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44 lines
4.2 KiB
Markdown
44 lines
4.2 KiB
Markdown
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# Feature status of clouds
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What works on which cloud? Currently, Confidential VMs (CVMs) are available in varying quality on the different clouds and software stacks.
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For Constellation, the ideal environment provides the following:
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1. Ability to run arbitrary software and images inside CVMs
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2. CVMs based on AMD SEV-SNP (available in EPYC CPUs since the Milan generation) or, in the future, Intel TDX (available in Xeon CPUs from the Sapphire Rapids generation onward)
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3. Ability for CVM guests to obtain raw attestation statements directly from the CPU, ideally via a TPM-like interface
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4. Reviewable, open-source firmware inside CVMs
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(1) is a functional must-have. (2)--(4) are required for remote attestation that fully keeps the infrastructure/cloud out. Constellation can work without them or with approximations, but won't protect against certain privileged attackers anymore.
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The following table summarizes the state of features for different infrastructures as of September 2022.
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| **Feature** | **Azure** | **GCP** | **AWS** | **OpenStack (Yoga)** |
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|-------------------------------|-----------|---------|---------|----------------------|
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| **1. Custom images** | Yes | Yes | No | Yes |
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| **2. SEV-SNP or TDX** | Yes | No | No | Depends on kernel/HV |
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| **3. Raw guest attestation** | Yes | No | No | Depends on kernel/HV |
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| **4. Reviewable firmware** | No* | No | No | Depends on kernel/HV |
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## Microsoft Azure
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With its [CVM offering](https://docs.microsoft.com/en-us/azure/confidential-computing/confidential-vm-overview), Azure provides the best foundations for Constellation. Regarding (3), Azure provides direct access to remote-attestation statements. However, regarding (4), the standard CVMs still include closed-source firmware running in VM Privilege Level (VMPL) 0. This firmware is signed by Azure. The signature is reflected in the remote-attestation statements of CVMs. Thus, the Azure closed-source firmware becomes part of Constellation's trusted computing base (TCB).
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Recently, Azure [announced](https://techcommunity.microsoft.com/t5/azure-confidential-computing/azure-confidential-vms-using-sev-snp-dcasv5-ecasv5-are-now/ba-p/3573747) the *limited preview* of CVMs with customizable firmware. With this CVM type, (4) switches from *No* to *Yes*. Constellation will support customizable firmware on Azure in the future.
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## Google Cloud Platform (GCP)
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The [CVMs available in GCP](https://cloud.google.com/compute/confidential-vm/docs/create-confidential-vm-instance) are based on AMD SEV but don't have SNP features enabled. This impacts attestation capabilities. Currently, GCP doesn't offer CVM-based attestation at all. Instead, GCP provides attestation statements based on its regular [vTPM](https://cloud.google.com/blog/products/identity-security/virtual-trusted-platform-module-for-shielded-vms-security-in-plaintext), which is managed by the hypervisor. On GCP, the hypervisor is thus currently part of Constellation's TCB.
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## Amazon Web Services (AWS)
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AWS currently doesn't offer CVMs. AWS proprietary Nitro Enclaves offer some related features, but [are explicitly not designed to keep AWS itself out](https://aws.amazon.com/blogs/security/confidential-computing-an-aws-perspective/). An experimental version of Constellation exists that runs on Nitro Enclaves.
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## OpenStack
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OpenStack is an open-source cloud and infrastructure management software. It's used by many smaller CSPs and datacenters. In the latest *Yoga* version, OpenStack has basic support for CVMs. However, much depends on the employed kernel and hypervisor. Features (2)--(4) are likely to be a *Yes* with Linux kernel version 6.2. Thus, going forward, OpenStack on corresponding AMD or Intel hardware will be a viable underpinning for Constellation.
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## Conclusion
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The different clouds and software like the Linux kernel and OpenStack are in the process of building out their support for state-of-the-art CVMs. Azure has already most features in place. For Constellation, the status quo means that the TCB has different shapes on different infrastructures. With broad SEV-SNP support coming to the Linux kernel, we soon expect a normalization of features across infrastructures.
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