ARM CCA

ARM CCA introduces dynamically created address spaces called Realms that are isolated from the hypervisor and other virtual machines. Unlike traditional VMs, a Realm's memory is encrypted and integrity-protected at the hardware level. The Realm Management Monitor (RMM) is a small, formally verified firmware component that manages Realm transitions, ensuring the hypervisor cannot access Realm memory even during context switches. This creates a minimal Trusted Computing Base (TCB) that excludes the entire host OS and hypervisor stack.

ARM CCA manages memory at the granule level, the same unit used by the Memory Management Unit (MMU). The Granule Protection Table (GPT) is a hardware-walked structure that assigns each granule a state: Non-Secure, Secure, Realm, or Root. This allows the architecture to dynamically transition memory pages between the hypervisor and a Realm while enforcing strict access controls. A granule assigned to a Realm cannot be read or written by the hypervisor, preventing data exfiltration even by a compromised host.

ARM CCA is designed to protect Confidential AI workloads, including model inference and training. By placing a machine learning model and its input data inside a Realm, both the model's intellectual property and the user's sensitive data remain confidential even from the cloud provider. This enables private inference scenarios where:

• Model weights are never exposed to the host
• Input data is encrypted until inside the Realm
• Attestation verifies the inference environment before execution This is critical for regulated industries processing personally identifiable information (PII) or protected health information (PHI).

ARM CCA supports a Delegated Realm model where the initial measurement and attestation of a Realm can be delegated to a trusted service provider. This allows cloud operators to manage the lifecycle of Realms without being able to inspect their contents. The Realm Service Manager (RSM) concept separates the administrative plane from the data plane, enabling scalable confidential computing services where the infrastructure owner handles scheduling and resource allocation while remaining cryptographically excluded from the workload's data.

The Realm Management Monitor (RMM) is the critical firmware component that enforces isolation between Realms and the hypervisor. ARM has subjected the RMM specification to formal mathematical verification to prove its security properties. This verification ensures:

• No information leakage between Realm and non-Realm worlds
• Correct handling of all state transitions
• Absence of undefined behavior in the interface This rigorous approach reduces the attack surface to a minimal, auditable codebase, significantly raising the bar for potential attackers.

The overarching hardware-based security paradigm that protects data in use by performing computation within a hardware-enforced Trusted Execution Environment. ARM CCA is a specific architectural implementation of confidential computing that extends protection boundaries to entire virtual machines through Realms, shielding workloads from the hypervisor, host OS, and cloud provider.

The cryptographic process by which an ARM CCA Realm proves its identity, integrity, and security posture to a remote relying party before secrets are provisioned. CCA uses the Hardware Enforced Security (HES) component and CCA Token format, enabling verifiers to cryptographically confirm that a Realm is genuine and running unmodified code on authentic ARM hardware.

A full virtual machine instance running inside a hardware-backed TEE, encrypting its entire memory space. ARM CCA Realms are a type of Confidential VM that provide:

• Memory encryption transparent to the guest OS
• Hypervisor exclusion from the Trusted Computing Base
• Dynamic memory assignment through Granule Protection Tables
• Lift-and-shift migration without application modification

The set of all hardware, firmware, and software components critical to a system's security. ARM CCA dramatically reduces the TCB by:

• Removing the hypervisor and host OS from the trust boundary
• Limiting trusted firmware to the Monitor at EL3 and the RMM at EL2
• Excluding the Realm owner's management software from the guest's TCB
• A smaller TCB means fewer attack surfaces and easier formal verification