Confidential computing: an AWS perspective
Customers around the globe—from governments and highly regulated industries to small businesses and start-ups—trust Amazon Web Services (AWS) with their most sensitive data and applications. At AWS, keeping our customers’ workloads secure and confidential, while helping them meet their privacy and data sovereignty requirements, is our highest priority. Our investments in security technologies and rigorous operational practices meet and exceed even our most demanding customers’ confidential computing and data privacy standards. Over the years, we’ve made many long-term investments in purpose-built technologies and systems to keep raising the bar of security and confidentiality for our customers.
In the past year, there has been an increasing interest in the phrase confidential computing in the industry and in our customer conversations. We’ve observed that this phrase is being applied to various technologies that solve very different problems, leading to confusion about what it actually means. With the mission of innovating on behalf of our customers, we want to offer you our perspective on confidential computing.
At AWS, we define confidential computing as the use of specialized hardware and associated firmware to protect customer code and data during processing from outside access. Confidential computing has two distinct security and privacy dimensions. The most important dimension—the one we hear most often from customers as their key concern—is the protection of customer code and data from the operator of the underlying cloud infrastructure. The second dimension is the ability for customers to divide their own workloads into more-trusted and less-trusted components, or to design a system that allows parties that do not, or cannot, fully trust one another to build systems that work in close cooperation while maintaining confidentiality of each party’s code and data.
In this post, I explain how the AWS Nitro System intrinsically meets the requirements of the first dimension by providing those protections to customers who use Nitro-based Amazon Elastic Compute Cloud (Amazon EC2) instances, without requiring any code or workload changes from the customer side. I also explain how AWS Nitro Enclaves provides a way for customers to use familiar toolsets and programming models to meet the requirements of the second dimension. Before we get to the details, let’s take a closer look at the Nitro System.
What is the Nitro System?
The Nitro System, the underlying platform for all modern Amazon EC2 instances, is a great example of how we have invented and innovated on behalf of our customers to provide additional confidentiality and privacy for their applications. For ten years, we have been reinventing the EC2 virtualization stack by moving more and more virtualization functions to dedicated hardware and firmware, and the Nitro System is a result of this continuous and sustained innovation. The Nitro System is comprised of three main parts: the Nitro Cards, the Nitro Security Chip, and the Nitro Hypervisor. The Nitro Cards are dedicated hardware components with compute capabilities that perform I/O functions, such as the Nitro Card for Amazon Virtual Private Cloud (Amazon VPC), the Nitro Card for Amazon Elastic Block Store (Amazon EBS), and the Nitro Card for Amazon EC2 instance storage.
Nitro Cards—which are designed, built, and tested by Annapurna Labs, our in-house silicon development subsidiary—enable us to move key virtualization functionality off the EC2 servers—the underlying host infrastructure—that’s running EC2 instances. We engineered the Nitro System with a hardware-based root of trust using the Nitro Security Chip, allowing us to cryptographically measure and validate the system. This provides a significantly higher level of trust than can be achieved with traditional hardware or virtualization systems. The Nitro Hypervisor is a lightweight hypervisor that manages memory and CPU allocation, and delivers performances that is indistinguishable from bare metal (we recently compared it against our bare metal instances in the Bare metal performance with the AWS Nitro System post).
The Nitro approach to confidential computing
There are three main types of protection provided by the Nitro System. The first two protections underpin the key dimension of confidential computing—customer protection from the cloud operator and from cloud system software—and the third reinforces the second dimension—division of customer workloads into more-trusted and less-trusted elements.
- Protection from cloud operators: At AWS, we design our systems to ensure workload confidentiality between customers, and also between customers and AWS. We’ve designed the Nitro System to have no operator access. With the Nitro System, there’s no mechanism for any system or person to log in to EC2 servers (the underlying host infrastructure), read the memory of EC2 instances, or access any data stored on instance storage and encrypted EBS volumes. If any AWS operator, including those with the highest privileges, needs to do maintenance work on the EC2 server, they can do so only by using a strictly limited set of authenticated, authorized, and audited administrative APIs. None of these APIs have the ability to access customer data on the EC2 server. Because these technological restrictions are built into the Nitro System itself, no AWS operator can bypass these controls and protections. For additional defense-in-depth against physical attacks at the memory interface level, we offer memory encryption on various EC2 instances. Today, memory encryption is enabled by default on all Graviton2-based instances (T4g, M6g, C6g, C6gn, R6g, X2g), and Intel-based M6i instances, which have Total Memory Encryption (TME). Upcoming EC2 platforms based on the AMD Milan processor will feature Secure Memory Encryption (SME).
- Protection from AWS system software: The unique design of the Nitro System utilizes low-level, hardware-based memory isolation to eliminate direct access to customer memory, as well as to eliminate the need for a hypervisor on bare metal instances.
- For virtualized EC2 instances (as shown in Figure 1), the Nitro Hypervisor coordinates with the underlying hardware-virtualization systems to create virtual machines that are isolated from each other as well as from the hypervisor itself. Network, storage, GPU, and accelerator access use SR-IOV, a technology that allows instances to interact directly with hardware devices using a pass-through connection securely created by the hypervisor. Other EC2 features such as instance snapshots and hibernation are all facilitated by dedicated agents that employ end-to-end memory encryption that is inaccessible to AWS operators.
- For bare metal EC2 instances (as shown in Figure 2), there’s no hypervisor running on the EC2 server, and customers get dedicated and exclusive access to all of the underlying main system board. Bare metal instances are designed for customers who want access to the physical resources for applications that take advantage of low-level hardware features—such as performance counters and Intel® VT—that aren’t always available or fully supported in virtualized environments, and also for applications intended to run directly on the hardware or licensed and supported for use in non-virtualized environments. Bare metal instances feature the same storage, networking, and other EC2 capabilities as virtualized instances because the Nitro System implements all of the system functions normally provided by the virtualization layer in an isolated and independent manner using dedicated hardware and purpose-built system firmware. We used the very same technology to create Amazon EC2 Mac instances. Because the Nitro System operates over an independent bus, we can attach Nitro cards directly to Apple’s Mac mini hardware without any other physical modifications.
- Protection of sensitive computing and data elements from customers’ own operators and software: Nitro Enclaves provides the second dimension of confidential computing. Nitro Enclaves is a hardened and highly-isolated compute environment that’s launched from, and attached to, a customer’s EC2 instance. By default, there’s no ability for any user (even a root or admin user) or software running on the customer’s EC2 instance to have interactive access to the enclave. Nitro Enclaves has cryptographic attestation capabilities that allow customers to verify that all of the software deployed to their enclave has been validated and hasn’t been tampered with. A Nitro enclave has the same level of protection from the cloud operator as a normal Nitro-based EC2 instance, but adds the capability for customers to divide their own systems into components with different levels of trust. A Nitro enclave provides a means of protecting particularly sensitive elements of customer code and data not just from AWS operators but also from the customer’s own operators and other software.As the main goal of Nitro Enclaves is to protect against the customers’ own users and software on their EC2 instances, a Nitro enclave considers the EC2 instance to reside outside of its trust boundary. Therefore, a Nitro enclave shares no memory or CPU cores with the customer instance. To significantly reduce the attack surface area, a Nitro enclave also has no IP networking and offers no persistent storage. We designed Nitro Enclaves to be a platform that is highly accessible to all developers without the need to have advanced cryptography knowledge or CPU micro-architectural expertise, so that these developers can quickly and easily build applications to process sensitive data. At the same time, we focused on creating a familiar developer experience so that developing the trusted code that runs in a Nitro enclave is as easy as writing code for any Linux environment.
To summarize, the Nitro System’s unique approach to virtualization and isolation enables our customers to secure and isolate sensitive data processing from AWS operators and software at all times. It provides the most important dimension of confidential computing as an intrinsic, on-by-default, set of protections from the system software and cloud operators, and optionally via Nitro Enclaves even from customers’ own software and operators.
As mentioned earlier, the Nitro System represents our almost decade-long commitment to raising the bar for security and confidentiality for compute workloads in the cloud. It has allowed us to do more for our customers than is possible with off-the-shelf technology and hardware. But we’re not stopping here, and will continue to add more confidential computing capabilities in the coming months.
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