101 lines
4.9 KiB
ReStructuredText
101 lines
4.9 KiB
ReStructuredText
.. SPDX-License-Identifier: GPL-2.0
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==============
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Nitro Enclaves
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==============
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Overview
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========
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Nitro Enclaves (NE) is a new Amazon Elastic Compute Cloud (EC2) capability
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that allows customers to carve out isolated compute environments within EC2
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instances [1].
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For example, an application that processes sensitive data and runs in a VM,
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can be separated from other applications running in the same VM. This
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application then runs in a separate VM than the primary VM, namely an enclave.
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It runs alongside the VM that spawned it. This setup matches low latency
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applications needs.
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The current supported architectures for the NE kernel driver, available in the
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upstream Linux kernel, are x86 and ARM64.
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The resources that are allocated for the enclave, such as memory and CPUs, are
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carved out of the primary VM. Each enclave is mapped to a process running in the
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primary VM, that communicates with the NE kernel driver via an ioctl interface.
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In this sense, there are two components:
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1. An enclave abstraction process - a user space process running in the primary
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VM guest that uses the provided ioctl interface of the NE driver to spawn an
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enclave VM (that's 2 below).
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There is a NE emulated PCI device exposed to the primary VM. The driver for this
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new PCI device is included in the NE driver.
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The ioctl logic is mapped to PCI device commands e.g. the NE_START_ENCLAVE ioctl
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maps to an enclave start PCI command. The PCI device commands are then
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translated into actions taken on the hypervisor side; that's the Nitro
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hypervisor running on the host where the primary VM is running. The Nitro
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hypervisor is based on core KVM technology.
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2. The enclave itself - a VM running on the same host as the primary VM that
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spawned it. Memory and CPUs are carved out of the primary VM and are dedicated
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for the enclave VM. An enclave does not have persistent storage attached.
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The memory regions carved out of the primary VM and given to an enclave need to
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be aligned 2 MiB / 1 GiB physically contiguous memory regions (or multiple of
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this size e.g. 8 MiB). The memory can be allocated e.g. by using hugetlbfs from
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user space [2][3][7]. The memory size for an enclave needs to be at least
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64 MiB. The enclave memory and CPUs need to be from the same NUMA node.
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An enclave runs on dedicated cores. CPU 0 and its CPU siblings need to remain
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available for the primary VM. A CPU pool has to be set for NE purposes by an
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user with admin capability. See the cpu list section from the kernel
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documentation [4] for how a CPU pool format looks.
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An enclave communicates with the primary VM via a local communication channel,
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using virtio-vsock [5]. The primary VM has virtio-pci vsock emulated device,
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while the enclave VM has a virtio-mmio vsock emulated device. The vsock device
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uses eventfd for signaling. The enclave VM sees the usual interfaces - local
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APIC and IOAPIC - to get interrupts from virtio-vsock device. The virtio-mmio
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device is placed in memory below the typical 4 GiB.
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The application that runs in the enclave needs to be packaged in an enclave
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image together with the OS ( e.g. kernel, ramdisk, init ) that will run in the
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enclave VM. The enclave VM has its own kernel and follows the standard Linux
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boot protocol [6][8].
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The kernel bzImage, the kernel command line, the ramdisk(s) are part of the
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Enclave Image Format (EIF); plus an EIF header including metadata such as magic
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number, eif version, image size and CRC.
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Hash values are computed for the entire enclave image (EIF), the kernel and
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ramdisk(s). That's used, for example, to check that the enclave image that is
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loaded in the enclave VM is the one that was intended to be run.
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These crypto measurements are included in a signed attestation document
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generated by the Nitro Hypervisor and further used to prove the identity of the
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enclave; KMS is an example of service that NE is integrated with and that checks
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the attestation doc.
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The enclave image (EIF) is loaded in the enclave memory at offset 8 MiB. The
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init process in the enclave connects to the vsock CID of the primary VM and a
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predefined port - 9000 - to send a heartbeat value - 0xb7. This mechanism is
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used to check in the primary VM that the enclave has booted. The CID of the
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primary VM is 3.
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If the enclave VM crashes or gracefully exits, an interrupt event is received by
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the NE driver. This event is sent further to the user space enclave process
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running in the primary VM via a poll notification mechanism. Then the user space
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enclave process can exit.
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[1] https://aws.amazon.com/ec2/nitro/nitro-enclaves/
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[2] https://www.kernel.org/doc/html/latest/admin-guide/mm/hugetlbpage.html
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[3] https://lwn.net/Articles/807108/
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[4] https://www.kernel.org/doc/html/latest/admin-guide/kernel-parameters.html
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[5] https://man7.org/linux/man-pages/man7/vsock.7.html
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[6] https://www.kernel.org/doc/html/latest/x86/boot.html
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[7] https://www.kernel.org/doc/html/latest/arm64/hugetlbpage.html
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[8] https://www.kernel.org/doc/html/latest/arm64/booting.html
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