]> Google LLC

dionnaglaze@google.com

Security Remote ATtestation ProcedureS RIM, RATS, attestation, verifier, supply chain AMD Secure Encrypted Virtualization with Secure Nested Pages (SEV-SNP) attestation reports comprise of reference values and cryptographic key material that a Verifier needs in order to appraise Attestation Evidence produced by an AMD SEV-SNP virtual machine. This document specifies the information elements for representing SEV-SNP Reference Values in CoRIM format. Discussion Venues Source for this draft and an issue tracker can be found at .

Introduction This profile describes the extensions and restrictions placed on Reference Values, Endorsements, and Evidence that support the attestation capabilities of AMD products that provide Securet Encrypted Virtualization with Secure Nested Pages (SEV-SNP). CoRIM () defines a baseline CDDL for Reference Values and Endorsements that this profile extends. Some measurement types of the baseline CDDL are not used in this profile. The AMD SEV-SNP attestation report byte format is specified by AMD. The profile defines a transformation from the AMD byte format into a CoMID representation for use in appraisal. This profile is meant for expressing reference values and endorsements of specific environments. It is not meant to encode complex policy decisions about the acceptability of measurements. The accepted claim set construction (ACS) this profile enables does lay a foundation for policy engines that enable further evaluation over complete ACS constructions. This profile extends the flags-map to represent the guest policy and host platform info that are unique to AMD SEV-SNP. The profile extends the $crypto-key-type-choice to represent the SHA-384 digest of a key in AMD format from Appendix: Digital Signatures of .

Conventions and Definitions The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 RFC2119 when, and only when, they appear in all capitals, as shown here. The reader is assumed to be familiar with the terms defined in and Section 4 of . The syntax of data descriptions is CDDL as specified in . Fields of the AMD SEV-SNP ATTESTATION_REPORT are referred to by their assigned names in .

AMD SEV-SNP Attestation Reports The AMD SEV-SNP attestation scheme in contains measurements of security-relevant configuration of the host environment and the launch configuration of a SEV-SNP VM. This draft documents the normative representation of attestation report Evidence as a CoRIM profile. AMD-SP: AMD Secure Processor. A separate core that provides the confidentiality and integrity properties of AMD SEV-SNP. The function that is relevant to this document is its construction of signed virtual machine attestation reports. : Versioned Chip Endorsement Key. A key for signing the SEV-SNP Attestation Report. The key is derived from a unique device secret as well as the security patch levels of relevant host components. : Version Loaded Endorsement Key. An alternative SEV-SNP Attestation Report signing key that is derived from a secret shared between AMD and a Cloud Service Provider. The key is encrypted with a per-device per-version wrapping key that is then decrypted and stored by the AMD-SP. VEK: Either a VCEK or VLEK.

AMD SEV-SNP CoRIM Profile AMD SEV-SNP launch endorsements are carried in one or more CoMIDs inside a CoRIM. The profile attribute in the CoRIM MAY be present to specify a further restriction on this profile. The base requirements of this profile MAY be specified by tag:amd.com,2024:snp-corim-profile .

SEV-SNP attestation profile version 1, CoRIM profile

AMD SEV-SNP Target Environment The ATTESTATION_REPORT structure as understood in the RATS Architecture is a signed collection of Claims that constitute Evidence about the Target Environment. The Attester for the ATTESTATION_REPORT is specialized hardware that will only run AMD-signed firmware. The instance identifier can be argued as any of REPORT_ID, REPORT_ID_MA when non-zero, CHIP_ID (for VCEK), or CSP_ID (for VLEK). Given that REPORT_ID and REPORT_ID_MA are more ephemeral measured values and not the instance of the AMD-SP as the attesting environment, they are relegated to measurements. Any endorsement of VM instances specific to either the REPORT_ID or REPORT_ID_MA values SHOULD use a conditional endorsement triple. The different notions of identity induce different classes of attestation to identify target environments. The different classes of attestation are

• By chip: The environment-map / instance is 560(CHIP_ID).
• By CSP: The environment-map / instance is 560(CSP_ID).

The CSP_ID is only evident from the VLEK certificate, which uses the ASN.1 IA5String encoding. For the tagged-bytes representation, however, the CSP_ID SHALL be the UTF-8 encoding of the text string. The class-id for the Target Environment measured by the AMD-SP is a tagged OID that corresponds to the attestation class:

• By chip: 1.3.6.1.4.1.3704.3.1 (111(h'06092b060104019c780301'))
• By CSP: 1.3.6.1.4.1.3704.3.2 (111(h'06092b060104019c780302'))

The model field MUST NOT be present in the environment-map, as it is error-prone to determine for VERSION 2, and redundant with fields added in VERSION 3. The rest of the class-map MUST remain empty, since class is compared for deterministic CBOR binary encoding equality. The group is free for a CoRIM issuer to assign. If the SIGNING_KEY bit of the attestation report is 1 indicating VLEK use, then the class-id MUST NOT be by chip. #6.111(h'06092b060104019c780301') } / instance: / 1 => #6.560(CHIP_ID) } ]]>

AMD SEV-SNP Attestation Report measurements The fields of an attestation report are named by mkey numbers that map to appropriate measurement-values-map values. This profile defines no new measurement-values-map extensions for the $$measurement-values-map-extensions socket. Flag-like values are delegated to the raw-value and raw-value-mask measurement values.

AMD SEV-SNP measurements The measurements in an ATTESTATION_REPORT are each assigned an mkey value and the field value is translated to an appropriate measurement-values-map entry. The convention for mkey value assignment is to sequential ordering when there are no reserved bits. The mkey following a reserved bit is the bit position in the report of the start of the value. The R[lo:hi] notation will reference the attestation report byte slice from offset lo inclusive to hi exclusive. The leuintN type is another name for a byte string, but with the interpretation that it represents an unsigned integer with N bit width. mkey 0: VERSION. Expressed as &(raw-value: 4): tagged-leuint32. mkey 1: GUEST_SVN. Expressed as &(raw-value: 4): tagged-bytes4. mkey 2: POLICY. Expressed as &(raw-value: 4): tagged-bytes8 with optional &(raw-value-mask: 5): tagged-bytes8 to restrict the reference value to the masked bits. mkey 3: FAMILY_ID. Expressed as &(raw-value: 4): tagged-bytes16. mkey 4: IMAGE_ID. Expressed as &(raw-value: 4): tagged-bytes16. mkey 5: VMPL. Expressed as &(raw-value: 4): tagged-leuint32. SIGNATURE_ALGO skipped: R[0x034:0x38] only needed for signature verification. mkey 6: CURRENT_TCB. Expressed as &(svn: 1): svn-type .and svn64-type mkey 7: PLATFORM_INFO. Expressed as &(raw-value: 4): tagged-bytes8 with optional &(raw-value-mask: 5): tagged-bytes8 to restrict the reference value to the masked bits. AUTHOR_KEY_EN skipped: AUTHOR_KEY_DIGEST will be present in evidence if and only if this bit is 1. MASK_CHIP_KEY skipped: CHIP_ID will be present in evidence if and only if this bit is 0. SIGNING_KEY skipped: The environment's class is determined by the attestation key kind. mkey 640: REPORT_DATA. Expressed as &(raw-value: 4): tagged-bytes64. mkey 641: MEASUREMENT. Expressed as &(digests: 2): [[7, bytes48]]. mkey 642: HOST_DATA. Expressed as &(digests: 2): [[7, bytes48]]. mkey 643: ID_KEY_DIGEST. Expressed as &(digests: 2): [[7, bytes48]]. mkey 644: AUTHOR_KEY_DIGEST. Expressed as &(digests: 2): [[7, bytes48]]. mkey 645: REPORT_ID. Expressed as &(raw-value: 4): tagged-bytes32 mkey 646: REPORT_ID_MA. Expressed as &(raw-value: 4): tagged-bytes32 mkey 647: REPORTED_TCB Expressed as &(svn: 1): svn64-type. mkey 648: CPUID_FAM_ID. Expressed as &(raw-value: 4): tagged-byte. mkey 649: CPUID_MOD_ID. Expressed as &(raw-value: 4): tagged-byte. mkey 650: CPUID_STEP. Expressed as &(raw-value: 4): tagged-byte. mkey 3328: CHIP_ID. Expressed as &(raw-value: 4): tagged-bytes64. mkey 3329: COMMITTED_TCB: Expressed as &(svn: 1): svn64-type. mkey 3330: CurrentVersion. Expressed as &(version: 0): semver-version-map mkey 3936: CommittedVersion. Expressed as &(version: 0): semver-version-map mkey 3968: LAUNCH_TCB. Expressed as &(svn: 1): svn64-type.

AMD SEV-SNP Evidence Translation to reference-triple-record The ATTESTATION_REPORT Evidence is converted into a CoRIM internal representation given the canonical translation from a reference-triple-record as evidence conceptual message.

environment If SIGNING_KEY is 0

• The environment-map / class / class-id field SHALL be set to 111(h'06092b060104019c780301').
• The environment-map / instance field
  • MAY be 560(CHIP_ID) only if MASK_CHIP_KEY is 0, or
  • MAY be 560(hwid) where hwid is from the VCEK certificate extension value of 1.3.6.1.4.1.3704.1.4.

If SIGNING_KEY is 1

• The environment-map / class / class-id field SHALL be set to 111(h'06092b060104019c780302').
• The environment-map / instance field SHALL be 560(CSP_ID).

The Verifier is free add a group according to vendor-defined rules.

measurement-map The translation makes use of the following metafunctions:

• The function dec(b) represents a byte in its decimal string rendering.

Juxtaposition of expressions with string literals is interpreted with string concatenation. Note: A value of 0 is not treated the same as unset given the semantics for matching flags-map. no mkey: The &(flags: 3) codepoint SHALL be set to a flags-map with the following construction:

• is-confidentiality-protected MAY be set to true.
• is-integrity-protected MAY be set to true.
• is-replay-protected MAY be set to true.
• is-debug SHALL be set to the truth value of bit 19 of POLICY.

mkey 0: VERSION. The codepoint &(raw-value: 4) SHALL be set to 560(R[0x000:0x004]). mkey 1: GUEST_SVN. 4 bytes. The codepoint &(raw-value: 4) SHALL be set to 560(R[0x004:0x008]). mkey 2: POLICY. 8 bytes. The codepoint &(raw-value: 4) SHALL be set to 560:(R[0x008:0x010]) with optional &(raw-value-mask: 5): tagged-bytes to restrict the reference value to the masked bits. mkey 3: FAMILY_ID. 16 bytes. The codepoint &(raw-value: 4) SHALL be set to 560:(R[0x010:0x020]). mkey 4: IMAGE_ID. 16 bytes. The codepoint &(raw-value: 4) SHALL be set to 560:(R[0x020:0x030]). mkey 5: VMPL. 4 bytes. The codepoint &(raw-value: 4) SHALL be set to 560:(R[0x030:0x034]). SIGNATURE_ALGO skipped: R[0x034:0x38] only needed for signature verification. mkey 6: CURRENT_TCB. The codepoint &(svn: 1) SHALL be set to 552(current_tcb) where current_tcb is R[0x038:0x40] translated to uint from its little-endian representation. mkey 7: PLATFORM_INFO. The codepoint &(raw-value: 4) SHALL be set to 560(R[0x040:0x048]). AUTHOR_KEY_EN skipped: AUTHOR_KEY_DIGEST will be present in evidence if and only if this bit is 1. MASK_CHIP_KEY skipped: CHIP_ID will be present in evidence if and only if this bit is 0. SIGNING_KEY skipped: The environment's class is determined by the attestation key kind. mkey 640: REPORT_DATA. The codepoint &(raw-value: 4) SHALL be set to 560(R[0x050:0x090]). mkey 641: MEASUREMENT. The codepoint &(digests: 2) SHALL be set to [[7, R[0x090:0x0C0]]]. **mkey 642: HOST_DATA. The codepoint &(digests: 2) SHALL be set to [[7, R[0x0C0:0x0E0]]]. mkey 643: ID_KEY_DIGEST. The codepoint &(digests: 2): [[7, R[0x0E0:0x110]]] SHALL be set. mkey 644: AUTHOR_KEY_DIGEST. The codepoint &(digests: 2) SHALL be set to [[7, R[0x110:0x140]]] only if AUTHOR_KEY_EN (R[0x048] & 1) is 1. mkey 645: REPORT_ID. The codepoint &(raw-value: 4) SHALL be set to 560(R[0x140:0x160]) mkey 646: REPORT_ID_MA. The codepoint &(raw-value: 4) SHALL be set to 560(R[0x160:0x180]) only if non-zero. mkey 647: REPORTED_TCB The codepoint &(svn: 1) SHALL be set to 552(reported_tcb) where reported_tcb is REPORTED_TCB (R[0x180:0x188]) translated to uint from its little-endian representation. mkey 648: CPUID_FAM_ID. The codepoint &(raw-value: 4) SHALL be set to 560(R[0x188:0x189]) only if VERSION (little endian R[0x000:0x004]) is at least 3. mkey 649: CPUID_MOD_ID. The codepoint &(raw-value: 4) SHALL be set to 560(R[0x189:0x18A]) only if VERSION (little endian R[0x000:0x004]) is at least 3. mkey 650: CPUID_STEP. The codepoint &(raw-value: 4) SHALL be set to 560(R[0x18A:0x18B]) only if VERSION (little endian R[0x000:0x004]) is at least 3. mkey 3328: CHIP_ID. The codepoint &(raw-value: 4) SHALL be set to 560(R[0x1A0:0x1E0]) only if MASK_CHIP_KEY (R[0x048] & 2) is 0. mkey 3329: COMMITTED_TCB. The codepoint &(svn: 1) SHALL be set to 552(committed_tcb) where committed_tcb is REPORTED_TCB (R[0x1E0:0x1E8]) translated to uint from its little-endian representation. mkey 3330: CurrentVersion. The &(version: 0) codepoint SHALL be set to The version string vstr is constructed as dec(R[0x1EA]) '.' dec(R[0x1E9]) '.' dec(R[0x1E8]). mkey 3936: CommittedVersion. The &(version: 0) codepoint SHALL be set to The version string vstr is constructed as dec(R[0x1EE]) '.' dec(R[0x1ED]) '.' dec(R[0x1EC]). mkey 3968: LAUNCH_TCB. The codepoint &(svn: 1) SHALL be set to 552(launch_tcb) where launch_tcb is LAUNCH_TCB (R[0x1F0:0x1F8]) translated to uint from its little-endian representation.

cmtype The cmtype SHALL be evidence: 2.

Optional: ID block as reference value If an ID block is provided at VM launch, it is authenticated by an ID key. The ID block authentication is checked by the AMD-SP firmware. The firmware will only launch the VM if the authenticated policy matches. The firmware indicates that the authentication passed by populating fields of the attestation report to bind the evidence to the authentication key(s) ID_KEY_DIGEST and/or AUTHOR_KEY_DIGEST. The ID block authentication as reference value SHALL NOT be retained by the Verifier to apply to another appraisal session. The reference value qualification is meant to be considered valid only for the duration of the appraisal session. The Verifier MAY allocate an rv for an addition ECT to represent the authentication at SNP_LAUNCH_FINISH.

• The environment SHALL be equal to the environment of the evidence ECT.
• The element-list SHALL contain two element-map entries
  • The first element-map SHALL set element-id to 0 and the element-claims to a copy of the evidence claims for element-id: 0.
  • The second element-map SHALL set element-id to 1 and the element-claims to a copy of the evidence claims for element-id: 1.
• The authority SHALL be an array containing #6.TBD(ID_KEY_DIGEST) and #6.TBD(AUTHOR_KEY_DIGEST) if nonzero. The Verifier MAY add more encodings of the same keys.
• The cmtype SHALL be set to reference-values: 0

VEK Certificate attest-key-triple-record Each VEK Certificate from AMD's Key Distribution Service (KDS) contains extensions that associate the key to its target environment. There is no condition on REPORTED_TCB to form this association, since the keys will only ever verify evidence that corresponds the the REPORTED_TCB they were derived from. To allow for certificates to be reissued, the keys associated to an environment use only the SubjectPublicKeyInfo. For consistent comparison, the $crypto-key-type-choice encoding is a #6.557-tagged SHA256 digest (alg: 1) of the ASN.1 encoding as defined in [RFC5280]. Let vcek_pk represent the tagged key identifier of the VCEK public key. A certificate may be interpreted with hwid as the octet-string value from X.509 extension 1.3.6.1.4.1.3704.1.4 as Note: KDS may not encode the hwid with the octet string type tag 0x04 and length information (definite, short, 64) 0x40 of the x.509 extension value. If the length is 64 bytes, then that is the exact hwid. Let vlek_pk be the encoded VLEK public key. A certificate SHALL be associated with an environment with a "by CSP" class-id and instance value as a tagged-bytes of the UTF-8 encoded csp_id string from X.509 extension 1.3.6.1.4.1.3704.1.5 as It is expected that the Verifier will require or admit a trust anchor that associates the AMD root key and AMD SEV key certificates for a product_name (from KDS endpoint vcek/v1/{product_name}/cert_chain or vlek/v1/{product_name}/cert_chain) with the appropriate environment class in order to validate the attestation key certificates. If using a CoTS tag for trust anchor specification, an appropriate purpose for verifying a VEK cerificate is "eat".

IANA Considerations

New CBOR Tags IANA is requested to allocate the following tags in the "CBOR Tags" registry . Added CBOR tags

Tag	Data Item	Semantics	Reference
32780	bytes	A digest of an AMD public key format.	RFCthis

New media types

application/vnd.amd.sev-snp.attestation-report A byte string that is expected to be interpreted as an AMD SEV-SNP ATTESTATION_REPORT.

application/vnd.amd.ghcb.guid-table An byte string that follows the 's GUID table ABI, which is the same as the service manifest ABI, recounted here. A GUID table is a header followed by an byte string body. The header is a sequence of entries described in terminated by an all zero entry. After the all zero entry are the bytes that the header entries index into. guid_table_entry type description

Type	Name	Description
UUID	GUID	An byte format UUID
LE_UINT32	Offset	An offset into the the GUID table
LE_UINT32	Length	A byte length of the span

An LE_UINT32 is a 4 byte byte string that represents a nonnegative integer in little-endian order. Note that an offset is from the start of the byte string, and not from the start of the octets following the zero entry of the header. A header entry is valid if its Offset+Length is less than or equal to the size of the entire GUID table.

New CoAP Content-Formats entries The content types application/vnd.amd.sev-snp.attestation-report and application/vnd.amd.ghcb.guid-table need Content-Formats IDs to be used in the EAT measurements` claim. Requesting 10572 and 10573 respectively.

References Normative References This specification defines a Uniform Resource Name namespace for UUIDs (Universally Unique IDentifier), also known as GUIDs (Globally Unique IDentifier). A UUID is 128 bits long, and can guarantee uniqueness across space and time. UUIDs were originally used in the Apollo Network Computing System and later in the Open Software Foundation\'s (OSF) Distributed Computing Environment (DCE), and then in Microsoft Windows platforms. This specification is derived from the DCE specification with the kind permission of the OSF (now known as The Open Group). Information from earlier versions of the DCE specification have been incorporated into this document. [STANDARDS-TRACK] RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. This document proposes a notational convention to express Concise Binary Object Representation (CBOR) data structures (RFC 7049). Its main goal is to provide an easy and unambiguous way to express structures for protocol messages and data formats that use CBOR or JSON. In network protocol exchanges, it is often useful for one end of a communication to know whether the other end is in an intended operating state. This document provides an architectural overview of the entities involved that make such tests possible through the process of generating, conveying, and evaluating evidentiary Claims. It provides a model that is neutral toward processor architectures, the content of Claims, and protocols. Fraunhofer SIT Linaro arm Intel Huawei Technologies Remote Attestation Procedures (RATS) enable Relying Parties to assess the trustworthiness of a remote Attester and therefore to decide whether or not to engage in secure interactions with it. Evidence about trustworthiness can be rather complex and it is deemed unrealistic that every Relying Party is capable of the appraisal of Evidence. Therefore that burden is typically offloaded to a Verifier. In order to conduct Evidence appraisal, a Verifier requires not only fresh Evidence from an Attester, but also trusted Endorsements and Reference Values from Endorsers and Reference Value Providers, such as manufacturers, distributors, or device owners. This document specifies the information elements for representing Endorsements and Reference Values in CBOR format. IANA IANA Informative References Advanced Micro Devices Inc. Advanced Micro Devices Inc. Advanced Micro Devices Inc. Advanced Micro Devices Inc. Advanced Micro Devices Inc. Red Hound Software Vigil Security, LLC arm arm Trust anchor (TA) stores may be used for several purposes in the Remote Attestation Procedures (RATS) architecture including verifying endorsements, reference values, digital letters of approval, attestations, or public key certificates. This document describes a Concise Reference Integrity Manifest (CoRIM) extension that may be used to convey optionally constrained trust anchor stores containing optionally constrained trust anchors in support of these purposes.

CoRIM Extensions CDDL = (M) .and ({ + any => any }) semver-version-map = { &(version: 0): version-core-text, &(version-scheme: 1): &(semver: 16384) } version-core-text = tstr .regexp "[0-9]+\\.[0-9]+\\.[0-9]+" $$flags-map-extension //= &( sevsnpvm-policy-smt-allowed: -1, sevsnpvm-policy-migration-agent-allowed: -2, sevsnpvm-policy-debug-allowed: -3, sevsnpvm-policy-single-socket-only: -4, sevsnpvm-policy-cxl-allowed: -5, sevsnpvm-policy-mem-aes-256-xts-required: -6, sevsnpvm-policy-rapl-must-be-disabled: -7, sevsnpvm-policy-ciphertext-hiding-must-be-enabled: -8, sevsnpvm-policy-reserved: -47..-9, ) $version-scheme /= &(sevsnpvm-familyimageid-hex: -1) $raw-value-type-choice /= uint $$flags-map-extension //= &( sevsnphost-smt-enabled: -49, sevsnphost-tsme-enabled: -50, sevsnphost-ecc-mem-reported-enabled:-51, sevsnphost-rapl-disabled: -52, sevsnphost-ciphertext-hiding-enabled: -53 sevsnphost-reserved: -112..-49 ) tagged-byte = #6.560(bytes1) tagged-leuint32 = #6.560(bytes4) tagged-leuint64 = #6.560(bytes8) tagged-bytes4 = #6.560(bytes4) tagged-bytes8 = #6.560(bytes8) tagged-bytes32 = #6.560(bytes16) tagged-bytes32 = #6.560(bytes32) tagged-bytes64 = #6.560(bytes64) bytes1 = bytes .size 1 bytes2 = bytes .size 2 bytes4 = bytes .size 4 bytes8 = bytes .size 8 bytes16 = bytes .size 16 bytes32 = bytes .size 32 bytes48 = bytes .size 48 bytes64 = bytes .size 64 svn-type = uint svn = svn-type min-svn = svn-type tagged-svn = #6.552(svn) tagged-min-svn = #6.553(min-svn) svn-type-choice = tagged-svn / tagged-min-svn svn64-type = tagged-svn64 / tagged-min-svn64 tagged-svn64 = #6.552(uint64) tagged-min-svn64 = #6.553(uint64) uint16 = 0..65535 uint32 = 0..4294967295 uint64 = 0..18446744073709551615 ]]>

Contributors arm

yogesh.deshpande@arm.com

Yogesh Deshpande contributed to the data model by providing advice about CoRIM founding principles. Advanced Micro Devices

Bill contributed a review and the OID assignments on behalf of AMD.