Azure DCasv5/ECasv5-series confidential virtual machines FAQ

This article provides answers to some of the most common questions about confidential VMs.

What are confidential VMs?

Confidential VMs are IaaS VMs for tenants with especially high security and confidentiality requirements. Confidential VMs offer access to the following technologies and benefits:

  • Encryption for "data in use”, including the processor state and the virtual machine’s memory. Keys are generated by the processor and never leave it.
  • Host attestation to verify the full health and compliance of the server before initializing a confidential VM.
  • Encryption of "data at rest." A Hardware Security Module (HSM) can be used to guard the keys, which the tenant exclusively owns.
  • New UEFI boot architecture supporting the guest OS for enhanced security settings and capabilities.
  • A dedicated virtual instance of a Trusted Platform Module (TPM). Certifies the health of the VM and provides hardened key management functions. Supports use cases such as BitLocker.

Why should I use confidential VMs?

Confidential VMs address customer concerns about moving sensitive workloads off-premise into the cloud. Confidential VMs provide significantly elevated protections for customer data from the underlying infrastructure and cloud operators. Unlike other approaches and solutions, you don't have to adapt your existing workloads to fit the platform's technical needs.

What are AMD SEV-SNP technologies and how do they relate to Azure confidential VMs?

AMD Secure Encrypted Virtualization-Secure Nested Paging (SEV-SNP) technology offers multiple protections. For example, memory encryption, unique CPU keys, encryption for the processor register state, strong integrity protection, firmware rollback prevention, side channel hardening, and restrictions on interrupt and exceptions behavior. Collectively, AMD SEV technologies harden guest protections to deny hypervisor and other host management code access to VM memory and state. Confidential VMs combine AMD SEV-SNP with Azure technologies such as full-disk encryption and Azure Key Vault Managed HSM. You can encrypt data in use, in transit, and at rest with keys that you control. With built-in Azure Attestation capabilities, you can independently establish trust in the security health and underlying infrastructure of your confidential VMs.

How do Azure confidential VMs (DCasv5/ECasv5) offer better protection against threats originating from both within and outside Azure cloud infrastructure?

Azure VMs already offer industry leading security and protection against other tenants and malicious intruders. Azure confidential VMs augment these protections by using hardware-based TEEs (Trusted Execution Environment) which leverage AMD’s SEV-SNP to cryptographically isolate and protect your data confidentiality and integrity even when they are in use. This means not host admins, or services (including the Azure hypervisor) can directly view or modify the memory or CPU state of your VM. Moreover, with full attestation capability, full OS disk encryption and hardeware-protected virtual Trusted Platform Modules, confidential VM persistent state is protected such that neither your private keys, nor are the contents of your memory are ever exposed to the hosting environment.

Are the virtual disks attached to confidential VMs automatically protected?

Currently OS disks for confidential VMs can be encrypted and secured. For additional security, you can enable guest level encryption (such as BitLocker or dm-crypt) for all data drives.

Does memory written to the Windows swap file (pagefile.sys) get protected by the TEE?

Yes, but only if the pagefile.sys is located on the encrypted OS disk. On confidential VMs with a temp disk, the pagefile.sys file can be moved to the encrypted OS Tips for moving pagefile.sys to the c:\ drive.

How can I deploy Azure confidential VMs?

Here are some ways you can deploy a confidential VM on AMD processors:

Can I perform attestation for my confidential VMs?

Azure confidential VMs undergo attestation as part of their boot phase. This process is opaque to the user and takes place in the cloud operating system in conjunction with the Microsoft Azure Attestation and Azure Key Vault services. Confidential VMs also allow users to perform independent attestation for their confidential VMs. This attestation happens using new tooling called Azure confidential VM Guest Attestation. Guest attestation allows customers to attest that their confidential VMs are running on AMD processors with SEV-SNP enabled.

Do all OS images work with confidential VMs?

To run on a confidential VM, OS images must meet certain security and compatibility requirements. This allows confidential VMs to be securely mounted, attested to, and isolated from the underlying cloud infrastructure. In the future we plan to provide guidance on how to take a custom Linux build and apply a set of open-source patches to qualify it as a confidential VM image.

Can I customize one of the available confidential VM images?

Yes. You can use Azure Compute Gallery to modify a confidential VM image, such as by installing applications. Then, you can deploy confidential VMs based on your modified image.

Do I have to use the full-disk encryption scheme? Can I use a standard scheme instead?

The optional full-disk encryption scheme is Azure's most secure and meets the Confidential Computing principles. However, you can also use other disk encryption schemes along with or instead of full-disk encryption. If you use multiple disk encryption schemes, double encryption might negatively affect performance.

Since Azure confidential VMs support virtual TPM, can I seal secrets/keys to my confidential VM virtual TPM?

Each Azure confidential VM has its own virtual TPM, where customers can seal their secrets/keys. It is recommended for customers to verify vTPM status (via TPM.msc for Windows VMs). If status is not ready for use, we recommend that you reboot your VMs before sealing secrets/keys to vTPM.

Can I enable or disable the new full-disk encryption scheme after VM creation?

No. After you've created a confidential VM, you can't deactivate or reactivate full-disk encryption. Create a new confidential VM instead.

Can I convert a non-confidential VM into a confidential VM?

No. For security reasons, you must create a confidential VM as such from the start.

Why can't I find DCasv5 or ECasv5 VMs in the Azure portal size selector?

Make sure you've selected an available region for confidential VMs. Also make sure to select clear all filters in the size selector.

Can I enable Azure Accelerated Networking on confidential VMs?

No. Confidential VMs don't support Accelerated Networking. You can't enable Accelerated Networking for any confidential VM deployment, or any Azure Kubernetes Service cluster deployment that runs on Confidential Computing.

What does this error mean? "Operation couldn't be completed as it results in exceeding approved standard DCasV5/ECasv5 Family Cores Quota"

You might receive the error Operation could not be completed as it results in exceeding approved standard DCasv5/ECasv5 Family Cores Quota. This Azure Resource Manager template (ARM template) error means the deployment failed because of a lack of Azure compute cores. Azure free trial subscriptions don't have a large enough core quota for confidential VMs. Create a support request to increase your quota.

What's the difference between DCasv5-series and ECasv5-series VMs?

ECasv5-series are memory-optimized VM sizes, which offer a higher memory-to-CPU ratio. These sizes are especially well-suited for relational database servers, medium to large caches, and in-memory analytics.

Are DCasv5/ECasv5 VMs available globally?

No. At this time, these VMs are only available in select regions. For a current list of available regions, see VM products by region.

What happens if I need Microsoft to help me service or access data on my confidential VM?

Azure doesn't have operating procedures for granting confidential VM access to its employees, even if a customer authorizes the access. As a result, various recovery and support scenarios aren't available for confidential VMs.

Do confidential VMs support virtualization, such as Azure VMware Solution?

No, confidential VMs don't currently support nested virtualization, such as the ability to run a hypervisor inside a VM.

Is there an extra cost for using confidential VMs?

Billing for confidential VMs depends on your usage and storage, and the size and region of the VM. Confidential VMs are available in dedicated sizes, so prices might differ from general-purpose VMs. Confidential VMs use a small encrypted virtual machine guest state (VMGS) disk of several megabytes. VMGS encapsulates the VM security state of components such the vTPM and UEFI bootloader. This disk might result in a monthly storage fee. Also, if you choose to enable the optional full-disk encryption, encrypted OS disks will incur higher costs. This change is because encrypted OS disks use more space, and compression isn't possible. For more information on storage fees, see the pricing guide for managed disks. Lastly, for some high security and privacy settings, you might choose to create linked resources, such as a Managed HSM Pool. Azure bills such resources separately from the confidential VM costs.