backup with dd
dd if=/dev/block/mmcblk0 of=/storage/sdcard1/boot.img bs=4096 count=4096 skip=7552
dd if=/dev/block/mmcblk0 of=/storage/sdcard1/recovery.img bs=4096 count=4096 skip=11648
fash boot.img with dd
dd if=/sdcard/image-new.img of=/dev/block/platform/155a0000.ufs/by-name/BOOT