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+Intel(R) TXT Overview:
+Intel's technology for safer computing, Intel(R) Trusted Execution
+Technology (Intel(R) TXT), defines platform-level enhancements that
+provide the building blocks for creating trusted platforms.
+Intel TXT was formerly known by the code name LaGrande Technology (LT).
+Intel TXT in Brief:
+o Provides dynamic root of trust for measurement (DRTM)
+o Data protection in case of improper shutdown
+o Measurement and verification of launched environment
+Intel TXT is part of the vPro(TM) brand and is also available some
+non-vPro systems. It is currently available on desktop systems
+based on the Q35, X38, Q45, and Q43 Express chipsets (e.g. Dell
+Optiplex 755, HP dc7800, etc.) and mobile systems based on the GM45,
+PM45, and GS45 Express chipsets.
+For more information, see
+This site also has a link to the Intel TXT MLE Developers Manual,
+which has been updated for the new released platforms.
+Intel TXT has been presented at various events over the past few
+years, some of which are:
+ LinuxTAG 2008:
+ details.html?talkid=110
+ TRUST2008:
+ 3_David-Grawrock_The-Front-Door-of-Trusted-Computing.pdf
+ IDF 2008, Shanghai:
+ aep/PROS003/index.html
+ IDFs 2006, 2007 (I'm not sure if/where they are online)
+Trusted Boot Project Overview:
+Trusted Boot (tboot) is an open source, pre- kernel/VMM module that
+uses Intel TXT to perform a measured and verified launch of an OS
+It is hosted on SourceForge at
+The mercurial source repo is available at
+Tboot currently supports launching Xen (open source VMM/hypervisor
+w/ TXT support since v3.2), and now Linux kernels.
+Value Proposition for Linux or "Why should you care?"
+While there are many products and technologies that attempt to
+measure or protect the integrity of a running kernel, they all
+assume the kernel is "good" to begin with. The Integrity
+Measurement Architecture (IMA) and Linux Integrity Module interface
+are examples of such solutions.
+To get trust in the initial kernel without using Intel TXT, a
+static root of trust must be used. This bases trust in BIOS
+starting at system reset and requires measurement of all code
+executed between system reset through the completion of the kernel
+boot as well as data objects used by that code. In the case of a
+Linux kernel, this means all of BIOS, any option ROMs, the
+bootloader and the boot config. In practice, this is a lot of
+code/data, much of which is subject to change from boot to boot
+(e.g. changing NICs may change option ROMs). Without reference
+hashes, these measurement changes are difficult to assess or
+confirm as benign. This process also does not provide DMA
+protection, memory configuration/alias checks and locks, crash
+protection, or policy support.
+By using the hardware-based root of trust that Intel TXT provides,
+many of these issues can be mitigated. Specifically: many
+pre-launch components can be removed from the trust chain, DMA
+protection is provided to all launched components, a large number
+of platform configuration checks are performed and values locked,
+protection is provided for any data in the event of an improper
+shutdown, and there is support for policy-based execution/verification.
+This provides a more stable measurement and a higher assurance of
+system configuration and initial state than would be otherwise
+possible. Since the tboot project is open source, source code for
+almost all parts of the trust chain is available (excepting SMM and
+Intel-provided firmware).
+How Does it Work?
+o Tboot is an executable that is launched by the bootloader as
+ the "kernel" (the binary the bootloader executes).
+o It performs all of the work necessary to determine if the
+ platform supports Intel TXT and, if so, executes the GETSEC[SENTER]
+ processor instruction that initiates the dynamic root of trust.
+ - If tboot determines that the system does not support Intel TXT
+ or is not configured correctly (e.g. the SINIT AC Module was
+ incorrect), it will directly launch the kernel with no changes
+ to any state.
+ - Tboot will output various information about its progress to the
+ terminal, serial port, and/or an in-memory log; the output
+ locations can be configured with a command line switch.
+o The GETSEC[SENTER] instruction will return control to tboot and
+ tboot then verifies certain aspects of the environment (e.g. TPM NV
+ lock, e820 table does not have invalid entries, etc.).
+o It will wake the APs from the special sleep state the GETSEC[SENTER]
+ instruction had put them in and place them into a wait-for-SIPI
+ state.
+ - Because the processors will not respond to an INIT or SIPI when
+ in the TXT environment, it is necessary to create a small VT-x
+ guest for the APs. When they run in this guest, they will
+ simply wait for the INIT-SIPI-SIPI sequence, which will cause
+ VMEXITs, and then disable VT and jump to the SIPI vector. This
+ approach seemed like a better choice than having to insert
+ special code into the kernel's MP wakeup sequence.
+o Tboot then applies an (optional) user-defined launch policy to
+ verify the kernel and initrd.
+ - This policy is rooted in TPM NV and is described in the tboot
+ project. The tboot project also contains code for tools to
+ create and provision the policy.
+ - Policies are completely under user control and if not present
+ then any kernel will be launched.
+ - Policy action is flexible and can include halting on failures
+ or simply logging them and continuing.
+o Tboot adjusts the e820 table provided by the bootloader to reserve
+ its own location in memory as well as to reserve certain other
+ TXT-related regions.
+o As part of it's launch, tboot DMA protects all of RAM (using the
+ VT-d PMRs). Thus, the kernel must be booted with 'intel_iommu=on'
+ in order to remove this blanket protection and use VT-d's
+ page-level protection.
+o Tboot will populate a shared page with some data about itself and
+ pass this to the Linux kernel as it transfers control.
+ - The location of the shared page is passed via the boot_params
+ struct as a physical address.
+o The kernel will look for the tboot shared page address and, if it
+ exists, map it.
+o As one of the checks/protections provided by TXT, it makes a copy
+ of the VT-d DMARs in a DMA-protected region of memory and verifies
+ them for correctness. The VT-d code will detect if the kernel was
+ launched with tboot and use this copy instead of the one in the
+ ACPI table.
+o At this point, tboot and TXT are out of the picture until a
+ shutdown (S<n>)
+o In order to put a system into any of the sleep states after a TXT
+ launch, TXT must first be exited. This is to prevent attacks that
+ attempt to crash the system to gain control on reboot and steal
+ data left in memory.
+ - The kernel will perform all of its sleep preparation and
+ populate the shared page with the ACPI data needed to put the
+ platform in the desired sleep state.
+ - Then the kernel jumps into tboot via the vector specified in the
+ shared page.
+ - Tboot will clean up the environment and disable TXT, then use the
+ kernel-provided ACPI information to actually place the platform
+ into the desired sleep state.
+ - In the case of S3, tboot will also register itself as the resume
+ vector. This is necessary because it must re-establish the
+ measured environment upon resume. Once the TXT environment
+ has been restored, it will restore the TPM PCRs and then
+ transfer control back to the kernel's S3 resume vector.
+ In order to preserve system integrity across S3, the kernel
+ provides tboot with a set of memory ranges (kernel
+ code/data/bss, S3 resume code, and AP trampoline) that tboot
+ will calculate a MAC (message authentication code) over and then
+ seal with the TPM. On resume and once the measured environment
+ has been re-established, tboot will re-calculate the MAC and
+ verify it against the sealed value. Tboot's policy determines
+ what happens if the verification fails.
+That's pretty much it for TXT support.
+Configuring the System:
+This code works with 32bit, 32bit PAE, and 64bit (x86_64) kernels.
+In BIOS, the user must enable: TPM, TXT, VT-x, VT-d. Not all BIOSes
+allow these to be individually enabled/disabled and the screens in
+which to find them are BIOS-specific.
+grub.conf needs to be modified as follows:
+ title Linux 2.6.29-tip w/ tboot
+ root (hd0,0)
+ kernel /tboot.gz logging=serial,vga,memory
+ module /vmlinuz-2.6.29-tip intel_iommu=on ro
+ root=LABEL=/ rhgb console=ttyS0,115200 3
+ module /initrd-2.6.29-tip.img
+ module /Q35_SINIT_17.BIN
+The kernel option for enabling Intel TXT support is found under the
+Security top-level menu and is called "Enable Intel(R) Trusted
+Execution Technology (TXT)". It is marked as EXPERIMENTAL and
+depends on the generic x86 support (to allow maximum flexibility in
+kernel build options), since the tboot code will detect whether the
+platform actually supports Intel TXT and thus whether any of the
+kernel code is executed.
+The Q35_SINIT_17.BIN file is what Intel TXT refers to as an
+Authenticated Code Module. It is specific to the chipset in the
+system and can also be found on the Trusted Boot site. It is an
+(unencrypted) module signed by Intel that is used as part of the
+DRTM process to verify and configure the system. It is signed
+because it operates at a higher privilege level in the system than
+any other macrocode and its correct operation is critical to the
+establishment of the DRTM. The process for determining the correct
+SINIT ACM for a system is documented in the SINIT-guide.txt file
+that is on the tboot SourceForge site under the SINIT ACM downloads.