About Azure DCasv5/ECasv5-series confidential virtual machines (preview)

Important

Confidential virtual machines (confidential VMs) in Azure confidential computing is currently in PREVIEW. See the Supplemental Terms of Use for Microsoft Azure Previews for legal terms that apply to Azure features that are in beta, preview, or otherwise not yet released into general availability.

Azure confidential computing offers confidential VMs based on AMD processors with SEV-SNP technology. Confidential VMs are for tenants with high security and confidentiality requirements. These VMs provide a strong, hardware-enforced boundary to help meet your security needs. You can use confidential VMs for migrations without making changes to your code, with the platform protecting your VM's state from being read or modified.

Important

Protection levels differ based on your configuration and preferences. For example, Microsoft can own or manage encryption keys for increased convenience at no additional cost.

Benefits

Some of the benefits of confidential VMs include:

  • Robust hardware-based isolation between virtual machines, hypervisor, and host management code.
  • Customizable attestation policies to ensure the host's compliance before deployment.
  • Cloud-based full-disk encryption before the first boot.
  • VM encryption keys that the platform or the customer (optionally) owns and manages.
  • Secure key release with cryptographic binding between the platform's successful attestation and the VM's encryption keys.
  • Dedicated virtual Trusted Platform Module (TPM) instance for attestation and protection of keys and secrets in the virtual machine.
  • Secure boot capability similar to Trusted launch for Azure VMs

Full-disk encryption

Confidential VMs offer a new and enhanced disk encryption scheme. This scheme protects all critical partitions of the disk. It also binds disk encryption keys to the virtual machine's TPM and makes the protected disk content accessible only to the VM. These encryption keys can securely bypass Azure components, including the hypervisor and host operating system. To minimize the attack potential, a dedicated and separate cloud service also encrypts the disk during the initial creation of the VM.

If the compute platform is missing critical settings for your VM's isolation then during boot Azure Attestation will not attest to the platform's health. This will prevent the VM from starting. For example, this scenario happens if you haven't enabled SEV-SNP.

Full-disk encryption is optional, because this process can lengthen the initial VM creation time. You can choose between:

  • A confidential VM with full OS disk encryption before VM deployment that uses platform-managed keys (PMK).
  • A confidential VM without OS disk encryption before VM deployment.

For further integrity and protection, confidential VMs offer Secure Boot by default. With Secure Boot, trusted publishers must sign OS boot components (including the boot loader, kernel, and kernel drivers). All compatible confidential VM images support Secure Boot.

Encryption pricing differences

Confidential VMs use both the OS disk and a small encrypted virtual machine guest state (VMGS) disk of several megabytes. The VMGS disk contains the security state of the VM's components. Some components include the vTPM and UEFI bootloader. The small VMGS disk might incur a monthly storage cost.

Starting in 2022, encrypted OS disks will begin to incur higher costs. This change is because encrypted OS disks use more space, and compression isn't possible. For more information, see the pricing guide for managed disks.

Attestation and TPM

Confidential VMs boot only after successful attestation of the platform's critical components and security settings. The attestation report includes:

  • A signed attestation report issued by AMD SEV-SNP
  • Platform boot settings
  • Platform firmware measurements
  • OS measurements

Confidential VMs feature a virtual TPM (vTPM) for Azure VMs. The vTPM is a virtualized version of a hardware TPM, and complies with the TPM2.0 spec. You can use a vTPM as a dedicated, secure vault for keys and measurements. Confidential VMs have their own dedicated vTPM instance, which runs in a secure environment outside the reach of any VM.

Limitations

The following limitations exist for confidential VMs. For frequently asked questions, see FAQ about confidential VMs with AMD processors.

Size support

Confidential VMs support the following VM sizes:

  • DCasv5-series
  • DCadsv5-series
  • ECasv5-series
  • ECadsv5-series

For more information, see the AMD deployment options.

OS support

Confidential VMs support the following OS options:

  • Ubuntu 20.04 LTS
  • Windows Server 2019
  • Windows Server 2022

Regions

Confidential VMs run on specialized hardware available in specific VM regions.

Pricing

Pricing depends on your confidential VM size. For more information, see the Pricing Calculator.

Feature support

Confidential VMs don't support:

  • Azure Batch
  • Azure Backup
  • Azure Site Recovery
  • Azure Dedicated Host
  • Virtual machine scale set
  • Capturing an image of a VM
  • Azure Compute Gallery
  • Ephemeral OS disks
  • Shared disks
  • Ultra disks
  • Accelerated Networking
  • User-attestable platform reports
  • Live migration
  • Customer-managed keys for OS disk pre-encryption

Next steps