3. Setting up the boot device
3.1. Creating the ramdisk
To begin with, chroot inside the encrypted partition and create the boot device mount point:
chroot /mnt/efs mkdir /loader |
Then, create the initial ramdisk (initrd), which will be needed afterwards:
cd dd if=/dev/zero of=initrd bs=1k count=4096 mke2fs -F initrd mkdir ramdisk mount -o loop initrd ramdisk |
If you're using grsecurity, you may get a "Permission denied" error message; in this case you'll have to run the mount command outside chroot.
Create the filesystem hierarchy and copy the required files in it:
mkdir ramdisk/{bin,dev,lib,mnt,sbin}
cp /bin/{bash,mount} ramdisk/bin/
ln -s bash ramdisk/bin/sh
mknod -m 600 ramdisk/dev/console c 5 1
mknod -m 600 ramdisk/dev/hda2 b 3 2
mknod -m 600 ramdisk/dev/loop0 b 7 0
cp /lib/{ld-linux.so.2,libc.so.6,libdl.so.2} ramdisk/lib/
cp /lib/{libncurses.so.5,libtermcap.so.2} ramdisk/lib/
cp /sbin/{losetup,pivot_root} ramdisk/sbin/ |
It's ok if you see a message like "/lib/libncurses.so.5: No such file or directory", or "/lib/libtermcap.so.2: No such file or directory"; bash only requires one of these two libraries. You can check which one is actually required with:
ldd /bin/bash |
Compile the sleep program, which will prevent the password prompt being flooded by kernel messages (such as usb devices being registered).
cat > sleep.c << "EOF"
#include <unistd.h>
#include <stdlib.h>
int main( int argc, char *argv[] )
{
if( argc == 2 )
sleep( atoi( argv[1] ) );
return( 0 );
}
EOF
gcc -s sleep.c -o ramdisk/bin/sleep
rm sleep.c |
Create the init script:
cat > ramdisk/sbin/init << "EOF"
#!/bin/sh
/bin/sleep 3
echo -n "Enter seed value: "
read SEED
/sbin/losetup -e aes256 -S $SEED /dev/loop0 /dev/hda2
/bin/mount -r -n -t ext3 /dev/loop0 /mnt
while [ $? -ne 0 ]
do
/sbin/losetup -d /dev/loop0
/sbin/losetup -e aes256 -S $SEED /dev/loop0 /dev/hda2
/bin/mount -r -n -t ext3 /dev/loop0 /mnt
done
cd /mnt
/sbin/pivot_root . loader
exec /usr/sbin/chroot . /sbin/init
EOF
chmod 755 ramdisk/sbin/init |
Umount the loopback device and compress the initrd:
umount -d ramdisk rmdir ramdisk gzip initrd mv initrd.gz /boot/ |
3.2. Booting from a CD-ROM
I strongly advise you to start your system with a read-only media, such as a bootable CD-ROM.
Download and unpack syslinux:
wget http://ftp.kernel.org/pub/linux/utils/boot/syslinux/syslinux-3.07.tar.bz2 tar -xvjf syslinux-3.07.tar.bz2 |
Configure isolinux:
mkdir bootcd
cp /boot/{vmlinuz,initrd.gz} syslinux-3.07/isolinux.bin bootcd
echo "DEFAULT /vmlinuz initrd=initrd.gz ro root=/dev/ram0" \
> bootcd/isolinux.cfg |
Create and burn the bootable cd-rom iso image:
mkisofs -o bootcd.iso -b isolinux.bin -c boot.cat \
-no-emul-boot -boot-load-size 4 -boot-info-table \
-J -hide-rr-moved -R bootcd/
cdrecord -dev 0,0,0 -speed 4 -v bootcd.iso
rm -rf bootcd{,.iso} |
3.3. Booting from a HD partition
The boot partition can come in handy if you happen to lose your bootable CD. Remember that hda1 is a writable media and is thus insecure; use it only in case of emergency!
Create and mount the ext2 filesystem:
dd if=/dev/zero of=/dev/hda1 bs=8192 mke2fs /dev/hda1 mount /dev/hda1 /loader |
Copy the kernel and the initial ramdisk:
cp /boot/{vmlinuz,initrd.gz} /loader |
If you use grub:
mkdir /loader/boot
cp -av /boot/grub /loader/boot/
cat > /loader/boot/grub/menu.lst << EOF
default 0
timeout 10
color green/black light-green/black
title Linux
root (hd0,0)
kernel /vmlinuz ro root=/dev/ram0
initrd /initrd.gz
EOF
grub-install --root-directory=/loader /dev/hda
umount /loader |
If you use lilo:
mkdir /loader/{boot,dev,etc}
cp /boot/boot.b /loader/boot/
mknod -m 600 /loader/dev/hda b 3 0
mknod -m 600 /loader/dev/hda1 b 3 1
mknod -m 600 /loader/dev/hda2 b 3 2
mknod -m 600 /loader/dev/hda3 b 3 3
mknod -m 600 /loader/dev/hda4 b 3 4
mknod -m 600 /loader/dev/ram0 b 1 0
cat > /loader/etc/lilo.conf << EOF
lba32
boot=/dev/hda
prompt
timeout=60
image=/vmlinuz
label=Linux
initrd=/initrd.gz
read-only
root=/dev/ram0
EOF
lilo -r /loader
umount /loader |