[PATCH v10 01/20] Documentation/x86: Secure Launch kernel documentation
Ross Philipson
ross.philipson at oracle.com
Mon Aug 26 15:42:22 PDT 2024
From: "Daniel P. Smith" <dpsmith at apertussolutions.com>
Introduce background, overview and configuration/ABI information
for the Secure Launch kernel feature.
Signed-off-by: Daniel P. Smith <dpsmith at apertussolutions.com>
Signed-off-by: Ross Philipson <ross.philipson at oracle.com>
Reviewed-by: Bagas Sanjaya <bagasdotme at gmail.com>
---
Documentation/security/index.rst | 1 +
.../security/launch-integrity/index.rst | 11 +
.../security/launch-integrity/principles.rst | 320 ++++++++++
.../secure_launch_details.rst | 587 ++++++++++++++++++
.../secure_launch_overview.rst | 227 +++++++
5 files changed, 1146 insertions(+)
create mode 100644 Documentation/security/launch-integrity/index.rst
create mode 100644 Documentation/security/launch-integrity/principles.rst
create mode 100644 Documentation/security/launch-integrity/secure_launch_details.rst
create mode 100644 Documentation/security/launch-integrity/secure_launch_overview.rst
diff --git a/Documentation/security/index.rst b/Documentation/security/index.rst
index 59f8fc106cb0..56e31fb3d91f 100644
--- a/Documentation/security/index.rst
+++ b/Documentation/security/index.rst
@@ -19,3 +19,4 @@ Security Documentation
digsig
landlock
secrets/index
+ launch-integrity/index
diff --git a/Documentation/security/launch-integrity/index.rst b/Documentation/security/launch-integrity/index.rst
new file mode 100644
index 000000000000..838328186dd2
--- /dev/null
+++ b/Documentation/security/launch-integrity/index.rst
@@ -0,0 +1,11 @@
+=====================================
+System Launch Integrity documentation
+=====================================
+
+.. toctree::
+ :maxdepth: 1
+
+ principles
+ secure_launch_overview
+ secure_launch_details
+
diff --git a/Documentation/security/launch-integrity/principles.rst b/Documentation/security/launch-integrity/principles.rst
new file mode 100644
index 000000000000..d6d95099dfad
--- /dev/null
+++ b/Documentation/security/launch-integrity/principles.rst
@@ -0,0 +1,320 @@
+.. SPDX-License-Identifier: GPL-2.0
+.. Copyright © 2019-2024 Daniel P. Smith <dpsmith at apertussolutions.com>
+
+=======================
+System Launch Integrity
+=======================
+
+:Author: Daniel P. Smith
+:Date: August 2024
+
+This document serves to establish a common understanding of what is system
+launch, the integrity concern for system launch, and why using a Root of Trust
+(RoT) from a Dynamic Launch may be desired. Throughout this document
+terminology from the Trusted Computing Group (TCG) and National Institute for
+Science and Technology (NIST) is used to ensure a vendor natural language is
+used to describe and reference security-related concepts.
+
+System Launch
+=============
+
+There is a tendency to only consider the classical power-on boot as the only
+means to launch an Operating System (OS) on a computer system, but in fact most
+modern processors support two methods to launch the system. To provide clarity
+a common definition of a system launch should be established. This definition
+is that a during a single power life cycle of a system, a System Launch
+consists of an initialization event, typically in hardware, that is followed by
+an executing software payload that takes the system from the initialized state
+to a running state. Driven by the Trusted Computing Group (TCG) architecture,
+modern processors are able to support two methods to launch a system, these two
+types of system launch are known as Static Launch and Dynamic Launch.
+
+Static Launch
+-------------
+
+Static launch is the system launch associated with the power cycle of the CPU.
+Thus, static launch refers to the classical power-on boot where the
+initialization event is the release of the CPU from reset and the system
+firmware is the software payload that brings the system up to a running state.
+Since static launch is the system launch associated with the beginning of the
+power lifecycle of a system, it is therefore a fixed, one-time system launch.
+It is because of this that static launch is referred to and thought of as being
+"static".
+
+Dynamic Launch
+--------------
+
+Modern CPUs architectures provides a mechanism to re-initialize the system to a
+"known good" state without requiring a power event. This re-initialization
+event is the event for a dynamic launch and is referred to as the Dynamic
+Launch Event (DLE). The DLE functions by accepting a software payload, referred
+to as the Dynamic Configuration Environment (DCE), that execution is handed to
+after the DLE is invoked. The DCE is responsible for bringing the system back
+to a running state. Since the dynamic launch is not tied to a power event like
+the static launch, this enables a dynamic launch to be initiated at any time
+and multiple times during a single power life cycle. This dynamism is the
+reasoning behind referring to this system launch as being dynamic.
+
+Because a dynamic launch can be conducted at any time during a single power
+life cycle, they are classified into one of two types, an early launch or a
+late launch.
+
+:Early Launch: When a dynamic launch is used as a transition from a static
+ launch chain to the final Operating System.
+
+:Late Launch: The usage of a dynamic launch by an executing Operating System to
+ transition to a “known good” state to perform one or more operations, e.g. to
+ launch into a new Operating System.
+
+System Integrity
+================
+
+A computer system can be considered a collection of mechanisms that work
+together to produce a result. The assurance that the mechanisms are functioning
+correctly and producing the expected result is the integrity of the system. To
+ensure a system's integrity there are a subset of these mechanisms, commonly
+referred to as security mechanisms, that are present to help ensure the system
+produces the expected result or at least detect the potential of an unexpected
+result may have happened. Since the security mechanisms are relied upon to
+ensue the integrity of the system, these mechanisms are trusted. Upon
+inspection these security mechanisms each have a set of properties and these
+properties can be evaluated to determine how susceptible a mechanism might be
+to failure. This assessment is referred to as the Strength of Mechanism and for
+trusted mechanism enables for the trustworthiness of that mechanism to be
+quantified.
+
+For software systems, there are two system states for which the integrity is
+critical, when the software is loaded into memory and when the software is
+executing on the hardware. Ensuring that the expected software is load into
+memory is referred to as load-time integrity while ensuring that the software
+executing is the expected software is the runtime integrity of that software.
+
+Load-time Integrity
+-------------------
+
+It is critical to understand what load-time integrity establishes about a
+system and what is assumed, i.e. what is being trusted. Load-time integrity is
+when a trusted entity, i.e. an entity with an assumed integrity, takes an
+action to assess an entity being loaded into memory before it is used. A
+variety of mechanisms may be used to conduct the assessment, each with
+different properties. A particular property is whether the mechanism creates an
+evidence of the assessment. Often either cryptographic signature checking or
+hashing are the common assessment operations used.
+
+A signature checking assessment functions by requiring a representation of the
+accepted authorities and uses those representations to assess if the entity has
+been signed by an accepted authority. The benefit to this process is that
+assessment process includes an adjudication of the assessment. The drawbacks
+are that 1) the adjudication is susceptible to tampering by the Trusted
+Computing Base (TCB), 2) there is no evidence to assert that an untampered
+adjudication was completed, and 3) the system must be an active participant in
+the key management infrastructure.
+
+A cryptographic hashing assessment does not adjudicate the assessment but
+instead, generates evidence of the assessment to be adjudicated independently.
+The benefits to this approach is that the assessment may be simple such that it
+may be implemented in an immutable mechanism, e.g. in hardware. Additionally,
+it is possible for the adjudication to be conducted where it cannot be tampered
+with by the TCB. The drawback is that a compromised environment will be allowed
+to execute until an adjudication can be completed.
+
+Ultimately, load-time integrity provides confidence that the correct entity was
+loaded and in the absence of a run-time integrity mechanism assumes, i.e.
+trusts, that the entity will never become corrupted.
+
+Runtime Integrity
+-----------------
+
+Runtime integrity in the general sense is when a trusted entity makes an
+assessment of an entity at any point in time during the assessed entity's
+execution. A more concrete explanation is the taking of an integrity assessment
+of an active process executing on the system at any point during the process'
+execution. Often the load-time integrity of an operating system's user-space,
+i.e. the operating environment, is confused to be the runtime integrity of the
+system, since it is an integrity assessment of the "runtime" software. The
+reality is that actual runtime integrity is a very difficult problem and thus
+not very many solutions are public and/or available. One example of a runtime
+integrity solution would be Johns Hopkins Advanced Physics Laboratory's (APL)
+Linux Kernel Integrity Module (LKIM).
+
+Trust Chains
+============
+
+Building upon the understanding of security mechanisms to establish load-time
+integrity of an entity, it is possible to chain together load-time integrity
+assessments to establish the integrity of the whole system. This process is
+known as transitive trust and provides the concept of building a chain of
+load-time integrity assessments, commonly referred to as a trust chain. These
+assessments may be used to adjudicate the load-time integrity of the whole
+system. This trust chain is started by a trusted entity that does the first
+assessment. This first entity is referred to as the Root of Trust(RoT) with the
+entities name being derived from the mechanism used for the assessment, i.e.
+RoT for Verification (RTV) and RoT for Measurement (RTM).
+
+A trust chain is itself a mechanism, specifically a mechanism of mechanisms,
+and therefore it too has a Strength of Mechanism. The factors that contribute
+to the strength of a trust chain are,
+
+ - The strength of the chain's RoT
+ - The strength of each member of the trust chain
+ - The length, i.e. the number of members, of the chain
+
+Therefore, to provide the strongest trust chains, they should start with a
+strong RoT and should consist of members being of low complexity and minimizing
+the number of members participating as possible. In a more colloquial sense, a
+trust chain is only as strong as its weakest link, thus more links increase the
+probability of a weak link.
+
+Dynamic Launch Components
+=========================
+
+The TCG architecture for dynamic launch is composed of a component series that
+are used to set up and then carry out the launch. These components work
+together to construct an RTM trust chain that is rooted in the dynamic launch
+and thus commonly referred to as the Dynamic Root of Trust for Measurement
+(DRTM) chain.
+
+What follows is a brief explanation of each component in execution order. A
+subset of these components are what establishes the dynamic launch's trust
+chain.
+
+Dynamic Configuration Environment Preamble
+------------------------------------------
+
+The Dynamic Configuration Environment (DCE) Preamble is responsible for setting
+up the system environment in preparation for a dynamic launch. The DCE Preamble
+is not a part of the DRTM trust chain.
+
+Dynamic Launch Event
+--------------------
+
+The dynamic launch event is the event, typically a CPU instruction, that
+triggers the system's dynamic launch mechanism to begin the launch. The dynamic
+launch mechanism is also the RoT for the DRTM trust chain.
+
+Dynamic Configuration Environment
+---------------------------------
+
+The dynamic launch mechanism may have resulted in a reset of a portion of the
+system. To bring the system back to an adequate state for system software, the
+dynamic launch will hand over control to the DCE. Prior to handing over this
+control, the dynamic launch, will measure the DCE. Once the DCE is complete it
+will proceed to measure and then execute the Dynamic Launch Measured
+Environment (DLME).
+
+Dynamic Launch Measured Environment
+-----------------------------------
+
+The DLME is the first system kernel to have control of the system, but may not
+be the last. Depending on the usage and configuration, the DLME may be the
+final/target operating system, or it may be a bootloader that will load the
+final/target operating system.
+
+Why DRTM
+========
+
+It is a fact that DRTM increases the load-time integrity of the system by
+providing a trust chain that has an immutable hardware RoT, uses a limited
+number of small, special purpose code to establish the trust chain that starts
+the target operating system. As mentioned in the Trust Chain section, these are
+the main three factors in driving up the strength of a trust chain. As has been
+seen with the BootHole exploit, which in fact did not affect the integrity of
+DRTM solutions, the sophistication of attacks targeting system launch is at an
+all-time high. There is no reason a system should not employ every integrity
+measure hardware makes available. This is the crux of a defense-in-depth
+approach to system security. In the past, the now closed SMI gap was often
+pointed to as invalidating DRTM, which in fact was nothing but a straw man
+argument. As has continued to be demonstrated, if/when SMM is corrupted it can
+always circumvent all load-time integrity, SRTM and DRTM, because it is a
+run-time integrity problem. Regardless, Intel and AMD have both deployed
+runtime integrity for SMI and SMM which is tied directly to DRTM such that this
+perceived deficiency is now non-existent, and the world is moving forward with
+an expectation that DRTM must be present.
+
+Glossary
+========
+
+.. glossary::
+ integrity
+ Guarding against improper information modification or destruction, and
+ includes ensuring information non-repudiation and authenticity.
+
+ - NIST CNSSI No. 4009 - https://www.cnss.gov/CNSS/issuances/Instructions.cfm
+
+ mechanism
+ A process or system that is used to produce a particular result.
+
+ - NIST Special Publication 800-160 (VOLUME 1 ) - https://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.800-160v1.pdf
+
+ risk
+ A measure of the extent to which an entity is threatened by a potential
+ circumstance or event, and typically a function of: (i) the adverse impacts
+ that would arise if the circumstance or event occurs; and (ii) the
+ likelihood of occurrence.
+
+ - NIST SP 800-30 Rev. 1 - https://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublication800-30r1.pdf
+
+ security mechanism
+ A device or function designed to provide one or more security services
+ usually rated in terms of strength of service and assurance of the design.
+
+ - NIST CNSSI No. 4009 - https://www.cnss.gov/CNSS/issuances/Instructions.cfm
+
+ Strength of Mechanism
+ A scale for measuring the relative strength of a security mechanism
+
+ - NIST CNSSI No. 4009 - https://www.cnss.gov/CNSS/issuances/Instructions.cfm
+
+ transitive trust
+ Also known as "Inductive Trust", in this process a Root of Trust gives a
+ trustworthy description of a second group of functions. Based on this
+ description, an interested entity can determine the trust it is to place in
+ this second group of functions. If the interested entity determines that
+ the trust level of the second group of functions is acceptable, the trust
+ boundary is extended from the Root of Trust to include the second group of
+ functions. In this case, the process can be iterated. The second group of
+ functions can give a trustworthy description of the third group of
+ functions, etc. Transitive trust is used to provide a trustworthy
+ description of platform characteristics, and also to prove that
+ non-migratable keys are in fact non-migratable.
+
+ - TCG Glossary - https://trustedcomputinggroup.org/wp-content/uploads/TCG-Glossary-V1.1-Rev-1.0.pdf
+
+ trust
+ The confidence one element has in another that the second element will
+ behave as expected`
+
+ - NISTIR 8320A - https://nvlpubs.nist.gov/nistpubs/ir/2021/NIST.IR.8320A.pdf
+
+ trust anchor
+ An authoritative entity for which trust is assumed.
+
+ - NIST SP 800-57 Part 1 Rev. 5 - https://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.800-57pt1r5.pdf
+
+ trusted
+ An element that another element relies upon to fulfill critical
+ requirements on its behalf.
+
+ - NISTIR 8320A - https://nvlpubs.nist.gov/nistpubs/ir/2021/NIST.IR.8320A.pdf
+
+ trusted computing base (TCB)
+ Totality of protection mechanisms within a computer system, including
+ hardware, firmware, and software, the combination responsible for enforcing
+ a security policy.
+
+ - NIST CNSSI No. 4009 - https://www.cnss.gov/CNSS/issuances/Instructions.cfm
+
+ trusted computer system
+ A system that has the necessary security functions and assurance that the
+ security policy will be enforced and that can process a range of
+ information sensitivities (i.e. classified, controlled unclassified
+ information (CUI), or unclassified public information) simultaneously.
+
+ - NIST CNSSI No. 4009 - https://www.cnss.gov/CNSS/issuances/Instructions.cfm
+
+ trustworthiness
+ The attribute of a person or enterprise that provides confidence to others
+ of the qualifications, capabilities, and reliability of that entity to
+ perform specific tasks and fulfill assigned responsibilities.
+
+ - NIST CNSSI No. 4009 - https://www.cnss.gov/CNSS/issuances/Instructions.cfm
diff --git a/Documentation/security/launch-integrity/secure_launch_details.rst b/Documentation/security/launch-integrity/secure_launch_details.rst
new file mode 100644
index 000000000000..7ea4cd1bdac9
--- /dev/null
+++ b/Documentation/security/launch-integrity/secure_launch_details.rst
@@ -0,0 +1,587 @@
+.. SPDX-License-Identifier: GPL-2.0
+.. Copyright © 2019-2024 Daniel P. Smith <dpsmith at apertussolutions.com>
+
+===================================
+Secure Launch Config and Interfaces
+===================================
+
+:Author: Daniel P. Smith
+:Date: August 2024
+
+Configuration
+=============
+
+The settings to enable Secure Launch using Kconfig are under::
+
+ "Processor type and features" --> "Secure Launch support"
+
+A kernel with this option enabled can still be booted using other supported
+methods.
+
+To reduce the Trusted Computing Base (TCB) of the MLE [1]_, the build
+configuration should be pared down as narrowly as one's use case allows. The
+fewer drivers (less active hardware) and features reduces the attack surface.
+As an example in the extreme, the MLE could only have local disk access with no
+other hardware supports, except optional network access for remote attestation.
+
+It is also desirable, if possible, to embed the initrd used with the MLE kernel
+image to reduce complexity.
+
+The following are a few important configuration necessities to always consider:
+
+KASLR Configuration
+-------------------
+
+Due to Secure Launch hardware implementation details and how KASLR functions,
+Secure Launch is not able to interoperate with KASLR at this time. Attempts to
+enable KASLR in a kernel started using Secure Launch may result in crashes and
+other instabilities at boot. Even in cases where Secure Launch and KASLR work
+together, it is still recommended that KASLR be disabled to avoid introducing
+security concerns with unprotected kernel memory.
+
+If possible, a kernel being used as an MLE should be built with KASLR disabled::
+
+ "Processor type and features" -->
+ "Build a relocatable kernel" -->
+ "Randomize the address of the kernel image (KASLR) [ ]"
+
+This action unsets the Kconfig value CONFIG_RANDOMIZE_BASE.
+
+If it is not possible to disable at build time, then it is recommended to force
+KASLR to be disabled using the kernel command line when doing a Secure Launch.
+The kernel parameter is as follows::
+
+ nokaslr
+
+.. note::
+ Should KASLR be made capable of reading/using only the protected page
+ regions set up by the memory protection mechanisms used by the hardware
+ DRTM capability, then it would become possible to use KASLR with Secure
+ Launch.
+
+IOMMU Configuration
+-------------------
+
+When doing a Secure Launch, the IOMMU should always be enabled and the drivers
+loaded. However, IOMMU passthrough mode should never be used. This leaves the
+MLE completely exposed to DMA after the PMR's [2]_ are disabled. The current
+default mode is to use IOMMU in lazy translated mode, but strict translated
+mode is the preferred IOMMU mode and this should be selected in the build
+configuration::
+
+ "Device Drivers" -->
+ "IOMMU Hardware Support" -->
+ "IOMMU default domain type" -->
+ "(X) Translated - Strict"
+
+In addition, the Intel IOMMU should be on by default. The following sets this as the
+default in the build configuration::
+
+ "Device Drivers" -->
+ "IOMMU Hardware Support" -->
+ "Support for Intel IOMMU using DMA Remapping Devices [*]"
+
+and::
+
+ "Device Drivers" -->
+ "IOMMU Hardware Support" -->
+ "Support for Intel IOMMU using DMA Remapping Devices [*]" -->
+ "Enable Intel DMA Remapping Devices by default [*]"
+
+It is recommended that no other command line options should be set to override
+the defaults above. If there is a desire to run an alternate configuration,
+then that configuration should be evaluated for what benefits are attempting to
+be gained against the risks for DMA attacks for which the kernel is likely
+going to be exposed.
+
+Secure Launch Resource Table
+============================
+
+The Secure Launch Resource Table (SLRT) is a platform-agnostic, standard format
+for providing information for the pre-launch environment and to pass
+information to the post-launch environment. The table is populated by one or
+more bootloaders in the boot chain and used by Secure Launch on how to set up
+the environment during post-launch. The details for the SLRT are documented
+in the TrenchBoot Secure Launch Specification [3]_.
+
+Intel TXT Interface
+===================
+
+The primary interfaces between the various components in TXT are the TXT MMIO
+registers and the TXT heap. The MMIO register banks are described in Appendix B
+of the TXT MLE [1]_ Development Guide.
+
+The TXT heap is described in Appendix C of the TXT MLE [1]_ Development
+Guide. Most of the TXT heap is predefined in the specification. The heap is
+initialized by firmware and the pre-launch environment and is subsequently used
+by the SINIT ACM. One section, called the OS to MLE Data Table, is reserved for
+software to define. This table is set up per the recommendation detailed in
+Appendix B of the TrenchBoot Secure Launch Specification::
+
+ /*
+ * Secure Launch defined OS/MLE TXT Heap table
+ */
+ struct txt_os_mle_data {
+ u32 version;
+ u32 boot_params_addr;
+ u64 slrt;
+ u64 txt_info;
+ u32 ap_wake_block;
+ u32 ap_wake_block_size;
+ u8 mle_scratch[64];
+ } __packed;
+
+Description of structure:
+
+===================== ========================================================================
+Field Use
+===================== ========================================================================
+version Structure version, current value 1
+boot_params_addr Physical base address of the Linux boot parameters
+slrt Physical address of the Secure Launch Resource Table
+txt_info Pointer into the SLRT for easily locating TXT specific table
+ap_wake_block Physical address of the block of memory for parking APs after a launch
+ap_wake_block_size Size of the AP wake block
+mle_scratch Scratch area used post-launch by the MLE kernel. Fields:
+
+ - SL_SCRATCH_AP_EBX area to share %ebx base pointer among CPUs
+ - SL_SCRATCH_AP_JMP_OFFSET offset to abs. ljmp fixup location for APs
+===================== ========================================================================
+
+Error Codes
+-----------
+
+The TXT specification defines the layout for TXT 32 bit error code values.
+The bit encodings indicate where the error originated (e.g. with the CPU,
+in the SINIT ACM, in software). The error is written to a sticky TXT
+register that persists across resets called TXT.ERRORCODE (see the TXT
+MLE Development Guide). The errors defined by the Secure Launch feature are
+those generated in the MLE software. They have the format::
+
+ 0xc0008XXX
+
+The low 12 bits are free for defining the following Secure Launch specific
+error codes.
+
+====== ================
+Name: SL_ERROR_GENERIC
+Value: 0xc0008001
+====== ================
+
+Description:
+
+Generic catch all error. Currently unused.
+
+====== =================
+Name: SL_ERROR_TPM_INIT
+Value: 0xc0008002
+====== =================
+
+Description:
+
+The Secure Launch code failed to get access to the TPM hardware interface.
+This is most likely due to misconfigured hardware or kernel. Ensure the TPM
+chip is enabled, and the kernel TPM support is built in (it should not be built
+as a module).
+
+====== ==========================
+Name: SL_ERROR_TPM_INVALID_LOG20
+Value: 0xc0008003
+====== ==========================
+
+Description:
+
+The Secure Launch code failed to find a valid event log descriptor for a
+version 2.0 TPM or the event log descriptor is malformed. Usually this
+indicates there are incompatible versions of the pre-launch environment and the
+MLE kernel. The pre-launch environment and the kernel share a structure in the
+TXT heap and if this structure (the OS-MLE table) is mismatched, this error is
+often seen. This TXT heap area is set up by the pre-launch environment, so the
+issue may originate there. It could also be the sign of an attempted attack.
+
+====== ===========================
+Name: SL_ERROR_TPM_LOGGING_FAILED
+Value: 0xc0008004
+====== ===========================
+
+Description:
+
+There was a failed attempt to write a TPM event to the event log early in the
+Secure Launch process. This is likely the result of a malformed TPM event log
+buffer. Formatting of the event log buffer information is done by the
+pre-launch environment, so the issue most likely originates there.
+
+====== ============================
+Name: SL_ERROR_REGION_STRADDLE_4GB
+Value: 0xc0008005
+====== ============================
+
+Description:
+
+During early validation, a buffer or region was found to straddle the 4GB
+boundary. Because of the way TXT does DMA memory protection, this is an unsafe
+configuration and is flagged as an error. This is most likely a configuration
+issue in the pre-launch environment. It could also be the sign of an attempted
+attack.
+
+====== ===================
+Name: SL_ERROR_TPM_EXTEND
+Value: 0xc0008006
+====== ===================
+
+Description:
+
+There was a failed attempt to extend a TPM PCR in the Secure Launch platform
+module. This is most likely to due to misconfigured hardware or kernel. Ensure
+the TPM chip is enabled, and the kernel TPM support is built in (it should not
+be built as a module).
+
+====== ======================
+Name: SL_ERROR_MTRR_INV_VCNT
+Value: 0xc0008007
+====== ======================
+
+Description:
+
+During early Secure Launch validation, an invalid variable MTRR count was
+found. The pre-launch environment passes a number of MSR values to the MLE to
+restore including the MTRRs. The values are restored by the Secure Launch early
+entry point code. After measuring the values supplied by the pre-launch
+environment, a discrepancy was found, validating the values. It could be the
+sign of an attempted attack.
+
+====== ==========================
+Name: SL_ERROR_MTRR_INV_DEF_TYPE
+Value: 0xc0008008
+====== ==========================
+
+Description:
+
+During early Secure Launch validation, an invalid default MTRR type was found.
+See SL_ERROR_MTRR_INV_VCNT for more details.
+
+====== ======================
+Name: SL_ERROR_MTRR_INV_BASE
+Value: 0xc0008009
+====== ======================
+
+Description:
+
+During early Secure Launch validation, an invalid variable MTRR base value was
+found. See SL_ERROR_MTRR_INV_VCNT for more details.
+
+====== ======================
+Name: SL_ERROR_MTRR_INV_MASK
+Value: 0xc000800a
+====== ======================
+
+Description:
+
+During early Secure Launch validation, an invalid variable MTRR mask value was
+found. See SL_ERROR_MTRR_INV_VCNT for more details.
+
+====== ========================
+Name: SL_ERROR_MSR_INV_MISC_EN
+Value: 0xc000800b
+====== ========================
+
+Description:
+
+During early Secure Launch validation, an invalid miscellaneous enable MSR
+value was found. See SL_ERROR_MTRR_INV_VCNT for more details.
+
+====== =========================
+Name: SL_ERROR_INV_AP_INTERRUPT
+Value: 0xc000800c
+====== =========================
+
+Description:
+
+The application processors (APs) wait to be woken up by the SMP initialization
+code. The only interrupt that they expect is an NMI; all other interrupts
+should be masked. If an AP gets some other interrupt other than an NMI, it will
+cause this error. This error is very unlikely to occur.
+
+====== =========================
+Name: SL_ERROR_INTEGER_OVERFLOW
+Value: 0xc000800d
+====== =========================
+
+Description:
+
+A buffer base and size passed to the MLE caused an integer overflow when
+added together. This is most likely a configuration issue in the pre-launch
+environment. It could also be the sign of an attempted attack.
+
+====== ==================
+Name: SL_ERROR_HEAP_WALK
+Value: 0xc000800e
+====== ==================
+
+Description:
+
+An error occurred in TXT heap walking code. The underlying issue is a failure to
+early_memremap() portions of the heap, most likely due to a resource shortage.
+
+====== =================
+Name: SL_ERROR_HEAP_MAP
+Value: 0xc000800f
+====== =================
+
+Description:
+
+This error is essentially the same as SL_ERROR_HEAP_WALK but occurred during the
+actual early_memremap() operation.
+
+====== =========================
+Name: SL_ERROR_REGION_ABOVE_4GB
+Value: 0xc0008010
+====== =========================
+
+Description:
+
+A memory region used by the MLE is above 4GB. In general this is not a problem
+because memory > 4Gb can be protected from DMA. There are certain buffers that
+should never be above 4Gb, and one of these caused the violation. This is most
+likely a configuration issue in the pre-launch environment. It could also be
+the sign of an attempted attack.
+
+====== ==========================
+Name: SL_ERROR_HEAP_INVALID_DMAR
+Value: 0xc0008011
+====== ==========================
+
+Description:
+
+The backup copy of the ACPI DMAR table which is supposed to be located in the
+TXT heap could not be found. This is due to a bug in the platform's ACM module
+or in firmware.
+
+====== =======================
+Name: SL_ERROR_HEAP_DMAR_SIZE
+Value: 0xc0008012
+====== =======================
+
+Description:
+
+The backup copy of the ACPI DMAR table in the TXT heap is to large to be stored
+for later usage. This error is very unlikely to occur since the area reserved
+for the copy is far larger than the DMAR should be.
+
+====== ======================
+Name: SL_ERROR_HEAP_DMAR_MAP
+Value: 0xc0008013
+====== ======================
+
+Description:
+
+The backup copy of the ACPI DMAR table in the TXT heap could not be mapped. The
+underlying issue is a failure to early_memremap() the DMAR table, most likely
+due to a resource shortage.
+
+====== ====================
+Name: SL_ERROR_HI_PMR_BASE
+Value: 0xc0008014
+====== ====================
+
+Description:
+
+On a system with more than 4G of RAM, the high PMR [2]_ base address should be
+set to 4G. This error is due to that not being the case. This PMR value is set
+by the pre-launch environment, so the issue most likely originates there. It
+could also be the sign of an attempted attack.
+
+====== ====================
+Name: SL_ERROR_HI_PMR_SIZE
+Value: 0xc0008015
+====== ====================
+
+Description:
+
+On a system with more than 4G of RAM, the high PMR [2]_ size should be set to
+cover all RAM > 4G. This error is due to that not being the case. This PMR
+value is set by the pre-launch environment, so the issue most likely originates
+there. It could also be the sign of an attempted attack.
+
+====== ====================
+Name: SL_ERROR_LO_PMR_BASE
+Value: 0xc0008016
+====== ====================
+
+Description:
+
+The low PMR [2]_ base should always be set to address zero. This error is due
+to that not being the case. This PMR value is set by the pre-launch environment
+so the issue most likely originates there. It could also be the sign of an
+attempted attack.
+
+====== ====================
+Name: SL_ERROR_LO_PMR_MLE
+Value: 0xc0008017
+====== ====================
+
+Description:
+
+This error indicates the MLE image is not covered by the low PMR [2]_ range.
+The PMR values are set by the pre-launch environment, so the issue most likely
+originates there. It could also be the sign of an attempted attack.
+
+====== =======================
+Name: SL_ERROR_INITRD_TOO_BIG
+Value: 0xc0008018
+====== =======================
+
+Description:
+
+The external initrd provided is larger than 4Gb. This is not a valid
+configuration for a Secure Launch due to managing DMA protection.
+
+====== =========================
+Name: SL_ERROR_HEAP_ZERO_OFFSET
+Value: 0xc0008019
+====== =========================
+
+Description:
+
+During a TXT heap walk, an invalid/zero next table offset value was found. This
+indicates the TXT heap is malformed. The TXT heap is initialized by the
+pre-launch environment, so the issue most likely originates there. It could
+also be a sign of an attempted attack. In addition, ACM is also responsible for
+manipulating parts of the TXT heap, so the issue could be due to a bug in the
+platform's ACM module.
+
+====== =============================
+Name: SL_ERROR_WAKE_BLOCK_TOO_SMALL
+Value: 0xc000801a
+====== =============================
+
+Description:
+
+The AP wake block buffer passed to the MLE via the OS-MLE TXT heap table is not
+large enough. This value is set by the pre-launch environment, so the issue
+most likely originates there. It also could be the sign of an attempted attack.
+
+====== ===========================
+Name: SL_ERROR_MLE_BUFFER_OVERLAP
+Value: 0xc000801b
+====== ===========================
+
+Description:
+
+One of the buffers passed to the MLE via the OS-MLE TXT heap table overlaps
+with the MLE image in memory. This value is set by the pre-launch environment
+so the issue most likely originates there. It could also be the sign of an
+attempted attack.
+
+====== ==========================
+Name: SL_ERROR_BUFFER_BEYOND_PMR
+Value: 0xc000801c
+====== ==========================
+
+Description:
+
+One of the buffers passed to the MLE via the OS-MLE TXT heap table is not
+protected by a PMR. This value is set by the pre-launch environment, so the
+issue most likely originates there. It could also be the sign of an attempted
+attack.
+
+====== =============================
+Name: SL_ERROR_OS_SINIT_BAD_VERSION
+Value: 0xc000801d
+====== =============================
+
+Description:
+
+The version of the OS-SINIT TXT heap table is bad. It must be 6 or greater.
+This value is set by the pre-launch environment, so the issue most likely
+originates there. It could also be the sign of an attempted attack. It is also
+possible though very unlikely that the platform is so old that the ACM being
+used requires an unsupported version.
+
+====== =====================
+Name: SL_ERROR_EVENTLOG_MAP
+Value: 0xc000801e
+====== =====================
+
+Description:
+
+An error occurred in the Secure Launch module while mapping the TPM event log.
+The underlying issue is memremap() failure, most likely due to a resource
+shortage.
+
+====== ========================
+Name: SL_ERROR_TPM_NUMBER_ALGS
+Value: 0xc000801f
+====== ========================
+
+Description:
+
+The TPM 2.0 event log reports an unsupported number of hashing algorithms.
+Secure launch currently only supports a maximum of two: SHA1 and SHA256.
+
+====== ===========================
+Name: SL_ERROR_TPM_UNKNOWN_DIGEST
+Value: 0xc0008020
+====== ===========================
+
+Description:
+
+The TPM 2.0 event log reports an unsupported hashing algorithm. Secure launch
+currently only supports two algorithms: SHA1 and SHA256.
+
+====== ==========================
+Name: SL_ERROR_TPM_INVALID_EVENT
+Value: 0xc0008021
+====== ==========================
+
+Description:
+
+An invalid/malformed event was found in the TPM event log while reading it.
+Since only trusted entities are supposed to be writing the event log, this
+would indicate either a bug or a possible attack.
+
+====== =====================
+Name: SL_ERROR_INVALID_SLRT
+Value: 0xc0008022
+====== =====================
+
+Description:
+
+The Secure Launch Resource Table is invalid or malformed and is unusable. This
+implies the pre-launch code did not properly set up the SLRT.
+
+====== ===========================
+Name: SL_ERROR_SLRT_MISSING_ENTRY
+Value: 0xc0008023
+====== ===========================
+
+Description:
+
+The Secure Launch Resource Table is missing a required entry within it. This
+implies the pre-launch code did not properly set up the SLRT.
+
+====== =================
+Name: SL_ERROR_SLRT_MAP
+Value: 0xc0008024
+====== =================
+
+Description:
+
+An error occurred in the Secure Launch module while mapping the Secure Launch
+Resource table. The underlying issue is memremap() failure, most likely due to
+a resource shortage.
+
+.. [1]
+ MLE: Measured Launch Environment is the binary runtime that is measured and
+ then run by the TXT SINIT ACM. The TXT MLE Development Guide describes the
+ requirements for the MLE in detail.
+
+.. [2]
+ PMR: Intel VTd has a feature in the IOMMU called Protected Memory Registers.
+ There are two of these registers and they allow all DMA to be blocked
+ to large areas of memory. The low PMR can cover all memory below 4Gb on 2Mb
+ boundaries. The high PMR can cover all RAM on the system, again on 2Mb
+ boundaries. This feature is used during a Secure Launch by TXT.
+
+.. [3]
+ Secure Launch Specification: https://trenchboot.org/specifications/Secure_Launch/
diff --git a/Documentation/security/launch-integrity/secure_launch_overview.rst b/Documentation/security/launch-integrity/secure_launch_overview.rst
new file mode 100644
index 000000000000..47e2e8ede88d
--- /dev/null
+++ b/Documentation/security/launch-integrity/secure_launch_overview.rst
@@ -0,0 +1,227 @@
+.. SPDX-License-Identifier: GPL-2.0
+.. Copyright © 2019-2024 Daniel P. Smith <dpsmith at apertussolutions.com>
+
+======================
+Secure Launch Overview
+======================
+
+:Author: Daniel P. Smith
+:Date: August 2024
+
+Overview
+========
+
+Prior to the start of the TrenchBoot project, the only active Open Source
+project supporting dynamic launch was Intel's tboot project to support their
+implementation of dynamic launch known as Intel Trusted eXecution Technology
+(TXT). The approach taken by tboot was to provide an exokernel that could
+handle the launch protocol implemented by Intel's special loader, the SINIT
+Authenticated Code Module (ACM [2]_) and remained in memory to manage the SMX
+CPU mode that a dynamic launch would put a system. While it is not precluded
+from being used for doing a late launch, tboot's primary use case was to be
+used as an early launch solution. As a result, the TrenchBoot project started
+the development of Secure Launch kernel feature to provide a more generalized
+approach. The focus of the effort is twofold, the first is to make the Linux
+kernel directly aware of the launch protocol used by Intel, AMD/Hygon, Arm, and
+potentially OpenPOWER. The second is to make the Linux kernel be able to
+initiate a dynamic launch. It is through this approach that the Secure Launch
+kernel feature creates a basis for the Linux kernel to be used in a variety of
+dynamic launch use cases.
+
+.. note::
+ A quick note on terminology. The larger open source project itself is
+ called TrenchBoot, which is hosted on GitHub (links below). The kernel
+ feature enabling the use of the x86 technology is referred to as "Secure
+ Launch" within the kernel code.
+
+Goals
+=====
+
+The first use case that the TrenchBoot project focused on was the ability for
+the Linux kernel to be started by a dynamic launch, in particular as part of an
+early launch sequence. In this case, the dynamic launch will be initiated by
+any bootloader with associated support added to it, for example the first
+targeted bootloader in this case was GRUB2. An integral part of establishing a
+measurement-based launch integrity involves measuring everything that is
+intended to be executed (kernel image, initrd, etc.) and everything that will
+configure that kernel to execute (command line, boot params, etc.). Then
+storing those measurements in a protected manner. Both the Intel and AMD
+dynamic launch implementations leverage the Trusted Platform Module (TPM) to
+store those measurements. The TPM itself has been designed such that a dynamic
+launch unlocks a specific set of Platform Configuration Registers (PCR) for
+holding measurement taken during the dynamic launch. These are referred to as
+the DRTM PCRs, PCRs 17-22. Further details on this process can be found in the
+documentation for the GETSEC instruction provided by Intel's TXT and the SKINIT
+instruction provided by AMD's AMD-V. The documentation on these technologies
+can be readily found online; see the `Resources`_ section below for references.
+
+.. note::
+ Currently, only Intel TXT is supported in this first release of the Secure
+ Launch feature. AMD/Hygon SKINIT and Arm support will be added in a
+ subsequent release.
+
+To enable the kernel to be launched by GETSEC a stub, the Secure Launch stub,
+must be built into the setup section of the compressed kernel to handle the
+specific state that the dynamic launch process leaves the BSP. Also, the Secure
+Launch stub must measure everything that is going to be used as early as
+possible. This stub code and subsequent code must also deal with the specific
+state that the dynamic launch leaves the APs as well.
+
+Design Decisions
+================
+
+A number of design decisions were made during the development of the Secure
+Launch feature. The two primary guiding decisions were:
+
+ - Keeping the Secure Launch code as separate from the rest of the kernel
+ as possible.
+ - Modifying the existing boot path of the kernel as little as possible.
+
+The following illustrate how the implementation followed these design
+decisions:
+
+ - All the entry point code necessary to properly configure the system post
+ launch is found in st_stub.S in the compressed kernel image. This code
+ validates the state of the system, restores necessary system operating
+ configurations and properly handles post launch CPU states.
+ - After the sl_stub.S is complete, it jumps directly to the unmodified
+ startup_32 kernel entry point.
+ - A single call is made to a function sl_main() prior to the main kernel
+ decompression step. This code performs further validation and takes the
+ needed DRTM measurements.
+ - After the call to sl_main(), the main kernel is decompressed and boots as
+ it normally would.
+ - Final setup for the Secure Launch kernel is done in a separate Secure
+ Launch module that is loaded via a late initcall. This code is responsible
+ for extending the measurements taken earlier into the TPM DRTM PCRs and
+ setting up the securityfs interface to allow access to the TPM event log and
+ public TXT registers.
+ - On the reboot and kexec paths, calls are made to a function to finalize the
+ state of the Secure Launch kernel.
+
+The one place where Secure Launch code is mixed directly in with kernel code is
+in the SMP boot code. This is due to the unique state that the dynamic launch
+leaves the APs in. On Intel, this involves using a method other than the
+standard INIT-SIPI sequence.
+
+A final note is that originally the extending of the PCRs was completed in the
+Secure Launch stub when the measurements were taken. An alternative solution
+had to be implemented due to the TPM maintainers objecting to the PCR
+extensions being done with a minimal interface to the TPM that was an
+independent implementation of the mainline kernel driver. Since the mainline
+driver relies heavily on kernel interfaces not available in the compressed
+kernel, it was not possible to reuse the mainline TPM driver. This resulted in
+the decision to move the extension operations to the Secure Launch module in
+the mainline kernel, where the TPM driver would be available.
+
+Basic Boot Flow
+===============
+
+Outlined here is a summary of the boot flow for Secure Launch. A more detailed
+review of Secure Launch process can be found in the Secure Launch
+Specification, a link is located in the `Resources`_ section.
+
+Pre-launch: *Phase where the environment is prepared and configured to initiate
+the secure launch by the boot chain.*
+
+ - The SLRT is initialized and dl_stub is placed in memory.
+ - Load the kernel, initrd and ACM [2]_ into memory.
+ - Set up the TXT heap and page tables describing the MLE [1]_ per the
+ specification.
+ - If non-UEFI platform, dl_stub is called.
+ - If UEFI platforms, SLRT registered with UEFI and efi-stub called.
+ - Upon completion, efi-stub will call EBS followed by dl_stub.
+ - The dl_stub will prepare the CPU and the TPM for the launch.
+ - The secure launch is then initiated with the GETSET[SENTER] instruction.
+
+Post-launch: *Phase where control is passed from the ACM to the MLE and the secure
+kernel begins execution.*
+
+ - Entry from the dynamic launch jumps to the SL stub.
+ - SL stub fixes up the world on the BSP.
+ - For TXT, SL stub wakes the APs, fixes up their worlds.
+ - For TXT, APs are left halted using MONITOR/MWAIT intructions.
+ - SL stub jumps to startup_32.
+ - SL main does validation of buffers and memory locations. It sets
+ the boot parameter loadflag value SLAUNCH_FLAG to inform the main
+ kernel that a Secure Launch was done.
+ - SL main locates the TPM event log and writes the measurements of
+ configuration and module information into it.
+ - Kernel boot proceeds normally from this point.
+ - During early setup, slaunch_setup() runs to finish some validation
+ and setup tasks.
+ - The SMP bring up code is modified to wake the waiting APs via the monitor
+ address.
+ - APs vector to rmpiggy and start up normally from that point.
+ - SL platform module is registered as a late initcall module. It reads
+ the TPM event log and extends the measurements taken into the TPM PCRs.
+ - SL platform module initializes the securityfs interface to allow
+ access to the TPM event log and TXT public registers.
+ - Kernel boot finishes booting normally
+ - SEXIT support to leave SMX mode is present on the kexec path and
+ the various reboot paths (poweroff, reset, halt).
+
+PCR Usage
+=========
+
+The TCG DRTM architecture there are three PCRs defined for usage, PCR.Details
+(PCR17), PCR.Authorities (PCR18), and PCR.DLME_Authority (PCR19). For a deeper
+understanding of Detail and Authorities it is recommended to review the TCG
+DRTM architecture.
+
+To determine PCR usage, Linux Secure Launch follows the TrenchBoot Secure
+Launch Specification of using a measurement policy stored in the SLRT. The
+policy details what should be measured and the PCR in which to store the
+measurement. The measurement policy provides the ability to select the
+PCR.DLME_Detail (PCR20) PCR as the location for the DRTM components measured by
+the kernel, e.g. external initrd image. This can then be combined with storing
+the user authority in the PCR.DLME_Authority PCR to seal/attest to different
+variations of platform details/authorities and user details/authorities. An
+example of how this can be achieved was presented in the FOSDEM - 2021 talk
+"Secure Upgrades with DRTM".
+
+Resources
+=========
+
+The TrenchBoot project:
+
+https://trenchboot.org
+
+Secure Launch Specification:
+
+https://trenchboot.org/specifications/Secure_Launch/
+
+Trusted Computing Group's D-RTM Architecture:
+
+https://trustedcomputinggroup.org/wp-content/uploads/TCG_D-RTM_Architecture_v1-0_Published_06172013.pdf
+
+TXT documentation in the Intel TXT MLE Development Guide:
+
+https://www.intel.com/content/dam/www/public/us/en/documents/guides/intel-txt-software-development-guide.pdf
+
+TXT instructions documentation in the Intel SDM Instruction Set volume:
+
+https://software.intel.com/en-us/articles/intel-sdm
+
+AMD SKINIT documentation in the System Programming manual:
+
+https://www.amd.com/system/files/TechDocs/24593.pdf
+
+GRUB Secure Launch support:
+
+https://github.com/TrenchBoot/grub/tree/grub-sl-fc-38-dlstub
+
+FOSDEM 2021: Secure Upgrades with DRTM
+
+https://archive.fosdem.org/2021/schedule/event/firmware_suwd/
+
+.. [1]
+ MLE: Measured Launch Environment is the binary runtime that is measured and
+ then run by the TXT SINIT ACM. The TXT MLE Development Guide describes the
+ requirements for the MLE in detail.
+
+.. [2]
+ ACM: Intel's Authenticated Code Module. This is the 32b bit binary blob that
+ is run securely by the GETSEC[SENTER] during a measured launch. It is described
+ in the Intel documentation on TXT and versions for various chipsets are
+ signed and distributed by Intel.
--
2.39.3
More information about the kexec
mailing list