ccw-virtio -cpu max,zpci=on -m 4G -smp 2 \
	-kernel $KERNEL/arch/s390/boot/bzImage \
	-drive file=$IMAGE/trixie.img,if=virtio,format=raw \
	-append "rootwait root=/dev/vda net.ifnames=0 biosdevname=0" \
	-net nic,model=virtio -net user,host=10.0.2.10,hostfwd=tcp:127.0.0.1:10021-:22 \
	-display none -serial mon:stdio \
	-pidfile vm.pid 2>&1 | tee vm.log

After that you should be able to ssh to QEMU instance in another terminal:

ssh -i $IMAGE/trixie.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 press Ctrl+A and then X or run:

kill $(cat vm.pid)

If QEMU works, the kernel boots and ssh succeeds, you can shutdown QEMU and try to run syzkaller.

syzkaller

Build syzkaller as described here, with s390x target:

make TARGETOS=linux TARGETARCH=s390x

Then create a manager config like the following, replacing the environment variables $GOPATH, $KERNEL and $IMAGE with their actual values.

{
	"target": "linux/s390x",
	"http": "127.0.0.1:56741",
	"workdir": "$GOPATH/src/github.com/google/syzkaller/workdir",
	"kernel_obj": "$KERNEL",
	"image": "$IMAGE/trixie.img",
	"sshkey": "$IMAGE/trixie.id_rsa",
	"syzkaller": "$GOPATH/src/github.com/google/syzkaller",
	"procs": 8,
	"type": "qemu",
	"vm": {
		"count": 4,
		"kernel": "$KERNEL/arch/s390/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.