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OpenDTeX Secure Boot

Project Description

The OpenDTeX research project aims at providing trusted building blocks to ensure strong security properties during the boot chain and to allow secure execution of isolated enclaves on x86 architectures.

OpenDTeX has been achieved with the help of the French “RAPID <http://www.ixarm.com/Projets-d-innovation-duale-RAPID>_” grant process, which targets both civil and defense use cases, through a consortium composed of AMOSSYS, Bertin Technologies and Telecom ParisTech.

This project leverages TCG technologies, such as TPM and DRTM, to provide trusted execution of a minimal TCB (Trusted Computing Base). Besides, each building block can display proof of integrity up to the platform user, by implementing the concept of trusted banner, thus creating a trusted path between the user and the TCB.

The results of this project have been integrated in a Linux-based prototype, as well as in the PolyXene multi-level security operating system.

We provide here the implementation of the Secure Boot component in DRTM mode.

Authors and Sponsors

See the top distribution file AUTHORS.txt for the detailed and updated list of authors.

Project sponsors:

License

This software is licensed under the Modified BSD License. See the COPYING.txt file for the full license text.

More Information

   
Website https://github.com/AMOSSYS/OpenDTeX-Secure-Boot-DRTM
Email etudes@amossys.fr
Twitter Follow AMOSSYS's official accounts (@amossys)

OpenDTeX developments

OpenDTeX work notably include:

  • A TPM 1.2 API library independent from the BIOS or OS
  • A minimal TSS API library independent from the OS
  • A set of tools to manipulate the TPM.
  • An extension of Grub 2 (i.e. an SRTM implementation)
  • The implementation of a dedicated DRTM MLE extension (based on Trusted Boot)

Comparison with similar tools

  • Trusted Grub: this tool permits to extend the trust chain by measuring components that are executed beyond the BIOS, in SRTM mode.
  • Trusted Boot: this tool permits to start a new trust chain, in DRTM mode. Is also permits to verify the integrity of the Linux kernel and its associated initrd.
  • Bitlocker (in TPM mode): this tools allows to seal the master key with the TPM so that decryption is possible only if the platform integrity is correct. It only works through a SRTM (which means a large TCB).
  • Anti-Evil-Maid proof of concept from Joanna Rutkowska, which implements the concept of secure banner. This PoC only supports SRTM.

OpenDTeX Secure Boot allows both integrity verification and unsealing of boot time components, either in SRTM or DRTM mode. Besides, it provides explicit trust attestation to the user thanks to a shared secret (the secret banner).

Design of the Secure Boot in DRTM mode

DRTM implementation

Regarding the DRTM implementation, we rely on the Intel Trusted Boot extension combined with a dedicated MLE (Measured Launch Environment) extension. In Trusted Boot, the associated MLE is responsible for verifying the integrity of the Linux kernel and its initrd file by comparing their hash to a reference one. In OpenDTeX, this MLE is modified to integrate more functionalities (the secure banner, the unsealing of critical components, etc.). The MLE extension that is responsible for those new functionalities is called TLoader. We describe its architecture and usage in the current chapter, after a brief reminder regarding Trusted Boot.

Boot sequence of Trusted Boot

In Trusted Boot, the execution flow is as follow:

  • A DRTM sequence is initiated by the GETSEC[SENTER] instruction from the Intel SMX instruction set.
  • The processor measures and then executes an Intel-signed binary called SINIT AC, which is responsible for verifying that the platform is properly compatible and configured.
  • The SINIT AC measures and then executes a component called MLE (Measured Launch Environment), which acts as a secure loader. Trusted Boot provides its own MLE.
  • The Trusted Boot MLE finally measures the Linux kernel and its associated initrd and verifies that their hashes matches the reference ones. If this is the case, the execution flow is transferred to the Linux kernel.

Description of the TLoader

The OpenDTeX MLE extension, called TLoader, provides the following functionalities:

  • The capability to extend the DRTM trust chain.
  • The secure banner, to allow explicit local attestation of platform integrity to the user.
  • The unsealing of files, and especially the Linux kernel and the initrd, thus allowing to conditionnaly boot the platform if its integrity is conform.

The OpenDTeX TLoader currently supports the following commands, received through multiboot structure of Grub.

  • tpm_loadkey: loads a cryptographic key in the TPM volatile memory.
  • tpm_banner: unseals a secure banner (either a text or an image) and presents it to the user.
  • launch: loads a kernel in memory, measures its integrity and extends the result to a specific TPM PCR register.
  • initrd: loads an initrd file in memory, measures its integrity and extends the result to a specific TPM PCR register.
  • tpm_launch: loads an encrypted kernel in memory, unseals it, measures its integrity and extends the result to a specific TPM PCR register.
  • tpm_initrd: loads an encrypted initrd file in memory, unseals it, measures its integrity and extends the result to a specific TPM PCR register.
  • logging: specifies the logging verbosity level.

The Secure Banner

The secure banner principle intends to provide explicit local attestation of the platform integrity to the user. The secure banner is in fact a message or image only known from the user and encrypted with a TPM cryptographic key, so that it can only be decrypted if the platform integrity is what is expected by the user. Thus, this text or image have to be sealed in order to caracterize the integrity of the plateform. In other words, at boot time, if the secure banner can be unsealed, this means that the platform integrity is correct.

Hardware requirements

Secure Boot component requires some hardware support:

  • A TPM 1.2 (Trusted Platform Module).
  • A chipset that supports Intel TXT and IOMMU.
  • A processor that supports Intel TXT (through the SMX instruction set) and VT-x.

Basically, a platform that have an Intel VPro sticker should be compatible.

Besides those hardware requirements, they have to be activated in the BIOS.

Compilation and installation of the DRTM components

This chapter presents the different steps required to compile and install the OpenDTeX Secure Boot components in DRTM mode, which are:

  • libtpm: a library that provides an API to communicate with the TPM.
  • libuc: a library that provides basic libc functionalities such as memory and strings handling.
  • libuvideo: a library that provides direct access to the video card framebuffer.
  • libtxt: a library that exposes functionalities linked with the Intel SMX instruction set and management of TXT heap/registers.
  • Trusted Boot: we rely on Trusted Boot for the preparation and launch of the DRTM environemnt.
  • AC SINIT: a signed binary provided by Intel, which is responsible for verifying that the platform is properly compatible and configured.
  • Tloader: a library that implements a MLE (i.e. the component that is called by the AC SINIT during a DRTM) and provides services such as the secure banner and the unsealing of critical components.

Dependencies

In order to compile the OpenDTeX Secure Boot components, you should have:

  • make
  • gcc
  • autoconf
  • automake
  • m4
  • autotools-dev

Compilation and installation of libuc

In "libuc/":

$ ./autogen.sh
$ ./configure --prefix=/opt/ulib
$ make
$ sudo make install

Compilation and installation of uvideo

In "libuvideo/":

$ ./autogen.sh
$ PKG_CONFIG_PATH=/opt/ulib/lib/pkgconfig ./configure --prefix=/opt/ulib
$ make
$ sudo make install

Compilation and installation of libtpm

In "libtpm/":

$ ./autogen.sh
$ PKG_CONFIG_PATH=/opt/ulib/lib/pkgconfig ./configure --prefix=/opt/ulib
$ make
$ sudo make install

Compilation and installation of libtxt

In "libtxt/":

$ ./autogen.sh
$ PKG_CONFIG_PATH=/opt/ulib/lib/pkgconfig ./configure --prefix=/opt/ulib
$ make
$ sudo make install

Compilation and installation of Tloader

In "tloader/":

$ ./autogen.sh
$ PKG_CONFIG_PATH=/opt/ulib/lib/pkgconfig ./configure
$ make

This last step will generate a file tloader.gz. You have to place this file in the directory "/boot/".

Compilation and installation of Trusted Boot

Trusted Boot in available on Sourceforge: http://sourceforge.net/projects/tboot/

Once the archive has been downloaded, go inside the tboot/ directory, and then:

$ make
$ sudo make install

This last step will copy the file tboot.gz (the loader) in the directory "/boot/".

Deployment of the AC SINIT module

You have to retrieve the AC SINIT module that is compatible with your chipset/processor on Intel website: http://software.intel.com/en-us/articles/intel-trusted-execution-technology.

The AC SINIT module have to be copied in the directory "/boot/".

Preparation of the Secure Banner

Create a TPM key, such that it can be loaded again inside the TPM memory if the PCR1 and PCR2 have the same content that they had during key creation::

$ cd tools/
$ make
$ tcg_createkey -k | -z depth key1.key PCR1:PCR2

Seal a secret text message with this TPM key, and tell the TPM to seal the object so that it can be decrypted again if contents of PCR17, PCR18 and PCR19 have not changed::

$ echo "My secret message" > /tmp/test
$ python createStruct.py text /tmp/test > /tmp/test.data
$ ./tcg_seal -i /tmp/test.data -o data.seal -z -k key1.key -p 17:18:19
(0000)-> SRK(WellKnown : 1)
(0001)-> key1.key(WellKnown : 1)(00000000)
| child of SRK
symmetric key : b0 49 e5 34 9b f1 c5 59 d3 b5 82 03 58 68 9f a2 f1 ad e4 d3 1c dd 18 bb 01

Or seal a secret image::

$ python createStruct.py image zoby.bmp > /tmp/test.data
$ ./tcg_seal -i /tmp/test.data -o data.seal -z -k key1.key

Put the sealed data (either the message or the image) in the boot directory::

$ sudo mkdir /boot/opendtex/
$ sudo cp data.seal /boot/opendtex/data.seal

Configuration of Grub

Here is a Grub 2 configuration file example, that permits to launch Trusted Boot, then to execute a DRTM, and then to give execution flow to the TLoader MLE. The TLoader then interpret the command::

menuentry 'TBoot+TLoader' {
  # GRUB2 modules
  insmod gzio
  insmod part_msdos
  insmod ext2
  # To find system disk boot partition
  set root='(/dev/sda,msdos5)'
  search --no-floppy --fs-uuid --set=root 86cf0374-fbf3-4d36-9b5c-45303f24c17a

  # TrustedBoot main module to start
  multiboot /boot/tboot.gz /boot/tboot.gz logging=vga,memory,serial

  # The platform specific AC module
  module /boot/SINIT

  # TLoader module launched by TrustedBoot
  module /boot/tloader.gz /boot/tloader.gz logging=vga

  # Entry to display the secure banner (with a key to load)
  module /boot/opendtex/key1.key /boot/opendtex/key1.key tpm_loadkey aliasKey1 aliasSRK
  module /boot/opendtex/data.seal /boot/opendtex/data.seal tpm_banner aliasKey1

  # The OS image to start
  module /boot/vmlinuz /boot/vmlinuz kdb=fr vga=791 root=/dev/hda1 ...
  module /boot/initrd /boot/initrd
}

Now that the platform is correctly configured, the next time you start the system, a Secure Boot will be launched, meaning that many boot components will be measured, and if nothing has changed in terms of integrity, you will see the secure banner.

And if one boot component appears to have its integrity altered, you will get a error when the TPM attempts to unseal either the protected key or the protected object.

Acknowledgment

We would like to thanks people behind the following projects: