tools: add script for building of buildroot images

We used to use Debian-based images, but they have several issues:
1. They boot too slowly (we don't need full systemd power).
2. Systemd mounts cgroup controllers so that we can't use them during fuzzing
   (can be mounted only once).
3. We have poor control over contents of the image.

This script creates lightweight buildroot-based images that boot fast.

tools/create-buildroot-image.sh

@@ -0,0 +1,221 @@
+#!/usr/bin/env bash
+# Copyright 2021 syzkaller project authors. All rights reserved.
+# Use of this source code is governed by Apache 2 LICENSE that can be found in the LICENSE file.
+
+# This script builds a buildroot-based Linux image.
+# It should be run from a buildroot checkout (git://git.buildroot.net/buildroot) as:
+# TARGETARCH={amd64,arm64,arm,riscv64,s390x,mips64le,ppc64le} [NOMAKE=yes] create-buildroot-image.sh
+# If no NOMAKE=yes is specified, then it will just prepare the buildroot config,
+# but will not run the final make.
+# For amd64 it creates a bootable image with root partition
+# on /dev/sda1 in output/images/disk.img file.
+# For other architectures it creates a non-bootable disk
+# suitable qemu injected boot with root partition on /dev/sda
+# in output/images/rootfs.ext4 file.
+# Note: the image requires at least kernel v4.19
+# (otherwise glibc complains about unsupported kernel version).
+
+set -eux
+
+NOMAKE="${NOMAKE:-}"
+TARGETARCH="${TARGETARCH:-amd64}"
+case "$TARGETARCH" in
+ amd64)
+ DEFCONFIG="pc_x86_64_bios_defconfig";;
+ arm64)
+ DEFCONFIG="qemu_aarch64_virt_defconfig";;
+ arm)
+ DEFCONFIG="qemu_arm_vexpress_defconfig";;
+ riscv64)
+ DEFCONFIG="qemu_riscv64_virt_defconfig";;
+ s390x)
+ DEFCONFIG="qemu_s390x_defconfig";;
+ mips64le)
+ DEFCONFIG="qemu_mips64r6el_malta_defconfig";;
+ ppc64le)
+ DEFCONFIG="qemu_ppc64le_pseries_defconfig";;
+ *)
+ echo "unsupported TARGETARCH=${TARGETARCH}"
+ exit 1;;
+esac
+
+git fetch origin
+git checkout 2021.08.x
+
+make "${DEFCONFIG}"
+
+# Common configs for all architectures.
+cat >>.config <<EOF
+BR2_TARGET_GENERIC_HOSTNAME="syzkaller"
+BR2_TARGET_GENERIC_ISSUE="syzkaller"
+BR2_ROOTFS_POST_FAKEROOT_SCRIPT="./rootfs_script.sh"
+BR2_TOOLCHAIN_BUILDROOT_GLIBC=y
+BR2_PACKAGE_DHCPCD=y
+BR2_PACKAGE_OPENSSH=y
+
+# This slows down boot.
+# BR2_PACKAGE_URANDOM_SCRIPTS is not set
+
+BR2_TARGET_ROOTFS_EXT2_SIZE="1G"
+# Slightly more interesting and realistic options.
+BR2_TARGET_ROOTFS_EXT2_MKFS_OPTIONS="-O 64bit,ext_attr,encrypt,verity,extents,huge_file,flex_bg,dir_nlink,sparse_super,resize_inode,has_journal"
+
+# Install firmware for USB devices we can connect during fuzzing.
+BR2_PACKAGE_LINUX_FIRMWARE=y
+BR2_PACKAGE_LINUX_FIRMWARE_MEDIATEK_MT7650=y
+BR2_PACKAGE_LINUX_FIRMWARE_MEDIATEK_MT7601U=y
+BR2_PACKAGE_LINUX_FIRMWARE_MEDIATEK_MT7610E=y
+BR2_PACKAGE_LINUX_FIRMWARE_MEDIATEK_MT76X2E=y
+BR2_PACKAGE_LINUX_FIRMWARE_AR3012_USB=y
+BR2_PACKAGE_LINUX_FIRMWARE_BRCM_BCM43XX=y
+BR2_PACKAGE_LINUX_FIRMWARE_BRCM_BCM43XXX=y
+BR2_PACKAGE_LINUX_FIRMWARE_LIBERTAS_USB8388_V9=y
+BR2_PACKAGE_LINUX_FIRMWARE_LIBERTAS_USB8388_OLPC=y
+BR2_PACKAGE_LINUX_FIRMWARE_LIBERTAS_USB_THINFIRM=y
+BR2_PACKAGE_LINUX_FIRMWARE_MWIFIEX_USB8797=y
+BR2_PACKAGE_LINUX_FIRMWARE_MWIFIEX_USB8801=y
+BR2_PACKAGE_LINUX_FIRMWARE_MWIFIEX_USB8897=y
+BR2_PACKAGE_LINUX_FIRMWARE_RALINK_RT61=y
+BR2_PACKAGE_LINUX_FIRMWARE_RALINK_RT73=y
+BR2_PACKAGE_LINUX_FIRMWARE_RALINK_RT2XX=y
+BR2_PACKAGE_LINUX_FIRMWARE_AS102=y
+BR2_PACKAGE_LINUX_FIRMWARE_DIB0700=y
+BR2_PACKAGE_LINUX_FIRMWARE_ITETECH_IT9135=y
+BR2_PACKAGE_LINUX_FIRMWARE_CX231XX=y
+BR2_PACKAGE_LINUX_FIRMWARE_QUALCOMM_WIL6210=y
+# This one we could use, but it breaks buildroot:
+# Makefile.legacy:9: *** You have legacy configuration in your .config! Please check your configuration.
+# BR2_PACKAGE_LINUX_FIRMWARE_ATHEROS_10K_QCA6174=y
+BR2_PACKAGE_LINUX_FIRMWARE_ATHEROS_10K_QCA998X=y
+BR2_PACKAGE_LINUX_FIRMWARE_ATHEROS_10K_QCA9377=y
+BR2_PACKAGE_ZD1211_FIRMWARE=y
+
+# These packages seem to enable rfkill (and are unnecessary).
+# BR2_PACKAGE_CONNMAN is not set
+# BR2_PACKAGE_WPA_SUPPLICANT is not set
+
+# These packages enable SELinux policy.
+BR2_PACKAGE_LIBSELINUX=y
+BR2_PACKAGE_REFPOLICY=y
+BR2_PACKAGE_REFPOLICY_POLICY_STATE_PERMISSIVE=y
+# BR2_PACKAGE_REFPOLICY_POLICY_STATE_ENFORCING is not set
+# BR2_PACKAGE_REFPOLICY_POLICY_STATE_DISABLED is not set
+EOF
+
+# Per-arch config fragments.
+case "$TARGETARCH" in
+ amd64)
+ cat >>.config <<EOF
+BR2_TARGET_GENERIC_GETTY_PORT="ttyS0"
+BR2_LINUX_KERNEL_USE_ARCH_DEFAULT_CONFIG=y
+BR2_LINUX_KERNEL_CONFIG_FRAGMENT_FILES="board/qemu/x86_64/linux.config"
+# This is used to create some device links in devfs (see udev rules below),
+# but this is too slow for emulated architectures.
+BR2_ROOTFS_DEVICE_CREATION_DYNAMIC_EUDEV=y
+EOF
+;;
+ arm64)
+ cat >>.config <<EOF
+BR2_cortex_a57=y
+# Kernel is not needed for non-bootable images.
+# BR2_LINUX_KERNEL is not set
+EOF
+;;
+ arm)
+ cat >>.config <<EOF
+BR2_cortex_a57=y
+# BR2_LINUX_KERNEL is not set
+EOF
+;;
+ s390x)
+ cat >>.config <<EOF
+# BR2_LINUX_KERNEL is not set
+EOF
+;;
+ mips64le)
+ cat >>.config <<EOF
+# BR2_LINUX_KERNEL is not set
+EOF
+;;
+ ppc64le)
+ cat >>.config <<EOF
+# BR2_LINUX_KERNEL is not set
+EOF
+;;
+ riscv64)
+ cat >>.config <<EOF
+# BR2_LINUX_KERNEL is not set
+EOF
+;;
+esac
+
+# This script modifies the target root filesystem
+# before it's packed into the final image.
+# This part is common for all architectures.
+cat >rootfs_script.sh <<'EOFEOF'
+set -eux
+
+# Mount debugfs for KCOV and other filesystems.
+cat >>$1/etc/fstab <<EOF
+debugfs /sys/kernel/debug debugfs defaults 0 0
+securityfs /sys/kernel/security securityfs defaults 0 0
+configfs /sys/kernel/config/ configfs defaults 0 0
+binfmt_misc /proc/sys/fs/binfmt_misc binfmt_misc defaults 0 0
+smackfs /sys/fs/smackfs smackfs defaults 0 0
+selinuxfs /sys/fs/selinux selinuxfs defaults 0 0
+fusectl /sys/fs/fuse/connections fusectl defaults 0 0
+pstore /sys/fs/pstore pstore defaults 0 0
+bpf /sys/fs/bpf bpf defaults 0 0
+mqueue /dev/mqueue mqueue defaults 0 0
+hugetlbfs /dev/hugepages hugetlbfs defaults 0 0
+tracefs /sys/kernel/tracing tracefs defaults 0 0
+fuse.lxcfs /var/lib/lxcfs fuse.lxcfs defaults 0 0
+EOF
+
+# Setup ssh without key/password.
+cat >$1/etc/ssh/sshd_config <<EOF
+PermitRootLogin yes
+PasswordAuthentication yes
+PermitEmptyPasswords yes
+ClientAliveInterval 420
+EOF
+
+# Generate sshd host keys.
+ssh-keygen -A -f $1
+mkdir -p $1/var/db/dhcpcd
+
+EOFEOF
+
+# Per-arch part of the rootfs script.
+case "$TARGETARCH" in
+ amd64)
+cat >>rootfs_script.sh <<'EOFEOF'
+
+# Write udev rules.
+cat >$1/etc/udev/rules.d/50-syzkaller.rules <<EOF
+ATTR{name}=="vim2m", SYMLINK+="vim2m"
+SUBSYSTEMS=="pci", DRIVERS=="i915", SYMLINK+="i915"
+EOF
+for i in {0..31}; do
+ echo "KERNEL==\"binder$i\", NAME=\"binder$i\", MODE=\"0666\"" >> $1/etc/udev/rules.d/50-syzkaller.rules
+done
+
+# Override default grub config with timeout 0.
+cat >$1/boot/grub/grub.cfg <<EOF
+set default="0"
+set timeout="0"
+menuentry "syzkaller" {
+ linux /boot/bzImage root=/dev/sda1 console=ttyS0
+}
+EOF
+EOFEOF
+;;
+esac
+
+chmod u+x rootfs_script.sh
+
+make olddefconfig
+
+if [[ "$NOMAKE" == "" ]]; then
+ make
+fi