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Wed, 14 Feb 2024 22:31:32 GMT Received: from pps.reinject (localhost [127.0.0.1]) by iadpaimrmta02.imrmtpd1.prodappiadaev1.oraclevcn.com (PPS) with ESMTPS id 3w5yk9n75t-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO); Wed, 14 Feb 2024 22:31:32 +0000 Received: from iadpaimrmta02.imrmtpd1.prodappiadaev1.oraclevcn.com (iadpaimrmta02.imrmtpd1.prodappiadaev1.oraclevcn.com [127.0.0.1]) by pps.reinject (8.17.1.5/8.17.1.5) with ESMTP id 41EMVTUw004281; Wed, 14 Feb 2024 22:31:31 GMT Received: from bur-virt-x6-2-100.us.oracle.com (bur-virt-x6-2-100.us.oracle.com [10.153.92.40]) by iadpaimrmta02.imrmtpd1.prodappiadaev1.oraclevcn.com (PPS) with ESMTPS id 3w5yk9n72r-3 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NO); Wed, 14 Feb 2024 22:31:31 +0000 From: Ross Philipson To: linux-kernel@vger.kernel.org, x86@kernel.org, linux-integrity@vger.kernel.org, linux-doc@vger.kernel.org, linux-crypto@vger.kernel.org, kexec@lists.infradead.org, linux-efi@vger.kernel.org Cc: ross.philipson@oracle.com, dpsmith@apertussolutions.com, tglx@linutronix.de, mingo@redhat.com, bp@alien8.de, hpa@zytor.com, dave.hansen@linux.intel.com, ardb@kernel.org, mjg59@srcf.ucam.org, James.Bottomley@hansenpartnership.com, peterhuewe@gmx.de, jarkko@kernel.org, jgg@ziepe.ca, luto@amacapital.net, nivedita@alum.mit.edu, herbert@gondor.apana.org.au, davem@davemloft.net, kanth.ghatraju@oracle.com, trenchboot-devel@googlegroups.com Subject: [PATCH v8 02/15] Documentation/x86: Secure Launch kernel documentation Date: Wed, 14 Feb 2024 14:18:34 -0800 Message-Id: <20240214221847.2066632-3-ross.philipson@oracle.com> X-Mailer: git-send-email 2.39.3 In-Reply-To: <20240214221847.2066632-1-ross.philipson@oracle.com> References: <20240214221847.2066632-1-ross.philipson@oracle.com> Precedence: bulk X-Mailing-List: linux-crypto@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-Proofpoint-Virus-Version: vendor=baseguard engine=ICAP:2.0.272,Aquarius:18.0.1011,Hydra:6.0.619,FMLib:17.11.176.26 definitions=2024-02-14_14,2024-02-14_01,2023-05-22_02 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 mlxlogscore=999 phishscore=0 mlxscore=0 bulkscore=0 spamscore=0 malwarescore=0 adultscore=0 suspectscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2311290000 definitions=main-2402140170 X-Proofpoint-GUID: 0T7nD3ez8LGIBa78lTBm-ea1FgE4E1BT X-Proofpoint-ORIG-GUID: 0T7nD3ez8LGIBa78lTBm-ea1FgE4E1BT Introduce background, overview and configuration/ABI information for the Secure Launch kernel feature. Signed-off-by: Daniel P. Smith Signed-off-by: Ross Philipson Reviewed-by: Bagas Sanjaya --- Documentation/security/index.rst | 1 + .../security/launch-integrity/index.rst | 11 + .../security/launch-integrity/principles.rst | 320 ++++++++++ .../secure_launch_details.rst | 584 ++++++++++++++++++ .../secure_launch_overview.rst | 226 +++++++ 5 files changed, 1142 insertions(+) create mode 100644 Documentation/security/launch-integrity/index.rst create mode 100644 Documentation/security/launch-integrity/principles.rst create mode 100644 Documentation/security/launch-integrity/secure_launch_details.rst create mode 100644 Documentation/security/launch-integrity/secure_launch_overview.rst diff --git a/Documentation/security/index.rst b/Documentation/security/index.rst index 59f8fc106cb0..56e31fb3d91f 100644 --- a/Documentation/security/index.rst +++ b/Documentation/security/index.rst @@ -19,3 +19,4 @@ Security Documentation digsig landlock secrets/index + launch-integrity/index diff --git a/Documentation/security/launch-integrity/index.rst b/Documentation/security/launch-integrity/index.rst new file mode 100644 index 000000000000..838328186dd2 --- /dev/null +++ b/Documentation/security/launch-integrity/index.rst @@ -0,0 +1,11 @@ +===================================== +System Launch Integrity documentation +===================================== + +.. toctree:: + :maxdepth: 1 + + principles + secure_launch_overview + secure_launch_details + diff --git a/Documentation/security/launch-integrity/principles.rst b/Documentation/security/launch-integrity/principles.rst new file mode 100644 index 000000000000..68a415aec545 --- /dev/null +++ b/Documentation/security/launch-integrity/principles.rst @@ -0,0 +1,320 @@ +.. SPDX-License-Identifier: GPL-2.0 +.. Copyright © 2019-2023 Daniel P. Smith + +======================= +System Launch Integrity +======================= + +:Author: Daniel P. Smith +:Date: October 2023 + +This document serves to establish a common understanding of what is system +launch, the integrity concern for system launch, and why using a Root of Trust +(RoT) from a Dynamic Launch may be desired. Throughout this document +terminology from the Trusted Computing Group (TCG) and National Institute for +Science and Technology (NIST) is used to ensure a vendor natural language is +used to describe and reference security-related concepts. + +System Launch +============= + +There is a tendency to only consider the classical power-on boot as the only +means to launch an Operating System (OS) on a computer system, but in fact most +modern processors support two methods to launch the system. To provide clarity +a common definition of a system launch should be established. This definition +is that a during a single power life cycle of a system, a System Launch +consists of an initialization event, typically in hardware, that is followed by +an executing software payload that takes the system from the initialized state +to a running state. Driven by the Trusted Computing Group (TCG) architecture, +modern processors are able to support two methods to launch a system, these two +types of system launch are known as Static Launch and Dynamic Launch. + +Static Launch +------------- + +Static launch is the system launch associated with the power cycle of the CPU. +Thus, static launch refers to the classical power-on boot where the +initialization event is the release of the CPU from reset and the system +firmware is the software payload that brings the system up to a running state. +Since static launch is the system launch associated with the beginning of the +power lifecycle of a system, it is therefore a fixed, one-time system launch. +It is because of this that static launch is referred to and thought of as being +"static". + +Dynamic Launch +-------------- + +Modern CPUs architectures provides a mechanism to re-initialize the system to a +"known good" state without requiring a power event. This re-initialization +event is the event for a dynamic launch and is referred to as the Dynamic +Launch Event (DLE). The DLE functions by accepting a software payload, referred +to as the Dynamic Configuration Environment (DCE), that execution is handed to +after the DLE is invoked. The DCE is responsible for bringing the system back +to a running state. Since the dynamic launch is not tied to a power event like +the static launch, this enables a dynamic launch to be initiated at any time +and multiple times during a single power life cycle. This dynamism is the +reasoning behind referring to this system launch as being dynamic. + +Because a dynamic launch can be conducted at any time during a single power +life cycle, they are classified into one of two types, an early launch or a +late launch. + +:Early Launch: When a dynamic launch is used as a transition from a static + launch chain to the final Operating System. + +:Late Launch: The usage of a dynamic launch by an executing Operating System to + transition to a “known good” state to perform one or more operations, e.g. to + launch into a new Operating System. + +System Integrity +================ + +A computer system can be considered a collection of mechanisms that work +together to produce a result. The assurance that the mechanisms are functioning +correctly and producing the expected result is the integrity of the system. To +ensure a system's integrity there are a subset of these mechanisms, commonly +referred to as security mechanisms, that are present to help ensure the system +produces the expected result or at least detect the potential of an unexpected +result may have happened. Since the security mechanisms are relied upon to +ensue the integrity of the system, these mechanisms are trusted. Upon +inspection these security mechanisms each have a set of properties and these +properties can be evaluated to determine how susceptible a mechanism might be +to failure. This assessment is referred to as the Strength of Mechanism and for +trusted mechanism enables for the trustworthiness of that mechanism to be +quantified. + +For software systems, there are two system states for which the integrity is +critical, when the software is loaded into memory and when the software is +executing on the hardware. Ensuring that the expected software is load into +memory is referred to as load-time integrity while ensuring that the software +executing is the expected software is the runtime integrity of that software. + +Load-time Integrity +------------------- + +It is critical to understand what load-time integrity establishes about a +system and what is assumed, i.e. what is being trusted. Load-time integrity is +when a trusted entity, i.e. an entity with an assumed integrity, takes an +action to assess an entity being loaded into memory before it is used. A +variety of mechanisms may be used to conduct the assessment, each with +different properties. A particular property is whether the mechanism creates an +evidence of the assessment. Often either cryptographic signature checking or +hashing are the common assessment operations used. + +A signature checking assessment functions by requiring a representation of the +accepted authorities and uses those representations to assess if the entity has +been signed by an accepted authority. The benefit to this process is that +assessment process includes an adjudication of the assessment. The drawbacks +are that 1) the adjudication is susceptible to tampering by the Trusted +Computing Base (TCB), 2) there is no evidence to assert that an untampered +adjudication was completed, and 3) the system must be an active participant in +the key management infrastructure. + +A cryptographic hashing assessment does not adjudicate the assessment but +instead, generates evidence of the assessment to be adjudicated independently. +The benefits to this approach is that the assessment may be simple such that it +may be implemented in an immutable mechanism, e.g. in hardware. Additionally, +it is possible for the adjudication to be conducted where it cannot be tampered +with by the TCB. The drawback is that a compromised environment will be allowed +to execute until an adjudication can be completed. + +Ultimately, load-time integrity provides confidence that the correct entity was +loaded and in the absence of a run-time integrity mechanism assumes, i.e. +trusts, that the entity will never become corrupted. + +Runtime Integrity +----------------- + +Runtime integrity in the general sense is when a trusted entity makes an +assessment of an entity at any point in time during the assessed entity's +execution. A more concrete explanation is the taking of an integrity assessment +of an active process executing on the system at any point during the process' +execution. Often the load-time integrity of an operating system's user-space, +i.e. the operating environment, is confused to be the runtime integrity of the +system, since it is an integrity assessment of the "runtime" software. The +reality is that actual runtime integrity is a very difficult problem and thus +not very many solutions are public and/or available. One example of a runtime +integrity solution would be Johns Hopkins Advanced Physics Laboratory's (APL) +Linux Kernel Integrity Module (LKIM). + +Trust Chains +============ + +Building upon the understanding of security mechanisms to establish load-time +integrity of an entity, it is possible to chain together load-time integrity +assessments to establish the integrity of the whole system. This process is +known as transitive trust and provides the concept of building a chain of +load-time integrity assessments, commonly referred to as a trust chain. These +assessments may be used to adjudicate the load-time integrity of the whole +system. This trust chain is started by a trusted entity that does the first +assessment. This first entity is referred to as the Root of Trust(RoT) with the +entities name being derived from the mechanism used for the assessment, i.e. +RoT for Verification (RTV) and RoT for Measurement (RTM). + +A trust chain is itself a mechanism, specifically a mechanism of mechanisms, +and therefore it too has a Strength of Mechanism. The factors that contribute +to the strength of a trust chain are, + + - The strength of the chain's RoT + - The strength of each member of the trust chain + - The length, i.e. the number of members, of the chain + +Therefore, to provide the strongest trust chains, they should start with a +strong RoT and should consist of members being of low complexity and minimizing +the number of members participating as possible. In a more colloquial sense, a +trust chain is only as strong as its weakest link, thus more links increase the +probability of a weak link. + +Dynamic Launch Components +========================= + +The TCG architecture for dynamic launch is composed of a component series that +are used to set up and then carry out the launch. These components work +together to construct an RTM trust chain that is rooted in the dynamic launch +and thus commonly referred to as the Dynamic Root of Trust for Measurement +(DRTM) chain. + +What follows is a brief explanation of each component in execution order. A +subset of these components are what establishes the dynamic launch's trust +chain. + +Dynamic Configuration Environment Preamble +------------------------------------------ + +The Dynamic Configuration Environment (DCE) Preamble is responsible for setting +up the system environment in preparation for a dynamic launch. The DCE Preamble +is not a part of the DRTM trust chain. + +Dynamic Launch Event +-------------------- + +The dynamic launch event is the event, typically a CPU instruction, that +triggers the system's dynamic launch mechanism to begin the launch. The dynamic +launch mechanism is also the RoT for the DRTM trust chain. + +Dynamic Configuration Environment +--------------------------------- + +The dynamic launch mechanism may have resulted in a reset of a portion of the +system. To bring the system back to an adequate state for system software, the +dynamic launch will hand over control to the DCE. Prior to handing over this +control, the dynamic launch, will measure the DCE. Once the DCE is complete it +will proceed to measure and then execute the Dynamic Launch Measured +Environment (DLME). + +Dynamic Launch Measured Environment +----------------------------------- + +The DLME is the first system kernel to have control of the system, but may not +be the last. Depending on the usage and configuration, the DLME may be the +final/target operating system, or it may be a bootloader that will load the +final/target operating system. + +Why DRTM +======== + +It is a fact that DRTM increases the load-time integrity of the system by +providing a trust chain that has an immutable hardware RoT, uses a limited +number of small, special purpose code to establish the trust chain that starts +the target operating system. As mentioned in the Trust Chain section, these are +the main three factors in driving up the strength of a trust chain. As has been +seen with the BootHole exploit, which in fact did not affect the integrity of +DRTM solutions, the sophistication of attacks targeting system launch is at an +all-time high. There is no reason a system should not employ every integrity +measure hardware makes available. This is the crux of a defense-in-depth +approach to system security. In the past, the now closed SMI gap was often +pointed to as invalidating DRTM, which in fact was nothing but a straw man +argument. As has continued to be demonstrated, if/when SMM is corrupted it can +always circumvent all load-time integrity, SRTM and DRTM, because it is a +run-time integrity problem. Regardless, Intel and AMD have both deployed +runtime integrity for SMI and SMM which is tied directly to DRTM such that this +perceived deficiency is now non-existent, and the world is moving forward with +an expectation that DRTM must be present. + +Glossary +======== + +.. glossary:: + integrity + Guarding against improper information modification or destruction, and + includes ensuring information non-repudiation and authenticity. + + - NIST CNSSI No. 4009 - https://www.cnss.gov/CNSS/issuances/Instructions.cfm + + mechanism + A process or system that is used to produce a particular result. + + - NIST Special Publication 800-160 (VOLUME 1 ) - https://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.800-160v1.pdf + + risk + A measure of the extent to which an entity is threatened by a potential + circumstance or event, and typically a function of: (i) the adverse impacts + that would arise if the circumstance or event occurs; and (ii) the + likelihood of occurrence. + + - NIST SP 800-30 Rev. 1 - https://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublication800-30r1.pdf + + security mechanism + A device or function designed to provide one or more security services + usually rated in terms of strength of service and assurance of the design. + + - NIST CNSSI No. 4009 - https://www.cnss.gov/CNSS/issuances/Instructions.cfm + + Strength of Mechanism + A scale for measuring the relative strength of a security mechanism + + - NIST CNSSI No. 4009 - https://www.cnss.gov/CNSS/issuances/Instructions.cfm + + transitive trust + Also known as "Inductive Trust", in this process a Root of Trust gives a + trustworthy description of a second group of functions. Based on this + description, an interested entity can determine the trust it is to place in + this second group of functions. If the interested entity determines that + the trust level of the second group of functions is acceptable, the trust + boundary is extended from the Root of Trust to include the second group of + functions. In this case, the process can be iterated. The second group of + functions can give a trustworthy description of the third group of + functions, etc. Transitive trust is used to provide a trustworthy + description of platform characteristics, and also to prove that + non-migratable keys are in fact non-migratable. + + - TCG Glossary - https://trustedcomputinggroup.org/wp-content/uploads/TCG-Glossary-V1.1-Rev-1.0.pdf + + trust + The confidence one element has in another that the second element will + behave as expected` + + - NISTIR 8320A - https://nvlpubs.nist.gov/nistpubs/ir/2021/NIST.IR.8320A.pdf + + trust anchor + An authoritative entity for which trust is assumed. + + - NIST SP 800-57 Part 1 Rev. 5 - https://nvlpubs.nist.gov/nistpubs/SpecialPublications/NIST.SP.800-57pt1r5.pdf + + trusted + An element that another element relies upon to fulfill critical + requirements on its behalf. + + - NISTIR 8320A - https://nvlpubs.nist.gov/nistpubs/ir/2021/NIST.IR.8320A.pdf + + trusted computing base (TCB) + Totality of protection mechanisms within a computer system, including + hardware, firmware, and software, the combination responsible for enforcing + a security policy. + + - NIST CNSSI No. 4009 - https://www.cnss.gov/CNSS/issuances/Instructions.cfm + + trusted computer system + A system that has the necessary security functions and assurance that the + security policy will be enforced and that can process a range of + information sensitivities (i.e. classified, controlled unclassified + information (CUI), or unclassified public information) simultaneously. + + - NIST CNSSI No. 4009 - https://www.cnss.gov/CNSS/issuances/Instructions.cfm + + trustworthiness + The attribute of a person or enterprise that provides confidence to others + of the qualifications, capabilities, and reliability of that entity to + perform specific tasks and fulfill assigned responsibilities. + + - NIST CNSSI No. 4009 - https://www.cnss.gov/CNSS/issuances/Instructions.cfm diff --git a/Documentation/security/launch-integrity/secure_launch_details.rst b/Documentation/security/launch-integrity/secure_launch_details.rst new file mode 100644 index 000000000000..dfde0ee134ba --- /dev/null +++ b/Documentation/security/launch-integrity/secure_launch_details.rst @@ -0,0 +1,584 @@ +.. SPDX-License-Identifier: GPL-2.0 +.. Copyright © 2019-2023 Daniel P. Smith + +=================================== +Secure Launch Config and Interfaces +=================================== + +:Author: Daniel P. Smith +:Date: October 2023 + +Configuration +============= + +The settings to enable Secure Launch using Kconfig are under:: + + "Processor type and features" --> "Secure Launch support" + +A kernel with this option enabled can still be booted using other supported +methods. + +To reduce the Trusted Computing Base (TCB) of the MLE [1]_, the build +configuration should be pared down as narrowly as one's use case allows. The +fewer drivers (less active hardware) and features reduces the attack surface. +As an example in the extreme, the MLE could only have local disk access with no +other hardware supports, except optional network access for remote attestation. + +It is also desirable, if possible, to embed the initrd used with the MLE kernel +image to reduce complexity. + +The following are a few important configuration necessities to always consider: + +KASLR Configuration +------------------- + +Due to Secure Launch hardware implementation details and how KASLR functions, +Secure Launch is not able to interoperate with KASLR at this time. Attempts to +enable KASLR in a kernel started using Secure Launch may result in crashes and +other instabilities at boot. If possible, a kernel being used as an MLE should +be built with KASLR disabled:: + + "Processor type and features" --> + "Build a relocatable kernel" --> + "Randomize the address of the kernel image (KASLR) [ ]" + +This action unsets the Kconfig value CONFIG_RANDOMIZE_BASE. + +If it is not possible to disable at build time, then it is recommended to force +KASLR to be disabled using the kernel command line when doing a Secure Launch. +The kernel parameter is as follows:: + + nokaslr + +.. note:: + Should KASLR be made capabile of reading/using only the protected page + regions set up by the memory protection mechanisms used by the hardware + DRTM capability, then it would become possible to use KASLR with Secure + Launch. + +IOMMU Configuration +------------------- + +When doing a Secure Launch, the IOMMU should always be enabled and the drivers +loaded. However, IOMMU passthrough mode should never be used. This leaves the +MLE completely exposed to DMA after the PMR's [2]_ are disabled. The current +default mode is to use IOMMU in lazy translated mode, but strict translated +mode is the preferred IOMMU mode and this should be selected in the build +configuration:: + + "Device Drivers" --> + "IOMMU Hardware Support" --> + "IOMMU default domain type" --> + "(X) Translated - Strict" + +In addition, the Intel IOMMU should be on by default. The following sets this as the +default in the build configuration:: + + "Device Drivers" --> + "IOMMU Hardware Support" --> + "Support for Intel IOMMU using DMA Remapping Devices [*]" + +and:: + + "Device Drivers" --> + "IOMMU Hardware Support" --> + "Support for Intel IOMMU using DMA Remapping Devices [*]" --> + "Enable Intel DMA Remapping Devices by default [*]" + +It is recommended that no other command line options should be set to override +the defaults above. If there is a desire to run an alternate configuration, +then that configuration should be evaluated for what benefits are attempting to +be gained against the risks for DMA attacks for which the kernel is likely +going to be exposed. + +Secure Launch Resource Table +============================ + +The Secure Launch Resource Table (SLRT) is a platform-agnostic, standard format +for providing information for the pre-launch environment and to pass +information to the post-launch environment. The table is populated by one or +more bootloaders in the boot chain and used by Secure Launch on how to set up +the environment during post-launch. The details for the SLRT are documented +in the TrenchBoot Secure Launch Specification [3]_. + +Intel TXT Interface +=================== + +The primary interfaces between the various components in TXT are the TXT MMIO +registers and the TXT heap. The MMIO register banks are described in Appendix B +of the TXT MLE [1]_ Development Guide. + +The TXT heap is described in Appendix C of the TXT MLE [1]_ Development +Guide. Most of the TXT heap is predefined in the specification. The heap is +initialized by firmware and the pre-launch environment and is subsequently used +by the SINIT ACM. One section, called the OS to MLE Data Table, is reserved for +software to define. This table is set up per the recommendation detailed in +Appendix B of the TrenchBoot Secure Launch Specification:: + + /* + * Secure Launch defined OS/MLE TXT Heap table + */ + struct txt_os_mle_data { + u32 version; + u32 boot_params_addr; + 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 access to the TPM hardware interface. +This is most likely due to misconfigured hardware or kernel. Ensure the TPM +chip is enabled, and the kernel TPM support is built in (it should not be built +as a module). + +====== ========================== +Name: SL_ERROR_TPM_INVALID_LOG20 +Value: 0xc0008003 +====== ========================== + +Description: + +The Secure Launch code failed to find a valid event log descriptor for a +version 2.0 TPM or the event log descriptor is malformed. Usually this +indicates there are incompatible versions of the pre-launch environment and the +MLE kernel. The pre-launch environment and the kernel share a structure in the +TXT heap and if this structure (the OS-MLE table) is mismatched, this error is +often seen. This TXT heap area is set up by the pre-launch environment, so the +issue may originate there. It could also be the sign of an attempted attack. + +====== =========================== +Name: SL_ERROR_TPM_LOGGING_FAILED +Value: 0xc0008004 +====== =========================== + +Description: + +There was a failed attempt to write a TPM event to the event log early in the +Secure Launch process. This is likely the result of a malformed TPM event log +buffer. Formatting of the event log buffer information is done by the +pre-launch environment, so the issue most likely originates there. + +====== ============================ +Name: SL_ERROR_REGION_STRADDLE_4GB +Value: 0xc0008005 +====== ============================ + +Description: + +During early validation, a buffer or region was found to straddle the 4GB +boundary. Because of the way TXT does DMA memory protection, this is an unsafe +configuration and is flagged as an error. This is most likely a configuration +issue in the pre-launch environment. It could also be the sign of an attempted +attack. + +====== =================== +Name: SL_ERROR_TPM_EXTEND +Value: 0xc0008006 +====== =================== + +Description: + +There was a failed attempt to extend a TPM PCR in the Secure Launch platform +module. This is most likely to due to misconfigured hardware or kernel. Ensure +the TPM chip is enabled, and the kernel TPM support is built in (it should not +be built as a module). + +====== ====================== +Name: SL_ERROR_MTRR_INV_VCNT +Value: 0xc0008007 +====== ====================== + +Description: + +During early Secure Launch validation, an invalid variable MTRR count was +found. The pre-launch environment passes a number of MSR values to the MLE to +restore including the MTRRs. The values are restored by the Secure Launch early +entry point code. After measuring the values supplied by the pre-launch +environment, a discrepancy was found, validating the values. It could be the +sign of an attempted attack. + +====== ========================== +Name: SL_ERROR_MTRR_INV_DEF_TYPE +Value: 0xc0008008 +====== ========================== + +Description: + +During early Secure Launch validation, an invalid default MTRR type was found. +See SL_ERROR_MTRR_INV_VCNT for more details. + +====== ====================== +Name: SL_ERROR_MTRR_INV_BASE +Value: 0xc0008009 +====== ====================== + +Description: + +During early Secure Launch validation, an invalid variable MTRR base value was +found. See SL_ERROR_MTRR_INV_VCNT for more details. + +====== ====================== +Name: SL_ERROR_MTRR_INV_MASK +Value: 0xc000800a +====== ====================== + +Description: + +During early Secure Launch validation, an invalid variable MTRR mask value was +found. See SL_ERROR_MTRR_INV_VCNT for more details. + +====== ======================== +Name: SL_ERROR_MSR_INV_MISC_EN +Value: 0xc000800b +====== ======================== + +Description: + +During early Secure Launch validation, an invalid miscellaneous enable MSR +value was found. See SL_ERROR_MTRR_INV_VCNT for more details. + +====== ========================= +Name: SL_ERROR_INV_AP_INTERRUPT +Value: 0xc000800c +====== ========================= + +Description: + +The application processors (APs) wait to be woken up by the SMP initialization +code. The only interrupt that they expect is an NMI; all other interrupts +should be masked. If an AP gets some other interrupt other than an NMI, it will +cause this error. This error is very unlikely to occur. + +====== ========================= +Name: SL_ERROR_INTEGER_OVERFLOW +Value: 0xc000800d +====== ========================= + +Description: + +A buffer base and size passed to the MLE caused an integer overflow when +added together. This is most likely a configuration issue in the pre-launch +environment. It could also be the sign of an attempted attack. + +====== ================== +Name: SL_ERROR_HEAP_WALK +Value: 0xc000800e +====== ================== + +Description: + +An error occurred in TXT heap walking code. The underlying issue is a failure to +early_memremap() portions of the heap, most likely due to a resource shortage. + +====== ================= +Name: SL_ERROR_HEAP_MAP +Value: 0xc000800f +====== ================= + +Description: + +This error is essentially the same as SL_ERROR_HEAP_WALK but occurred during the +actual early_memremap() operation. + +====== ========================= +Name: SL_ERROR_REGION_ABOVE_4GB +Value: 0xc0008010 +====== ========================= + +Description: + +A memory region used by the MLE is above 4GB. In general this is not a problem +because memory > 4Gb can be protected from DMA. There are certain buffers that +should never be above 4Gb, and one of these caused the violation. This is most +likely a configuration issue in the pre-launch environment. It could also be +the sign of an attempted attack. + +====== ========================== +Name: SL_ERROR_HEAP_INVALID_DMAR +Value: 0xc0008011 +====== ========================== + +Description: + +The backup copy of the ACPI DMAR table which is supposed to be located in the +TXT heap could not be found. This is due to a bug in the platform's ACM module +or in firmware. + +====== ======================= +Name: SL_ERROR_HEAP_DMAR_SIZE +Value: 0xc0008012 +====== ======================= + +Description: + +The backup copy of the ACPI DMAR table in the TXT heap is to large to be stored +for later usage. This error is very unlikely to occur since the area reserved +for the copy is far larger than the DMAR should be. + +====== ====================== +Name: SL_ERROR_HEAP_DMAR_MAP +Value: 0xc0008013 +====== ====================== + +Description: + +The backup copy of the ACPI DMAR table in the TXT heap could not be mapped. The +underlying issue is a failure to early_memremap() the DMAR table, most likely +due to a resource shortage. + +====== ==================== +Name: SL_ERROR_HI_PMR_BASE +Value: 0xc0008014 +====== ==================== + +Description: + +On a system with more than 4G of RAM, the high PMR [2]_ base address should be +set to 4G. This error is due to that not being the case. This PMR value is set +by the pre-launch environment, so the issue most likely originates there. It +could also be the sign of an attempted attack. + +====== ==================== +Name: SL_ERROR_HI_PMR_SIZE +Value: 0xc0008015 +====== ==================== + +Description: + +On a system with more than 4G of RAM, the high PMR [2]_ size should be set to +cover all RAM > 4G. This error is due to that not being the case. This PMR +value is set by the pre-launch environment, so the issue most likely originates +there. It could also be the sign of an attempted attack. + +====== ==================== +Name: SL_ERROR_LO_PMR_BASE +Value: 0xc0008016 +====== ==================== + +Description: + +The low PMR [2]_ base should always be set to address zero. This error is due +to that not being the case. This PMR value is set by the pre-launch environment +so the issue most likely originates there. It could also be the sign of an +attempted attack. + +====== ==================== +Name: SL_ERROR_LO_PMR_MLE +Value: 0xc0008017 +====== ==================== + +Description: + +This error indicates the MLE image is not covered by the low PMR [2]_ range. +The PMR values are set by the pre-launch environment, so the issue most likely +originates there. It could also be the sign of an attempted attack. + +====== ======================= +Name: SL_ERROR_INITRD_TOO_BIG +Value: 0xc0008018 +====== ======================= + +Description: + +The external initrd provided is larger than 4Gb. This is not a valid +configuration for a Secure Launch due to managing DMA protection. + +====== ========================= +Name: SL_ERROR_HEAP_ZERO_OFFSET +Value: 0xc0008019 +====== ========================= + +Description: + +During a TXT heap walk, an invalid/zero next table offset value was found. This +indicates the TXT heap is malformed. The TXT heap is initialized by the +pre-launch environment, so the issue most likely originates there. It could +also be a sign of an attempted attack. In addition, ACM is also responsible for +manipulating parts of the TXT heap, so the issue could be due to a bug in the +platform's ACM module. + +====== ============================= +Name: SL_ERROR_WAKE_BLOCK_TOO_SMALL +Value: 0xc000801a +====== ============================= + +Description: + +The AP wake block buffer passed to the MLE via the OS-MLE TXT heap table is not +large enough. This value is set by the pre-launch environment, so the issue +most likely originates there. It also could be the sign of an attempted attack. + +====== =========================== +Name: SL_ERROR_MLE_BUFFER_OVERLAP +Value: 0xc000801b +====== =========================== + +Description: + +One of the buffers passed to the MLE via the OS-MLE TXT heap table overlaps +with the MLE image in memory. This value is set by the pre-launch environment +so the issue most likely originates there. It could also be the sign of an +attempted attack. + +====== ========================== +Name: SL_ERROR_BUFFER_BEYOND_PMR +Value: 0xc000801c +====== ========================== + +Description: + +One of the buffers passed to the MLE via the OS-MLE TXT heap table is not +protected by a PMR. This value is set by the pre-launch environment, so the +issue most likely originates there. It could also be the sign of an attempted +attack. + +====== ============================= +Name: SL_ERROR_OS_SINIT_BAD_VERSION +Value: 0xc000801d +====== ============================= + +Description: + +The version of the OS-SINIT TXT heap table is bad. It must be 6 or greater. +This value is set by the pre-launch environment, so the issue most likely +originates there. It could also be the sign of an attempted attack. It is also +possible though very unlikely that the platform is so old that the ACM being +used requires an unsupported version. + +====== ===================== +Name: SL_ERROR_EVENTLOG_MAP +Value: 0xc000801e +====== ===================== + +Description: + +An error occurred in the Secure Launch module while mapping the TPM event log. +The underlying issue is memremap() failure, most likely due to a resource +shortage. + +====== ======================== +Name: SL_ERROR_TPM_NUMBER_ALGS +Value: 0xc000801f +====== ======================== + +Description: + +The TPM 2.0 event log reports an unsupported number of hashing algorithms. +Secure launch currently only supports a maximum of two: SHA1 and SHA256. + +====== =========================== +Name: SL_ERROR_TPM_UNKNOWN_DIGEST +Value: 0xc0008020 +====== =========================== + +Description: + +The TPM 2.0 event log reports an unsupported hashing algorithm. Secure launch +currently only supports two algorithms: SHA1 and SHA256. + +====== ========================== +Name: SL_ERROR_TPM_INVALID_EVENT +Value: 0xc0008021 +====== ========================== + +Description: + +An invalid/malformed event was found in the TPM event log while reading it. +Since only trusted entities are supposed to be writing the event log, this +would indicate either a bug or a possible attack. + +====== ===================== +Name: SL_ERROR_INVALID_SLRT +Value: 0xc0008022 +====== ===================== + +Description: + +The Secure Launch Resource Table is invalid or malformed and is unusable. This +implies the pre-launch code did not properly set up the SLRT. + +====== =========================== +Name: SL_ERROR_SLRT_MISSING_ENTRY +Value: 0xc0008023 +====== =========================== + +Description: + +The Secure Launch Resource Table is missing a required entry within it. This +implies the pre-launch code did not properly set up the SLRT. + +====== ================= +Name: SL_ERROR_SLRT_MAP +Value: 0xc0008024 +====== ================= + +Description: + +An error occurred in the Secure Launch module while mapping the Secure Launch +Resource table. The underlying issue is memremap() failure, most likely due to +a resource shortage. + +.. [1] + MLE: Measured Launch Environment is the binary runtime that is measured and + then run by the TXT SINIT ACM. The TXT MLE Development Guide describes the + requirements for the MLE in detail. + +.. [2] + PMR: Intel VTd has a feature in the IOMMU called Protected Memory Registers. + There are two of these registers and they allow all DMA to be blocked + to large areas of memory. The low PMR can cover all memory below 4Gb on 2Mb + boundaries. The high PMR can cover all RAM on the system, again on 2Mb + boundaries. This feature is used during a Secure Launch by TXT. + +.. [3] + Secure Launch Specification: https://trenchboot.org/specifications/Secure_Launch/ diff --git a/Documentation/security/launch-integrity/secure_launch_overview.rst b/Documentation/security/launch-integrity/secure_launch_overview.rst new file mode 100644 index 000000000000..b01d29fff012 --- /dev/null +++ b/Documentation/security/launch-integrity/secure_launch_overview.rst @@ -0,0 +1,226 @@ +.. SPDX-License-Identifier: GPL-2.0 +.. Copyright © 2019-2023 Daniel P. Smith + +====================== +Secure Launch Overview +====================== + +:Author: Daniel P. Smith +:Date: October 2023 + +Overview +======== + +Prior to the start of the TrenchBoot project, the only active Open Source +project supporting dynamic launch was Intel's tboot project to support their +implementation of dynamic launch known as Intel Trusted eXecution Technology +(TXT). The approach taken by tboot was to provide an exokernel that could +handle the launch protocol implemented by Intel's special loader, the SINIT +Authenticated Code Module (ACM [2]_) and remained in memory to manage the SMX +CPU mode that a dynamic launch would put a system. While it is not precluded +from being used for doing a late launch, tboot's primary use case was to be +used as an early launch solution. As a result, the TrenchBoot project started +the development of Secure Launch kernel feature to provide a more generalized +approach. The focus of the effort is twofold, the first is to make the Linux +kernel directly aware of the launch protocol used by Intel, AMD/Hygon, Arm, and +potentially OpenPOWER. The second is to make the Linux kernel be able to +initiate a dynamic launch. It is through this approach that the Secure Launch +kernel feature creates a basis for the Linux kernel to be used in a variety of +dynamic launch use cases. + +.. note:: + A quick note on terminology. The larger open source project itself is + called TrenchBoot, which is hosted on GitHub (links below). The kernel + feature enabling the use of the x86 technology is referred to as "Secure + Launch" within the kernel code. + +Goals +===== + +The first use case that the TrenchBoot project focused on was the ability for +the Linux kernel to be started by a dynamic launch, in particular as part of an +early launch sequence. In this case, the dynamic launch will be initiated by +any bootloader with associated support added to it, for example the first +targeted bootloader in this case was GRUB2. An integral part of establishing a +measurement-based launch integrity involves measuring everything that is +intended to be executed (kernel image, initrd, etc.) and everything that will +configure that kernel to execute (command line, boot params, etc.). Then +storing those measurements in a protected manner. Both the Intel and AMD +dynamic launch implementations leverage the Trusted Platform Module (TPM) to +store those measurements. The TPM itself has been designed such that a dynamic +launch unlocks a specific set of Platform Configuration Registers (PCR) for +holding measurement taken during the dynamic launch. These are referred to as +the DRTM PCRs, PCRs 17-22. Further details on this process can be found in the +documentation for the GETSEC instruction provided by Intel's TXT and the SKINIT +instruction provided by AMD's AMD-V. The documentation on these technologies +can be readily found online; see the `Resources`_ section below for references. + +.. note:: + Currently, only Intel TXT is supported in this first release of the Secure + Launch feature. AMD/Hygon SKINIT and Arm support will be added in a + subsequent release. + +To enable the kernel to be launched by GETSEC a stub, the Secure Launch stub, +must be built into the setup section of the compressed kernel to handle the +specific state that the dynamic launch process leaves the BSP. Also, the Secure +Launch stub must measure everything that is going to be used as early as +possible. This stub code and subsequent code must also deal with the specific +state that the dynamic launch leaves the APs as well. + +Design Decisions +================ + +A number of design decisions were made during the development of the Secure +Launch feature. The two primary guiding decisions were: + + - Keeping the Secure Launch code as separate from the rest of the kernel + as possible. + - Modifying the existing boot path of the kernel as little as possible. + +The following illustrate how the implementation followed these design +decisions: + + - All the entry point code necessary to properly configure the system post + launch is found in st_stub.S in the compressed kernel image. This code + validates the state of the system, restores necessary system operating + configurations and properly handles post launch CPU states. + - After the sl_stub.S is complete, it jumps directly to the unmodified + startup_32 kernel entry point. + - A single call is made to a function sl_main() prior to the main kernel + decompression step. This code performs further validation and takes the + needed DRTM measurements. + - After the call to sl_main(), the main kernel is decompressed and boots as + it normally would. + - Final setup for the Secure Launch kernel is done in a separate Secure + Launch module that is loaded via a late initcall. This code is responsible + for extending the measurements taken earlier into the TPM DRTM PCRs and + setting up the securityfs interface to allow access to the TPM event log and + public TXT registers. + - On the reboot and kexec paths, calls are made to a function to finalize the + state of the Secure Launch kernel. + +The one place where Secure Launch code is mixed directly in with kernel code is +in the SMP boot code. This is due to the unique state that the dynamic launch +leaves the APs in. On Intel, this involves using a method other than the +standard INIT-SIPI sequence. + +A final note is that originally the extending of the PCRs was completed in the +Secure Launch stub when the measurements were taken. An alternative solution +had to be implemented due to the TPM maintainers objecting to the PCR +extensions being done with a minimal interface to the TPM that was an +independent implementation of the mainline kernel driver. Since the mainline +driver relies heavily on kernel interfaces not available in the compressed +kernel, it was not possible to reuse the mainline TPM driver. This resulted in +the decision to move the extension operations to the Secure Launch module in +the mainline kernel, where the TPM driver would be available. + +Basic Boot Flow +=============== + +Outlined here is a summary of the boot flow for Secure Launch. A more detailed +review of Secure Launch process can be found in the Secure Launch +Specification, a link is located in the `Resources`_ section. + +Pre-launch: *Phase where the environment is prepared and configured to initiate +the secure launch by the boot chain.* + + - The SLRT is initialized and dl_stub is placed in memory. + - Load the kernel, initrd and ACM [2]_ into memory. + - Set up the TXT heap and page tables describing the MLE [1]_ per the + specification. + - If non-UEFI platform, dl_stub is called. + - If UEFI platforms, SLRT registered with UEFI and efi-stub called. + - Upon completion, efi-stub will call EBS followed by dl_stub. + - The dl_stub will prepare the CPU and the TPM for the launch. + - The secure launch is then initiated with the GETSET[SENTER] instruction. + +Post-launch: *Phase where control is passed from the ACM to the MLE and the secure +kernel begins execution.* + + - Entry from the dynamic launch jumps to the SL stub. + - SL stub fixes up the world on the BSP. + - For TXT, SL stub wakes the APs, fixes up their worlds. + - For TXT, APs are left halted 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.