opal-kexec-pba

Alternative OPAL SED unlock image for pre-boot authentication (alternative to LinuxPBA).

Introduction

This repository contains some scripts for creating an initramfs and boot image to use as a PBA image on OPAL encrypted hard disk and solid state drives.

See Drive-Trust-Alliance/sedutil for a more detailed explanation of self-encrypting drives (SED) and how to use them with Linux.

Disclaimer

These scripts have only been tested on a single machine, with a specific NVME SED device, under UEFI. I won't be able to help you if it bricks your drive, nor will I take any responsibility for any errors or flaws in the scripts which may lead to ruined hard drives, leaked passwords or data, or anything other bad things.

Features

• Uses the kexec mechanism to launch the regular OS kernel (only tested on Linux).
• Faster boots since the UEFI firmware does not need to be executed twice
• Defer boot process to a shell script in /boot
• Provides optional warm reboot-method as an alternative if kexec is not possible (e.g. booting Windows)

Drawbacks

• No support for UEFI bootloaders such as rEFInd or GRUB2
• No menus
• Not well tested

Motivation

The LinuxPBA provided in the DTA/sedutil repo requires a reboot after unlocking in order to boot the regular OS, which can take a long time on some UEFI firmwares.

Dependencies

• sedutil-cli from sedutil
• busybox from busybox
• kexec from kexec-tools
• hdparm from hdparm

All deps need to be built as static binaries or manually add the necessary libraries. sedutil-cli is used to unlock the drive and hide the shadow MBR to show the real partitions. busybox provides the shell. kexec is used to load the kernel of regular OS and to execute it. hdparm (-z option) is used to tell the kernel of the pre-boot environment to re-read the partition table.

Usage

When booting with a self-encrypting drive, the real file system is hidden and a small partition is shown instead, this is sometimes called a shadow MBR. The shadow MBR contains a minimal boot loader and a small system for unlocking the drive. The boot loader I have used for this purpose is isolinux, copied from sedutil's LinuxPBA. isolinux will launch a small Linux system for unlocking the drive. The init script in this repository will run opal-unlock until it succeeds in unlocking at least one drive. After a drive has been unlocked, the init script will either do a warm reset (system reboot back to UEFI/BIOS), or pass execution on to a third stage boot loader named boot.sh. boot.sh is a regular shell script, and is located on one of the regular partitions of the drive (not in the shadow MBR area). This script allows us to customize the boot process further without having to re-flash the shadow PBA every time we do a kernel update or otherwise need to modify the boot.

An example boot.sh is provided in the scripts directory of this repo.

Quick recap:

Boot process with OPAL encrypted drive:

1. UEFI/BIOS
2. Start isolinux from shadow MBR
3. Run minimal Linux system, init script takes over
4. init calls sedutil to unlock the drive and unhide the normal partitions
5. (a) Either: Reboot back to UEFI/BIOS (b) Or: init mounts /boot
6. Pass execution on to /boot/boot.sh
7. boot.sh loads a kernel and initramfs from /boot (kexec -l)
8. boot.sh runs kexec -e to launch the full Linux system

Boot flags/kernel command-line

init handles only one command line option:

• boot=/dev/nvme0n1p1 - mount /dev/nvme0n1p1 as /boot before attempting to run /boot/boot.sh (at step 5b above)
• boot=reboot - reboot system after unlocking (at step 5a above)

The example boot.sh handles some more options:

• kernel=FILENAME - specify kernel filename to pass to kexec
• root=/dev/sda1 - specify root= option to pass to kexec'd kernel
• shell=1 - stop in an emergency shell before running kexec -e

Building initramfs and disk image

This is not scripted (yet, feel free to provide one), below is an outline on how to generate an image.

1. Create a local tree with all files for the initramfs
2. find . -print0 | cpio --null -ov --format=newc > ../unlock.cpio
3. xz -9 -C crc32 unlock.cpio
4. dd if=/dev/zero of=opal.gptdisk bs=1M count=32
5. gdisk opal.gptdisk
   • Create new partition table
   • Create new partition, default extents (whole "disk")
   • Type EF00
   • Set a parition name (might show up in the UEFI firmware boot menu)
   • o
   • n [enter],[enter],[enter]
   • t EF00
   • c Unlock drive
6. losetup -f --show -o 1048576 opal.gptdisk
7. mount [loopback device] /mnt/opal
8. Copy bootdisk/EFI to /mnt/opal/EFI (syslinux installation)
9. Copy isolinux bootx64.efi and ldlinux.e64 to /mnt/opal/EFI/Boot/
10. Put a known good kernel at /mnt/opal/EFI/Boot/bzImage
11. Place unlock.cpio.xz at /mnt/opal/EFI/Boot/unlock.cpio.xz
12. umount /mnt/opal

It is also possible to start with the LinuxPBA image instead of an empty image, mount it, and replace the syslinux.cfg, kernel bzImage, and initramfs.

The image generated above will only work on UEFI systems.

Building sedutil-cli as a static binary

Use the patch in patches/sedutil-static.patch to build sedutil-cli as a static binary.

Setting up /boot

Place boot.sh and warm-boot-conf.sh in /boot. Modify warm-boot-conf.sh with any settings you might need. The default behaviour is to let boot.sh search the whole /boot disk for any kernels and pick the one with the newest file modification date, which is most often the one we want to run.

Loading the PBA image into the shadow MBR

With the drive unlocked:

sedutil-cli --loadPBAimage password /path/to/opal.gptdisk /dev/nvme0n1

This takes a long time (several minutes for a few megabytes). Make a smaller drive image (dd step above) if you want it to go faster.

Testing

This has been tested on a single machine, with an Intel 6000p NVMe drive (SSDPEKKF512G7), using UEFI boot, Secure Boot disabled. I am using an image with these scripts as the primary unlock method on that machine and have been using this for a few weeks now (2016-12-05).

Example initramfs layout

├── bin/
│   └── busybox*
├── boot/
├── dev/
│   ├── console
│   ├── null
│   ├── tty
│   └── zero
├── etc/
├── init*
├── lib -> lib64/
├── lib64/
│   ├── ld-2.23.so*
│   ├── ld-linux-x86-64.so.2 -> ld-2.23.so*
│   ├── libc-2.23.so*
│   ├── libc.so.6 -> libc-2.23.so*
│   ├── liblzma.so.5 -> liblzma.so.5.2.2*
│   ├── liblzma.so.5.2.2*
│   ├── libpthread-2.23.so*
│   ├── libpthread.so.0 -> libpthread-2.23.so*
│   ├── libz.so.1 -> libz.so.1.2.8*
│   └── libz.so.1.2.8*
├── mnt/
│   └── root/
├── opal-unlock*
├── proc/
├── root/
├── sbin/
│   ├── hdparm*
│   ├── kexec*
│   └── sedutil-cli*
└── sys/