108 lines
3.4 KiB
Bash
108 lines
3.4 KiB
Bash
#!/bin/bash
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#utilties for reading shim disk images
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run_binwalk() {
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if binwalk -h | grep -- '--run-as' >/dev/null; then
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binwalk "$@" --run-as=root
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else
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binwalk "$@"
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fi
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}
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extract_initramfs() {
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local kernel_bin="$1"
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local working_dir="$2"
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local output_dir="$3"
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#extract the compressed kernel image from the partition data
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local kernel_file="$(basename $kernel_bin)"
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local binwalk_out=$(run_binwalk --extract $kernel_bin --directory=$working_dir)
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local stage1_file=$(echo $binwalk_out | pcregrep -o1 "\d+\s+0x([0-9A-F]+)\s+gzip compressed data")
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local stage1_dir="$working_dir/_$kernel_file.extracted"
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local stage1_path="$stage1_dir/$stage1_file"
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#extract the initramfs cpio archive from the kernel image
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run_binwalk --extract $stage1_path --directory=$stage1_dir > /dev/null
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local stage2_dir="$stage1_dir/_$stage1_file.extracted/"
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local cpio_file=$(file $stage2_dir/* | pcregrep -o1 "([0-9A-F]+):\s+ASCII cpio archive")
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local cpio_path="$stage2_dir/$cpio_file"
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rm -rf $output_dir
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cat $cpio_path | cpio -D $output_dir -imd --quiet
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}
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extract_initramfs_arm() {
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local kernel_bin="$1"
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local working_dir="$2"
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local output_dir="$3"
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#extract the kernel lz4 archive from the partition
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local binwalk_out="$(run_binwalk $kernel_bin)"
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local lz4_offset="$(echo "$binwalk_out" | pcregrep -o1 "(\d+).+?LZ4 compressed data" | head -n1)"
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local lz4_file="$working_dir/kernel.lz4"
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local kernel_img="$working_dir/kernel_decompressed.bin"
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dd if=$kernel_bin of=$lz4_file iflag=skip_bytes,count_bytes skip=$lz4_offset status=none
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lz4 -d $lz4_file $kernel_img -q || true
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#extract the initramfs cpio archive from the kernel image
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local extracted_dir="$working_dir/_kernel_decompressed.bin.extracted"
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run_binwalk --extract $kernel_img --directory=$working_dir > /dev/null
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local cpio_file=$(file $extracted_dir/* | pcregrep -o1 "([0-9A-F]+):\s+ASCII cpio archive")
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local cpio_path="$extracted_dir/$cpio_file"
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rm -rf $output_dir
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cat $cpio_path | cpio -D $output_dir -imd --quiet
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}
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create_loop() {
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local loop_device=$(losetup -f)
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if [ ! -b "$loop_device" ]; then
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#we might run out of loop devices, see https://stackoverflow.com/a/66020349
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local major=$(grep loop /proc/devices | cut -c3)
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local number="$(echo "$loop_device" | grep -Eo '[0-9]+' | tail -n1)"
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mknod $loop_device b $major $number
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fi
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losetup -P $loop_device "${1}"
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echo $loop_device
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}
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copy_kernel() {
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local shim_path="$1"
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local kernel_dir="$2"
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local shim_loop=$(create_loop "${shim_path}")
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local kernel_loop="${shim_loop}p2" #KERN-A should always be p2
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dd if=$kernel_loop of=$kernel_dir/kernel.bin bs=1M status=none
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dd if=$kernel_loop of="/tmp/kernel.bin" bs=1M status=none
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# losetup -d $shim_loop
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}
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#copy the kernel image then extract the initramfs
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extract_initramfs_full() {
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local shim_path="$1"
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local rootfs_dir="$2"
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local kernel_bin="$3"
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local arch="$4"
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local kernel_dir=/tmp/shim_kernel
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echo "copying the shim kernel"
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rm -rf $kernel_dir
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mkdir $kernel_dir -p
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copy_kernel $shim_path $kernel_dir
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echo "extracting initramfs from kernel (this may take a while)"
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if [ "$arch" = "aarch64" ]; then
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extract_initramfs_arm $kernel_dir/kernel.bin $kernel_dir $rootfs_dir
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else
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extract_initramfs $kernel_dir/kernel.bin $kernel_dir $rootfs_dir
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fi
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if [ "$kernel_bin" ]; then
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cp $kernel_dir/kernel.bin $kernel_bin
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fi
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rm -rf $kernel_dir
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}
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