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Arm Confidential Compute Architecture (CCA) is a platform design for isolating code and data while they are being processed. Its protected execution environments are called Realms. CCA combines Armv9-A hardware mechanisms with monitor firmware, a Realm Management Monitor (RMM), and host software; it is not a standalone product or proof that a particular server or cloud service currently offers confidential-computing Realms.
What is Arm CCA?
Confidential computing protects information during use, not only when it is stored or sent over a network. Arm CCA adds a Realm execution environment to the Arm platform so a workload can run separately from ordinary host software, including a privileged hypervisor.
Arm describes CCA as a complete hardware-and-software architecture. The Realm Management Extension (RME) is the principal Armv9-A architectural feature that provides the hardware foundation. Firmware and software components then establish, manage and attest Realm execution.
Arm’s architecture guide is Version 4.0, with a release-history update dated 19 March 2025. The CCA software-stack guide lists Version 3.0, issue 0200-06, a minor update dated 30 June 2025. Those are documentation versions, not launch dates or evidence of a commercial server release.
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What is a Realm in Arm CCA?
A Realm is CCA’s protected execution environment for a guest operating system, application and its working data. In the intended isolation model, privileged host software manages the machine but cannot read the Realm’s protected contents.
The boundary is deliberately narrower than “the entire computer is trusted.” The host still starts and schedules the Realm and controls resources such as memory allocation, processor time and device access. Platform firmware, hardware, devices, accelerators and operational procedures remain relevant trust assumptions unless a particular implementation protects them separately.
The execution worlds
| Component or world | Primary role | What it means for trust |
|---|---|---|
| Normal world | Runs the host operating system, hypervisor and ordinary applications. | The hypervisor can set policy and allocate resources, but it is outside the Realm’s protected workload boundary. |
| Secure world | Runs security services in the conventional Arm TrustZone model. | Remains a separate security domain; CCA does not replace every secure-world function. |
| Realm world | Runs the confidential guest workload. | Designed to keep Realm code and data inaccessible to untrusted host software. |
| Root world | Runs monitor software that mediates transitions between worlds. | Forms part of the platform’s root of trust and must be implemented and maintained correctly. |
How RME, the RMM and the hypervisor fit together
RME and CCA are related but not interchangeable terms. RME supplies the architectural hardware mechanisms; CCA adds the firmware and software needed to turn those mechanisms into a usable Realm platform.
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RME: the hardware foundation
RME extends Armv9-A so memory and execution state can be assigned to Realm or other security states. It establishes the hardware-enforced separation on which CCA relies.
Monitor firmware: transitions and root-of-trust work
Arm’s CCA stack places the Trusted Firmware-A (TF-A) Monitor in the CPU root of trust. It mediates transitions among the Normal, Secure and Realm worlds and performs operations that must not be delegated to an untrusted host.
RMM (including TF-RMM): Realm management
The Realm Management Monitor handles Realm communication and context or mechanism operations. Arm’s reference implementation is known as TF-RMM, and the CCA page places it at Realm EL2.
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Hypervisor: policy and resources
The host hypervisor remains responsible for policy decisions, such as how much memory or processor time a Realm receives and when it runs. It asks the trusted monitor and RMM to perform Realm operations, but it is not supposed to implement the protected mechanisms itself.
How CCA protects data in use
- Create an isolated Realm. Platform firmware and the RMM establish the Realm’s execution context and memory ownership using RME-backed mechanisms.
- Load the guest and workload. A guest Linux kernel and its application execute inside the Realm rather than in the host’s ordinary address space.
- Keep host access outside the protected contents. The host can schedule the Realm and provide resources, but the design prevents it from directly reading protected Realm memory or execution state.
- Mediate communication. Calls between the Realm and host are handled through defined interfaces and monitor/RMM mechanisms instead of unrestricted shared access.
- Measure initial state for verification. The Realm’s initial software state and relevant platform state can be represented in attestation evidence.
This model reduces the trust placed in a cloud operator’s host kernel or hypervisor. It does not make an application automatically secure: vulnerabilities inside the guest, unsafe inputs, compromised dependencies, malicious devices or flawed platform firmware can still matter.
What CCA attestation proves—and what it does not
Attestation gives a workload owner evidence with which to evaluate the Realm and the platform on which it runs. A verifier can use that evidence in a policy decision, such as releasing a decryption key only to an expected initial software state.
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Attestation is not a universal application-safety certificate. It does not, by itself, prove that the application has no vulnerabilities, that every attached device is trustworthy, or that a cloud provider offers CCA Realms. The verifier must define acceptable measurements, validate the evidence and decide what to trust.
How to run an application in an Arm CCA Realm
Arm’s learning material provides a developer-oriented simulation path. It uses a prebuilt Docker container to create a Realm, boot a guest Linux kernel with a simple application, and obtain a CCA attestation token.
- Install the container tooling required by Arm’s tutorial and obtain the prebuilt CCA development container.
- Start the container and follow the tutorial’s setup to launch the simulated platform.
- Create a Realm and boot the supplied guest Linux kernel.
- Run the example application inside that guest, confirming that execution occurs in the Realm environment.
- Request the Realm’s attestation token and inspect the evidence for the initial Realm and platform state.
- Adapt the example to your own guest image or verifier policy only after understanding the tutorial’s measurement and key-release flow.
This exercise demonstrates an integration and verification workflow. It is a simulation/tutorial experience, not evidence that a named Arm server model, cloud region or production service is commercially available.
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CCA compared with another confidential-computing implementation
Architecture names alone do not establish which technology is safer or more suitable. Compare implementations along the same operational axes:
| Evaluation axis | Questions to ask |
|---|---|
| Trust boundary | Which host, firmware, device, accelerator and operator layers remain outside the protected environment? |
| Attestation | What is measured, who signs it, how is it verified, and how are keys released after verification? |
| Workload packaging | Can existing virtual machines or containers run unchanged? How are images measured, updated and migrated? |
| Platform prerequisites | Which processor features, firmware versions, monitor and RMM implementations are required? |
| Devices and accelerators | Can protected workloads use network, storage, GPUs or other accelerators without expanding the trust boundary? |
| Availability | Which specific server SKU, provider, region and product plan supports the feature, and under what terms? |
What is—and is not—established about availability
Arm’s current CCA material discusses cloud, edge, confidential-AI and accelerator scenarios as intended use cases. The reviewed architecture and learning documents do not identify a current production server SKU, cloud provider, region, price or accelerator model that offers CCA Realms. Any deployment decision therefore requires separate, current evidence from the relevant hardware or service provider.
In practical terms, CCA is best understood today as an architecture and development path: RME-backed hardware mechanisms, trusted monitor and RMM software, Realm workloads, and attestation-based verification. A production claim requires all of those pieces, plus a platform operator that exposes and supports them.
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