path: root/Documentation
diff options
authorJoseph Cihula <>2009-06-30 19:30:59 -0700
committerH. Peter Anvin <>2009-07-21 11:49:06 -0700
commit3162534069597e34dd0ac9eb711be8dc23835ae7 (patch)
treea8cddd3899917784ebac2cdf6c75d2c8b50d04af /Documentation
parentaea1f7964ae6cba5eb419a958956deb9016b3341 (diff)
x86, intel_txt: Intel TXT boot support
This patch adds kernel configuration and boot support for Intel Trusted Execution Technology (Intel TXT). Intel's technology for safer computing, Intel Trusted Execution Technology (Intel 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. A much more complete description of how these patches support TXT, how to configure a system for it, etc. is in the Documentation/intel_txt.txt file in this patch. This patch provides the TXT support routines for complete functionality, documentation for TXT support and for the changes to the boot_params structure, and boot detection of a TXT launch. Attempts to shutdown (reboot, Sx) the system will result in platform resets; subsequent patches will support these shutdown modes properly. Documentation/intel_txt.txt | 210 +++++++++++++++++++++ Documentation/x86/zero-page.txt | 1 arch/x86/include/asm/bootparam.h | 3 arch/x86/include/asm/fixmap.h | 3 arch/x86/include/asm/tboot.h | 197 ++++++++++++++++++++ arch/x86/kernel/Makefile | 1 arch/x86/kernel/setup.c | 4 arch/x86/kernel/tboot.c | 379 +++++++++++++++++++++++++++++++++++++++ security/Kconfig | 30 +++ 9 files changed, 827 insertions(+), 1 deletion(-) Signed-off-by: Joseph Cihula <> Signed-off-by: Shane Wang <> Signed-off-by: Gang Wei <> Signed-off-by: H. Peter Anvin <>
Diffstat (limited to 'Documentation')
2 files changed, 211 insertions, 0 deletions
diff --git a/Documentation/intel_txt.txt b/Documentation/intel_txt.txt
new file mode 100644
index 000000000000..f40a1f030019
--- /dev/null
+++ b/Documentation/intel_txt.txt
@@ -0,0 +1,210 @@
+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.
diff --git a/Documentation/x86/zero-page.txt b/Documentation/x86/zero-page.txt
index 4f913857b8a2..feb37e177010 100644
--- a/Documentation/x86/zero-page.txt
+++ b/Documentation/x86/zero-page.txt
@@ -12,6 +12,7 @@ Offset Proto Name Meaning
000/040 ALL screen_info Text mode or frame buffer information
(struct screen_info)
040/014 ALL apm_bios_info APM BIOS information (struct apm_bios_info)
+058/008 ALL tboot_addr Physical address of tboot shared page
060/010 ALL ist_info Intel SpeedStep (IST) BIOS support information
(struct ist_info)
080/010 ALL hd0_info hd0 disk parameter, OBSOLETE!!