A clear definition of trust for the confidential containers project is needed to ensure the components and architecture deliver the security principles expected for cloud native confidential computing. It provides the solid foundations and unifying security principles against which we can assess architecture and implementation ideas and discussions.
The Trust Modeling for Security Architecture Development article defines Trust Modeling as :
A trust model identifies the specific mechanisms that are necessary to respond to a specific threat profile.
A trust model must include implicit or explicit validation of an entity's identity or the characteristics necessary for a particular event or transaction to occur.
The trust model also helps determine the location and direction of the trust boundaries where a trust boundary describes a location where program data or execution changes its level of "trust", or where two principals with different capabilities exchange data or commands. Specific to Confidential Containers is the trust boundary that corresponds to the boundary of the Trusted Execution Environment (TEE). The TEE side of the trust boundary will be hardened to prevent the violation of the trust boundary.
In order to describe and understand particular threats we need to establish trust boundaries and trust models relating to the key aspects, components and actors involved in Cloud Native Confidential Computing. We explore trust using different orthogonal ways of considering cloud native approaches when they use an underlying TEE technology and identifying where there may be considerations to preserve the value of using a TEE.
Further documentation will highlight specific threat vectors in detail, considering risk, impact, mitigation etc as the project progresses. The Security Assurance section, Page 31, of Cloud Native Computing Foundation (CNCF) Cloud Native Security Paper will guide this more detailed threat vector effort.
Confidential Containers brings confidential computing into a cloud native context and should therefore refer to and build on trust and security models already defined.
For example:
- Confidential Computing Consortium (CCC) published "A Technical Analysis of Confidential Computing" section 5 of which defines the threat model for confidential computing.
- CNCF Security Technical Advisory Group published "Cloud Native Security Whitepaper"
- Kubernetes provides documentation : "Overview of Cloud Native Security"
- Open Web Application Security Project - "Docker Security Threat Modeling"
The commonality between confidential containers project and confidential computing is to reduce the ability for unauthorised access to data and code inside TEEs sufficiently such that this path is not an economically or logically viable attack during execution (5.1 Goal within the CCC publication A Technical Analysis of Confidential Computing).
This means our trust and threat modelling should
- Focus on which aspects of code and data have integrity and/or confidentiality protections.
- Focus on enhancing existing Cloud Native models in the context of exploiting TEEs.
- Consider existing Cloud Native technologies and the role they can play for confidential containers.
- Consider additional technologies to fulfil a role in Cloud Native exploitation of TEEs.
The following items are considered out-of-scope for the trust/threat modelling within confidential containers :
- Vulnerabilities within the application/code which has been requested to run inside a TEE.
- Availability part of the Confidentiality/Integrity/Availability in CIA Triad.
- Software TEEs. At this time we are focused on hardware TEEs.
- Certain security guarantees are defined by the underlying TEE and these may vary between TEEs and generations of the same TEE. We take these guarantees at face value and will only highlight them where they become relevant to the trust model or threats we consider.
In practice, those deploying workloads into TEE environments may have varying levels of trust in the personas who have privileges regarding orchestration or hosting the workload. This trust may be based on factors such as the relationship with the owner or operator of the host, the software and hardware it comprises, and the likelihood of physical, software, or social engineering compromise.
Confidential containers will have specific focus on preventing potential security threats at the TEE boundary and ensure privileges which are accepted within cloud native environment as crossing the boundary are mitigated from threats within the boundary. We cannot allow the security of the TEE to be under control of operations outside the TEE or from areas not trusted by the TEE.