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Date: Wed, 10 May 2023 11:41:37 -0400
From: Ross Philipson <ross.philipson@...cle.com>
To: Bagas Sanjaya <bagasdotme@...il.com>, linux-kernel@...r.kernel.org,
x86@...nel.org, linux-integrity@...r.kernel.org,
linux-doc@...r.kernel.org, linux-crypto@...r.kernel.org,
kexec@...ts.infradead.org, linux-efi@...r.kernel.org,
iommu@...ts.linux.dev
Cc: dpsmith@...rtussolutions.com, tglx@...utronix.de, mingo@...hat.com,
bp@...en8.de, hpa@...or.com, ardb@...nel.org, mjg59@...f.ucam.org,
James.Bottomley@...senpartnership.com, luto@...capital.net,
nivedita@...m.mit.edu, kanth.ghatraju@...cle.com,
trenchboot-devel@...glegroups.com
Subject: Re: [PATCH v6 02/14] Documentation/x86: Secure Launch kernel
documentation
On 5/6/23 04:48, Bagas Sanjaya wrote:
> 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.
Will do.
>
>> 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@...il.com>
Thank you,
Ross
>
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