[PATCH v6 02/14] Documentation/x86: Secure Launch kernel documentation
Bagas Sanjaya
bagasdotme at gmail.com
Sat May 6 01:48:41 PDT 2023
On Thu, May 04, 2023 at 02:50:11PM +0000, Ross Philipson wrote:
> +=====================================
> +System Launch Integrity documentation
> +=====================================
> +
> +.. toctree::
By convention, doc toctree have 2-level depth (only page title and
first-level headings are visible). You may consider adding
`:maxdepth: 2` option.
> diff --git a/Documentation/security/launch-integrity/principles.rst b/Documentation/security/launch-integrity/principles.rst
> new file mode 100644
> index 0000000..73cf063
> --- /dev/null
> +++ b/Documentation/security/launch-integrity/principles.rst
> @@ -0,0 +1,313 @@
> +=======================
> +System Launch Integrity
> +=======================
> +
> +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. Through out this document
> +terminology from the Trusted Computing Group (TCG) and National Institue for
> +Science and Technology (NIST) is used to ensure a vendor nutrual 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
> +is able to be implemented as 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 John Hopkins Advanced Physics Labratory's (APL)
> +Linux Kernel Integrity Module (LKIM).
> +
> +Trust Chains
> +============
> +
> +Bulding 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 a trust chain's strength 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 is possible. In a more colloquial sense,
> +a trust chain is only as strong as it weakests link and 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 setup and then carry out the launch. These components work together
> +to construct a 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 boot loader 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 can been
> +seen by the BootHole exploit, which in fact did not effect 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 strawman
> +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 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 0000000..2e71543
> --- /dev/null
> +++ b/Documentation/security/launch-integrity/secure_launch_details.rst
> @@ -0,0 +1,564 @@
> +===================================
> +Secure Launch Config and Interfaces
> +===================================
> +
> +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. E.g. in the extreme, the MLE could only have local disk access
> +and no other hardware support. Or only 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
> +-------------------
> +
> +Secure Launch does not interoperate with KASLR. If possible, the MLE should be
> +built with KASLR disabled::
> +
> + "Processor type and features" -->
> + "Build a relocatable kernel" -->
> + "Randomize the address of the kernel image (KASLR) [ ]"
> +
> +This unsets the Kconfig value CONFIG_RANDOMIZE_BASE.
> +
> +If not possible, KASLR must be disabled on the kernel command line when doing
> +a Secure Launch as follows::
> +
> + nokaslr
> +
> +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.
> +
> +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 setup
> +the environment during post-launch. The details for the SLRT are documented
> +in the TrenchBoot Secure Launch Specifcation [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;
> + struct slr_table *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 an access to the TPM hardware interface.
> +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_TPM_INVALID_LOG20
> +Value: 0xc0008003
> +====== ==========================
> +
> +Description:
> +
> +The Secure Launch code failed to find a valid event log descriptor for TPM
> +version 2.0 or the event log descriptor is malformed. Usually this indicates
> +that 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 setup by the pre-launch environment so the issue may
> +originate there. It could 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 though 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 likey 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 setup 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 setup 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 0000000..ba91d73
> --- /dev/null
> +++ b/Documentation/security/launch-integrity/secure_launch_overview.rst
> @@ -0,0 +1,220 @@
> +======================
> +Secure Launch Overview
> +======================
> +
> +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
> +boot loader with associated support added to it, for example the first targeted
> +boot loader 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 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 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.
> + - Setup 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 waiting for an NMI to wake them.
> + - 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. 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.
The formatting LGTM, thanks!
Regardless,
Reviewed-by: Bagas Sanjaya <bagasdotme at gmail.com>
--
An old man doll... just what I always wanted! - Clara
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