| Internet-Draft | EAT DA | May 2025 |
| Poirier & Fossati | Expires 23 November 2025 | [Page] |
In confidential computing, device assignment (DA) is the method by which a device (e.g., network adapter, GPU), whether on-chip or behind a PCIe Root Port, is assigned to a Trusted Virtual Machine (TVM). For the TVM to trust the device, the device must provide the TVM with attestation Evidence confirming its identity and the state of its firmware and configuration.¶
This document defines an attestation Evidence format for DA as an EAT (Entity Attestation Token) profile.¶
This note is to be removed before publishing as an RFC.¶
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In confidential computing, device assignment (DA) is the method by which a device (e.g., network adapter, GPU), whether on-chip or behind a PCIe Root Port, is assigned to a Trusted Virtual Machine (TVM). Most confidential computing platforms (e.g., Arm CCA, AMD SEV-SNP, Intel TDX) provide DA capabilities. Such capabilities prevent agents which are untrusted by the TVM (including other TVMs and the host hypervisor) from accessing or controlling a device that has been assigned to the TVM. This includes, for example, protection of device MMIO interfaces and device caches. From a trust perspective, DA allows a device to be included in the TVM's Trusted Computing Base (TCB). For the TVM to trust the device, the device must provide the TVM with attestation Evidence confirming its identity and the state of its firmware and configuration.¶
This document defines an attestation Evidence format for DA as an EAT [RFC9711] profile.¶
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] [RFC8174] when, and only when, they appear in all capitals, as shown here.¶
da-token = {
&(eat_profile: 265) => "tag:linaro.org,2025:device#1.0.0"
&(eat_nonce: 10) => bytes .size 64 ; same as realm nonce
&(eat_submods: 266) => {
+ device-name => $device-claims
}
}
device-name = text .regexp "dev-[A-Za-z0-9]+"
$device-claims /= #6.1000000(spdm-claims)
$device-claims /= #6.1000001(cxl-claims)
$device-claims /= #6.1000002(chi-claims)
¶
spdm-claims = {
&(measurements: 1) => {
+ block-id => spdm-measurement
? "signature" => spdm-measurement-blocks-signature
}
&(certificates: 2) => spdm-certificates
}
block-id = 0..239
¶
spdm-measurement = {
&(component-type: 1) => component-type
measurement
}
measurement //= ( &(digest-measurement: 2) => digest-measurement )
measurement //= ( &(raw-measurement: 3) => raw-measurement )
component-type /= &(immutable-rom: 0)
component-type /= &(mutable-firmware: 1)
component-type /= &(hardware-config: 2)
component-type /= &(firmware-config: 3)
component-type /= &(freeform-measurement-manifest: 4)
component-type /= &(device-mode: 5)
component-type /= &(mutable-firmware-version: 6)
component-type /= &(mutable-firmware-svn: 7)
component-type /= &(hash-extend-measurement: 8)
component-type /= &(informational: 9)
component-type /= &(structured-measurement-manifest: 10)
raw-measurement = bytes
digest-measurement = digest
digest = [
alg: uint / text
val: bytes
]
¶
spdm-certificates = {
device-cert-slot => cert-chain
? aux-cert-slots => cert-chain
}
; ASN.1 DER-encoded certificates concatenated with no intermediate
; padding.
cert-chain = bytes
device-cert-slot = 0
aux-cert-slots = 1..7
¶
=============== NOTE: '\' line wrapping per RFC 8792 ================
da-token = {
&(eat_profile: 265) => "tag:linaro.org,2025:device#1.0.0",
&(eat_nonce: 10) => bytes .size 64,
&(eat_submods: 266) => {+ device-name => $device-claims},
}
device-name = text .regexp "dev-[A-Za-z0-9]+"
$device-claims /= #6.1000000(spdm-claims) / #6.1000001(cxl-claims) \
/ #6.1000002(chi-claims)
spdm-claims = {
&(measurements: 1) => {
+ block-id => spdm-measurement,
? "signature" => spdm-measurement-blocks-signature,
},
&(certificates: 2) => spdm-certificates,
}
block-id = 0 .. 239
spdm-measurement = {
&(component-type: 1) => component-type,
measurement,
}
measurement //= (&(digest-measurement: 2) => digest-measurement // &\
(raw-measurement: 3) => raw-measurement)
component-type /= &(immutable-rom: 0) / &(mutable-firmware: 1) / &(\
hardware-config: 2) / &(firmware-config: 3) / &(freeform-measurement\
-manifest: 4) / &(device-mode: 5) / &(mutable-firmware-version: 6) \
/ &(mutable-firmware-svn: 7) / &(hash-extend-measurement: 8) / &(\
informational: 9) / &(structured-measurement-manifest: 10)
raw-measurement = bytes
digest-measurement = digest
digest = [
alg: uint / text,
val: bytes,
]
spdm-certificates = {
device-cert-slot => cert-chain,
? aux-cert-slots => cert-chain,
}
cert-chain = bytes
device-cert-slot = 0
aux-cert-slots = 1 .. 7
hash-algorithm-type /= &(tpm_alg_sha_256: 0) / &(tpm_alg_sha_384: 2\
) / &(tpm_alg_sha_512: 4) / &(tpm_alg_sha3_256: 8) / &(\
tpm_alg_sha3_384: 16) / &(tpm_alg_sha3_512: 32) / &(tpm_alg_sm3_256\
: 64)
spdm-measurement-blocks-signature = {
&(slot: 1) => 0 .. 7,
&(requester-nonce: 2) => bytes .size 32,
&(responder-nonce: 3) => bytes .size 32,
&(combined-spdm-prefix: 4) => bytes .size 100,
&(IL1: 5) => bytes,
&(base-hash-algo: 6) => hash-algorithm-type,
&(signature: 7) => bytes,
}
cxl-claims = {}
chi-claims = {}
¶
TODO Security¶
TODO IANA CWT allocations¶
=============== NOTE: '\' line wrapping per RFC 8792 ================
{
/ profile / 265: "tag:linaro.org,2025:device#1.0.0",
/ nonce / 10: h'\
f9efc3341597f75f8d94432ad39566a8c5704b2004ba001c094f475bfc057f9f25d7\
aa40cd86cd30ebaae746fb19f008c1e6a1f23ad6a178e18dceda918f7f6e',
/ submods / 266: {
"dev-a": 1000000({
/ measurements / 1: {
1: {
/ component-type / 1: 2, / hardware config /
/ raw-measurement / 3: h'4f6d616861'
}
},
/ certificates / 2: {
/ device certs / 0: h'\
676f616e6e61747261646974696f6e6d6f6e676572'
/ no aux certs /
}
}),
"dev-b": 1000000({
/ measurements / 1: {
0: {
/ component-type / 1: 1, / mutable firmware /
/ digest-measurement / 2: [
/ alg / 1,
/ val / h'6b656e6e656c6c79'
]
},
6: {
/ component-type / 1: 2, / hardware config /
/ digest measurement / 2: [
/ alg / 0,
/ val / h'756e646572637279'
]
}
},
/ certificates / 2: {
/ device certs / 0: h'61746865697A656178696C6C6172',
/ aux certs (slot=2) / 2: h'23451576923AE99106783948598A'
}
})
}
}
¶
TODO acknowledge.¶