x86, intel_txt: Intel TXT boot support

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 http://www.intel.com/technology/security/.

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:

          http://www.linuxtag.org/2008/en/conf/events/vp-donnerstag/

          details.html?talkid=110

      TRUST2008:

          http://www.trust2008.eu/downloads/Keynote-Speakers/

          3_David-Grawrock_The-Front-Door-of-Trusted-Computing.pdf

      IDF 2008, Shanghai:

          http://inteldeveloperforum.com.edgesuite.net/shanghai_2008/

          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

kernel/VMM.

It is hosted on SourceForge at http://sourceforge.net/projects/tboot.

The mercurial source repo is available at http://www.bughost.org/

repos.hg/tboot.hg.

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.

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!!

struct boot_params {

	struct screen_info screen_info;			/* 0x000 */

	struct apm_bios_info apm_bios_info;		/* 0x040 */

	__u8  _pad2[12];				/* 0x054 */

	__u8  _pad2[4];					/* 0x054 */

	__u64  tboot_addr;				/* 0x058 */

	struct ist_info ist_info;			/* 0x060 */

	__u8  _pad3[16];				/* 0x070 */

	__u8  hd0_info[16];	/* obsolete! */		/* 0x080 */

#endif

#ifdef CONFIG_X86_32

	FIX_WP_TEST,

#endif

#ifdef CONFIG_INTEL_TXT

	FIX_TBOOT_BASE,

#endif

	__end_of_fixed_addresses

};

/*

 * tboot.h: shared data structure with tboot and kernel and functions

 *          used by kernel for runtime support of Intel(R) Trusted

 *          Execution Technology

 *

 * Copyright (c) 2006-2009, Intel Corporation

 *

 * This program is free software; you can redistribute it and/or modify it

 * under the terms and conditions of the GNU General Public License,

 * version 2, as published by the Free Software Foundation.

 *

 * This program is distributed in the hope it will be useful, but WITHOUT

 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or

 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for

 * more details.

 *

 * You should have received a copy of the GNU General Public License along with

 * this program; if not, write to the Free Software Foundation, Inc.,

 * 51 Franklin St - Fifth Floor, Boston, MA 02110-1301 USA.

 *

 */

#ifndef _ASM_TBOOT_H

#define _ASM_TBOOT_H

#include <acpi/acpi.h>

/* these must have the values from 0-5 in this order */

enum {

	TB_SHUTDOWN_REBOOT = 0,

	TB_SHUTDOWN_S5,

	TB_SHUTDOWN_S4,

	TB_SHUTDOWN_S3,

	TB_SHUTDOWN_HALT,

	TB_SHUTDOWN_WFS

};

#ifdef CONFIG_INTEL_TXT

/* used to communicate between tboot and the launched kernel */

#define TB_KEY_SIZE             64   /* 512 bits */

#define MAX_TB_MAC_REGIONS      32

struct tboot_mac_region {

	u64  start;         /* must be 64 byte -aligned */

	u32  size;          /* must be 64 byte -granular */

} __packed;

/* GAS - Generic Address Structure (ACPI 2.0+) */

struct tboot_acpi_generic_address {

	u8  space_id;

	u8  bit_width;

	u8  bit_offset;

	u8  access_width;

	u64 address;

} __packed;

/*

 * combines Sx info from FADT and FACS tables per ACPI 2.0+ spec

 * (http://www.acpi.info/)

 */

struct tboot_acpi_sleep_info {

	struct tboot_acpi_generic_address pm1a_cnt_blk;

	struct tboot_acpi_generic_address pm1b_cnt_blk;

	struct tboot_acpi_generic_address pm1a_evt_blk;

	struct tboot_acpi_generic_address pm1b_evt_blk;

	u16 pm1a_cnt_val;

	u16 pm1b_cnt_val;

	u64 wakeup_vector;

	u32 vector_width;

	u64 kernel_s3_resume_vector;

} __packed;

/*

 * shared memory page used for communication between tboot and kernel

 */

struct tboot {

	/*

	 * version 3+ fields:

	 */

	/* TBOOT_UUID */

	u8 uuid[16];

	/* version number: 5 is current */

	u32 version;

	/* physical addr of tb_log_t log */

	u32 log_addr;

	/*

	 * physical addr of entry point for tboot shutdown and

	 * type of shutdown (TB_SHUTDOWN_*) being requested

	 */

	u32 shutdown_entry;

	u32 shutdown_type;

	/* kernel-specified ACPI info for Sx shutdown */

	struct tboot_acpi_sleep_info acpi_sinfo;

	/* tboot location in memory (physical) */

	u32 tboot_base;

	u32 tboot_size;

	/* memory regions (phys addrs) for tboot to MAC on S3 */

	u8 num_mac_regions;

	struct tboot_mac_region mac_regions[MAX_TB_MAC_REGIONS];

	/*

	 * version 4+ fields:

	 */

	/* symmetric key for use by kernel; will be encrypted on S3 */

	u8 s3_key[TB_KEY_SIZE];

	/*

	 * version 5+ fields:

	 */

	/* used to 4byte-align num_in_wfs */

	u8 reserved_align[3];

	/* number of processors in wait-for-SIPI */

	u32 num_in_wfs;

} __packed;

/*

 * UUID for tboot data struct to facilitate matching

 * defined as {663C8DFF-E8B3-4b82-AABF-19EA4D057A08} by tboot, which is

 * represented as {} in the char array used here

 */

#define TBOOT_UUID	{0xff, 0x8d, 0x3c, 0x66, 0xb3, 0xe8, 0x82, 0x4b, 0xbf,\

			 0xaa, 0x19, 0xea, 0x4d, 0x5, 0x7a, 0x8}

extern struct tboot *tboot;

static inline int tboot_enabled(void)

{

	return tboot != NULL;

}

extern void tboot_probe(void);

extern void tboot_create_trampoline(void);

extern void tboot_shutdown(u32 shutdown_type);

extern void tboot_sleep(u8 sleep_state, u32 pm1a_control, u32 pm1b_control);

extern int tboot_wait_for_aps(int num_aps);

extern struct acpi_table_header *tboot_get_dmar_table(

				      struct acpi_table_header *dmar_tbl);

extern int tboot_force_iommu(void);

#else     /* CONFIG_INTEL_TXT */

static inline int tboot_enabled(void)

{

	return 0;

}

static inline void tboot_probe(void)

{

}

static inline void tboot_create_trampoline(void)

{

}

static inline void tboot_shutdown(u32 shutdown_type)

{

}

static inline void tboot_sleep(u8 sleep_state, u32 pm1a_control,

			       u32 pm1b_control)

{

}

static inline int tboot_wait_for_aps(int num_aps)

{

	return 0;

}

static inline struct acpi_table_header *tboot_get_dmar_table(

					struct acpi_table_header *dmar_tbl)

{

	return dmar_tbl;

}

static inline int tboot_force_iommu(void)

{

	return 0;

}

#endif /* !CONFIG_INTEL_TXT */

#endif /* _ASM_TBOOT_H */