#!/bin/bash
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# Copyright 2016 syzkaller project authors. All rights reserved.
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# Use of this source code is governed by Apache 2 LICENSE that can be found in the LICENSE file.
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# create-gce-image.sh creates a minimal bootable image suitable for syzkaller/GCE.
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# The image will have password-less root login with a key stored in key file.
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#
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# Prerequisites:
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# - you need a user-space system, a basic Debian system can be created with:
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# sudo debootstrap --include=openssh-server,curl,tar,gcc,libc6-dev,time,strace,sudo,less,psmisc,selinux-utils,policycoreutils,checkpolicy,selinux-policy-default stable debian
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# - you need kernel to use with image (e.g. arch/x86/boot/bzImage)
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# note: kernel modules are not supported
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# - you need grub:
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# sudo apt-get install grub-efi
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#
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# Usage:
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# ./create-gce-image.sh /dir/with/user/space/system /path/to/bzImage
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#
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# SYZ_VM_TYPE env var controls type of target test machine. Supported values:
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# - qemu (default, uses /dev/loop)
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# - gce (uses /dev/nbd0)
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# Needs nbd support in kernel and qemu-utils (qemu-nbd) installed.
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#
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# If SYZ_SYSCTL_FILE env var is set and points to a file,
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# then its contents will be appended to the image /etc/sysctl.conf.
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# If SYZ_CMDLINE_FILE env var is set and points to a file,
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# then its contents will be appended to the kernel command line.
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# If MKE2FS_CONFIG env var is set, it will affect invoked mkfs.ext4.
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#
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# Outputs are (in the current dir):
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# - disk.raw: the image
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# - key: root ssh key
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# The script can also create/delete temp files in the current dir.
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#
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# The image then needs to be compressed with:
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# tar -Sczf disk.tar.gz disk.raw
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# and uploaded to GCS with:
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# gsutil cp disk.tar.gz gs://my-images/image.tar.gz
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# finally, my-images/image.tar.gz can be used to create a new GCE image.
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#
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# The image can be tested locally with e.g.:
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# qemu-system-x86_64 -hda disk.raw -net user,host=10.0.2.10,hostfwd=tcp::10022-:22 \
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# -net nic -enable-kvm -m 2G -display none -serial stdio
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# once the kernel boots, you can ssh into it with:
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# ssh -o UserKnownHostsFile=/dev/null -o StrictHostKeyChecking=no -o IdentitiesOnly=yes \
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# -p 10022 -i key root@localhost
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set -eux
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CLEANUP=""
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trap 'eval " $CLEANUP"' EXIT
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if [ ! -e $1/sbin/init ]; then
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echo "usage: create-gce-image.sh /dir/with/user/space/system /path/to/bzImage"
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exit 1
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fi
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if [ "$(basename $2)" != "bzImage" ]; then
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echo "usage: create-gce-image.sh /dir/with/user/space/system /path/to/bzImage"
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exit 1
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fi
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SYZ_VM_TYPE="${SYZ_VM_TYPE:-qemu}"
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if [ "$SYZ_VM_TYPE" == "qemu" ]; then
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:
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elif [ "$SYZ_VM_TYPE" == "gce" ]; then
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:
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else
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echo "SYZ_VM_TYPE has unsupported value $SYZ_VM_TYPE"
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exit 1
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fi
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# Clean up after previous unsuccessful run.
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sudo umount disk.mnt || true
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if [ "$SYZ_VM_TYPE" == "qemu" ]; then
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:
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elif [ "$SYZ_VM_TYPE" == "gce" ]; then
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sudo modprobe nbd
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sudo qemu-nbd -d /dev/nbd0 || true
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fi
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rm -rf disk.mnt disk.raw || true
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fallocate -l 2G disk.raw
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if [ "$SYZ_VM_TYPE" == "qemu" ]; then
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DISKDEV="$(sudo losetup -f --show -P disk.raw)"
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CLEANUP="sudo losetup -d $DISKDEV; $CLEANUP"
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elif [ "$SYZ_VM_TYPE" == "gce" ]; then
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DISKDEV="/dev/nbd0"
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sudo qemu-nbd -c $DISKDEV --format=raw disk.raw
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CLEANUP="sudo qemu-nbd -d $DISKDEV; $CLEANUP"
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fi
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echo -en "o\nn\np\n1\n\n\na\nw\n" | sudo fdisk $DISKDEV
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PARTDEV=$DISKDEV"p1"
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until [ -e $PARTDEV ]; do sleep 1; done
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sudo -E mkfs.ext4 $PARTDEV
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mkdir -p disk.mnt
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CLEANUP="rm -rf disk.mnt; $CLEANUP"
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sudo mount $PARTDEV disk.mnt
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CLEANUP="sudo umount disk.mnt; $CLEANUP"
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sudo cp -a $1/. disk.mnt/.
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sudo cp $2 disk.mnt/vmlinuz
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sudo sed -i "/^root/ { s/:x:/::/ }" disk.mnt/etc/passwd
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echo "T0:23:respawn:/sbin/getty -L ttyS0 115200 vt100" | sudo tee -a disk.mnt/etc/inittab
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echo -en "auto lo\niface lo inet loopback\nauto eth0\niface eth0 inet dhcp\n" | sudo tee disk.mnt/etc/network/interfaces
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echo "debugfs /sys/kernel/debug debugfs defaults 0 0" | sudo tee -a disk.mnt/etc/fstab
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echo 'binfmt_misc /proc/sys/fs/binfmt_misc binfmt_misc defaults 0 0' | sudo tee -a disk.mnt/etc/fstab
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for i in {0..31}; do
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echo "KERNEL==\"binder$i\", NAME=\"binder$i\", MODE=\"0666\"" | \
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sudo tee -a disk.mnt/etc/udev/50-binder.rules
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done
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# We disable selinux for now because the default policy on wheezy prevents
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# mounting of cgroup2 (and stretch we don't know how to configure yet).
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echo 'SELINUX=disabled' | sudo tee disk.mnt/etc/selinux/config
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# sysctls
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echo "kernel.printk = 7 4 1 3" | sudo tee -a disk.mnt/etc/sysctl.conf
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echo "debug.exception-trace = 0" | sudo tee -a disk.mnt/etc/sysctl.conf
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SYZ_SYSCTL_FILE="${SYZ_SYSCTL_FILE:-}"
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if [ "$SYZ_SYSCTL_FILE" != "" ]; then
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cat $SYZ_SYSCTL_FILE | sudo tee -a disk.mnt/etc/sysctl.conf
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fi
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echo -en "127.0.0.1\tlocalhost\n" | sudo tee disk.mnt/etc/hosts
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echo "nameserver 8.8.8.8" | sudo tee -a disk.mnt/etc/resolve.conf
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echo "ClientAliveInterval 420" | sudo tee -a disk.mnt/etc/ssh/sshd_config
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echo "syzkaller" | sudo tee disk.mnt/etc/hostname
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rm -f key key.pub
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ssh-keygen -f key -t rsa -N ""
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sudo mkdir -p disk.mnt/root/.ssh
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sudo cp key.pub disk.mnt/root/.ssh/authorized_keys
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sudo chown root disk.mnt/root/.ssh/authorized_keys
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sudo mkdir -p disk.mnt/boot/grub
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CMDLINE=""
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SYZ_CMDLINE_FILE="${SYZ_CMDLINE_FILE:-}"
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if [ "$SYZ_CMDLINE_FILE" != "" ]; then
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CMDLINE=$(awk '{printf("%s ", $0)}' $SYZ_CMDLINE_FILE)
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fi
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cat << EOF | sudo tee disk.mnt/boot/grub/grub.cfg
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terminal_input console
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terminal_output console
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set timeout=0
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# vsyscall=native: required to run x86_64 executables on android kernels
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# (for some reason they disable VDSO by default)
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# rodata=n: mark_rodata_ro becomes very slow with KASAN (lots of PGDs)
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# panic=86400: prevents kernel from rebooting so that we don't get reboot output in all crash reports
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# debug is not set as it produces too much output
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menuentry 'linux' --class gnu-linux --class gnu --class os {
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insmod vbe
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insmod vga
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insmod video_bochs
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insmod video_cirrus
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insmod gzio
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insmod part_msdos
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insmod ext2
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set root='(hd0,1)'
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linux /vmlinuz root=/dev/sda1 console=ttyS0 earlyprintk=serial vsyscall=native rodata=n ftrace_dump_on_oops=orig_cpu oops=panic panic_on_warn=1 nmi_watchdog=panic panic=86400 $CMDLINE
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}
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EOF
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sudo grub-install --target=i386-pc --boot-directory=disk.mnt/boot --no-floppy $DISKDEV
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