Shielded VMs

Shielded VMs are a feature exclusive to the Datacenter Edition of Windows Server 2016.

As a result of increased virtualization, physical servers that were once secured physically were migrated to Hyper-V hosts that are less secure because they are accessible to fabric administrators. Shielded VMs were introduced to protect tenant workloads from inspection, theft, and tampering as a result of being run on potentially compromised hosts.

A security concept closely associated to shielded VMs is the guarded fabric, which is a collection of nodes cooperating to protect shielded Hyper-V guests. The guarded fabric consists of:

• Host Guardian Service (HGS) utilizes remote attestation to confirm that a node is trusted; if so, it releases a key enabling the shielded VM to be started. HGS is typically a cluster of 3 nodes.
• Guarded hosts: Windows Server 2016 Datacenter edition Hyper-V hosts that can run shielded VMs only if they can prove they are running in a known, trusted state to the Host Guardian Service.
• Shielded VMs

In a production environment, a fabric manager like Virtual Machine Manager would be used to deploy shielded VMs (which are signified by a shield icon).

Shielded VMs must run Windows (8+) or Windows Server (2012+), although Linux shielded VMs are now also supported since version Windows Server version 1709.

Shielded VMs are produced by a three-stage process (VHD -> Shielded template -> Shielded VMs)

1. Preparation: Install and configure an OS onto a virtual disk file
2. Templatization: Convert virtual disk file into a shielded template
3. Provisioning: Create one or more shielded VMs from the shielded template

Configure HGS in its own new forest ^YouTube

Install-WindowsFeature HostGuardianServiceRole -Restart
Install-HgsServer -HgsDomainName 'savtechhgs.net' -SafeModeAdministratorPassword $adminPassword -Restart

Shielding Data is created and owned by tenant VM owners and contains secrets needed to create shielded VMs that must be protected from the fabric admin.

Further reading:

• Intro to shielded VMs
• Create a shielded VM using Powershell
• Linux Shielded VM How To
• Shielded VM Demonstration and Quick Setup
• Guarded Fabric Deployment Guide for Windows Server 2016
• Deploying Shielded VMs and a Guarded Fabric with Windows Server 2016

Attestation

There are two modes of attestation supported by HGS: ^{MS Docs}

• Hardware-trusted attestation
• Remote attestation based on asymmetric key pairs
• Admin-trusted attestation was previously based on guarded host membership in a designated AD DS security group, but is deprecated beginning with Windows Server 2019.

Hardware-trusted attestation mode requires: ^?

• Measured boot: TPMv2 to seal software and hardware configuration details measured at boot
• Code integrity enforcement to strictly define permissible software
• Platform Identity Verification: Active Directory is not sufficient to identify the host. Rather, an identity key rooted in the host TPM is used for identity.

Admin-trusted attestation mode: ^?

• Host identity is verified by checking security group permission
• No Measured Boot or Code Integrity Validation
• Intended to aid transition to Hardware-trusted attestation mode for hosts produced before TPMv2