Container Measurement Specification

1 Scope and Introduction

1.1 Scope

This specification is a companion to the “TCG PC Platform Firmware Profile Specification” and the “Canonical Event Log Format”, which aims to expand integrity measurement and chain of trust to the container application level and specifies integrity measurement for a container. The specification explains the concepts and usage of container measurement, the focus includes container runtime measurement and container runtime caller measurement. The scope does not include boot firmware measurement, boot loader measurement, and operating system measurement, but it requires the boot process to be measured to build a chain of trust for container measurement. This specification defines the chain of trust for containers, container measurement register, and container event log.

2 Container Measurement

2.1 Measurement Process

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2.2 Chain of Trust for Container

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2.3 Measuring Container

OCI develops the specifications for standard container image format and container runtime, both container image and container runtime SHALL be measured. The container runtime caller also SHALL be measured.

2.3.1 Measuring Container Image

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2.3.2 Measuring Container Runtime

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2.3.3 Measuring Container Runtime Caller

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3 Container Measurement Register

TPM PCR 0~15 is defined and used as firmware and system OS measurement in UAPI Group Specification Linux TPM PCR Registry, PCR 11 and 15 are used by multiple components and there are not conflicting uses, in container measurement, these two registers can be reused to extend the measurement of container runtime and application measurement inside a container.

PCR Index	Usage
11	The measurement of container runtime caller
15	Application inside container

4 Container Measurement Event Log

4.1 Container Measurement Event Types

The CEL Event Content field is encoded in a TLV includes CEL, PCCLIENT_STD, IMA_TEMPLATE, IMA_TLV. Add a new TLV format CM_TLV for container integrity measurement layer.

<CONTENT> TLV
T	CEL	4	Management Content Type
	PCCLIENT_STD	5	PC Client WG defined encapsulated structure
	IMA_TEMPLATE	7	Linux IMA_TEMPLATE format
	IMA_TLV	8	IMA directly stored in CEL-TLV format
	CM_TLV	9	Container Measurement TLV format
L			The length of the value (V) network byte order
V			The value, according to the type (T)

4.1.1 CM_TLV Content Layer

CM_TLV
T	CM_TLV_CONTENT_ VERSION	Version of container runtime and container runtime callers
	CM_TLV_CONTENT_CONFIG	Configuration of container image and container runtime and container runtime callers
	CM_TLV_CONTENT_LAYER	The layer of the container image
	CM_TLV_CONTENT_PROCESS	Process binaries of container runtime and container runtime callers
	CM_TLV_CONTENT_CONTAINER	The status of container lifecycle
	CM_TLV_CONTENT_POD	The status of one or more containers that run applications
	CM_TLV_CONTENT_CLUSTER	The status of the cluster
L		The length of the value (V)
V		The value (V) containing data of the type (T)

Reference

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