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diff --git a/Documentation/virt/ne_overview.rst b/Documentation/virt/ne_overview.rst new file mode 100644 index 000000000..39b0c8fe2 --- /dev/null +++ b/Documentation/virt/ne_overview.rst @@ -0,0 +1,95 @@ +.. SPDX-License-Identifier: GPL-2.0 + +============== +Nitro Enclaves +============== + +Overview +======== + +Nitro Enclaves (NE) is a new Amazon Elastic Compute Cloud (EC2) capability +that allows customers to carve out isolated compute environments within EC2 +instances [1]. + +For example, an application that processes sensitive data and runs in a VM, +can be separated from other applications running in the same VM. This +application then runs in a separate VM than the primary VM, namely an enclave. + +An enclave runs alongside the VM that spawned it. This setup matches low latency +applications needs. The resources that are allocated for the enclave, such as +memory and CPUs, are carved out of the primary VM. Each enclave is mapped to a +process running in the primary VM, that communicates with the NE driver via an +ioctl interface. + +In this sense, there are two components: + +1. An enclave abstraction process - a user space process running in the primary +VM guest that uses the provided ioctl interface of the NE driver to spawn an +enclave VM (that's 2 below). + +There is a NE emulated PCI device exposed to the primary VM. The driver for this +new PCI device is included in the NE driver. + +The ioctl logic is mapped to PCI device commands e.g. the NE_START_ENCLAVE ioctl +maps to an enclave start PCI command. The PCI device commands are then +translated into actions taken on the hypervisor side; that's the Nitro +hypervisor running on the host where the primary VM is running. The Nitro +hypervisor is based on core KVM technology. + +2. The enclave itself - a VM running on the same host as the primary VM that +spawned it. Memory and CPUs are carved out of the primary VM and are dedicated +for the enclave VM. An enclave does not have persistent storage attached. + +The memory regions carved out of the primary VM and given to an enclave need to +be aligned 2 MiB / 1 GiB physically contiguous memory regions (or multiple of +this size e.g. 8 MiB). The memory can be allocated e.g. by using hugetlbfs from +user space [2][3]. The memory size for an enclave needs to be at least 64 MiB. +The enclave memory and CPUs need to be from the same NUMA node. + +An enclave runs on dedicated cores. CPU 0 and its CPU siblings need to remain +available for the primary VM. A CPU pool has to be set for NE purposes by an +user with admin capability. See the cpu list section from the kernel +documentation [4] for how a CPU pool format looks. + +An enclave communicates with the primary VM via a local communication channel, +using virtio-vsock [5]. The primary VM has virtio-pci vsock emulated device, +while the enclave VM has a virtio-mmio vsock emulated device. The vsock device +uses eventfd for signaling. The enclave VM sees the usual interfaces - local +APIC and IOAPIC - to get interrupts from virtio-vsock device. The virtio-mmio +device is placed in memory below the typical 4 GiB. + +The application that runs in the enclave needs to be packaged in an enclave +image together with the OS ( e.g. kernel, ramdisk, init ) that will run in the +enclave VM. The enclave VM has its own kernel and follows the standard Linux +boot protocol [6]. + +The kernel bzImage, the kernel command line, the ramdisk(s) are part of the +Enclave Image Format (EIF); plus an EIF header including metadata such as magic +number, eif version, image size and CRC. + +Hash values are computed for the entire enclave image (EIF), the kernel and +ramdisk(s). That's used, for example, to check that the enclave image that is +loaded in the enclave VM is the one that was intended to be run. + +These crypto measurements are included in a signed attestation document +generated by the Nitro Hypervisor and further used to prove the identity of the +enclave; KMS is an example of service that NE is integrated with and that checks +the attestation doc. + +The enclave image (EIF) is loaded in the enclave memory at offset 8 MiB. The +init process in the enclave connects to the vsock CID of the primary VM and a +predefined port - 9000 - to send a heartbeat value - 0xb7. This mechanism is +used to check in the primary VM that the enclave has booted. The CID of the +primary VM is 3. + +If the enclave VM crashes or gracefully exits, an interrupt event is received by +the NE driver. This event is sent further to the user space enclave process +running in the primary VM via a poll notification mechanism. Then the user space +enclave process can exit. + +[1] https://aws.amazon.com/ec2/nitro/nitro-enclaves/ +[2] https://www.kernel.org/doc/html/latest/admin-guide/mm/hugetlbpage.html +[3] https://lwn.net/Articles/807108/ +[4] https://www.kernel.org/doc/html/latest/admin-guide/kernel-parameters.html +[5] https://man7.org/linux/man-pages/man7/vsock.7.html +[6] https://www.kernel.org/doc/html/latest/x86/boot.html |