Introduction to SGX

Graphene project uses SGX to securely run software. SGX is a complicated topic, which may be hard to learn, because the documentation is scattered through official/reference documentation, blogposts and academic papers. This page is an attempt to curate a dossier of available reading material.

SGX is an umbrella name of technology that comprises several parts:

  • CPU/platform hardware features: the new instruction set, new microarchitecture with the PRM (EPC) memory region and some new MSRs and some new logic in the MMU and so on;
  • the SGX Remote Attestation infrastructure, online services provided by Intel and/or third parties (see DCAP);
  • SDK and assorted software.

SGX is still being developed. The current (March 2020) version of CPU features is referred to as “SGX1” or simply “SGX” and is more or less finalized. All new/changed instructions from original SGX are informally referred to as “SGX2”.

Features which might be considered part of SGX2:

  • EDMM (Enclave Dynamic Memory Management) is part of SGX2
  • FLC (Flexible Launch Control), not strictly part of SGX2, but was not part of original SGX hardware either

As of now there is hardware support (on a limited set of CPUs) for FLC and (on an even more limited set of CPUs) SGX2/EDMM. Most of the literature available (especially introduction-level) concerns original SGX1 only.

Academic Research

Installation Instructions

Todo

TBD

Linux kernel drivers

For historical reasons, there are three SGX drivers currently (January 2021):

  • https://github.com/intel/linux-sgx-driver – old one, does not support DCAP, deprecated

  • https://github.com/intel/SGXDataCenterAttestationPrimitives/tree/master/driver – new one, out-of-tree, supports both non-DCAP software infrastructure (with old EPID remote-attestation technique) and the new DCAP (with new ECDSA and more “normal” PKI infrastructure).

  • SGX support was upstreamed to the Linux mainline starting from 5.11. It currently supports only DCAP attestation. The driver is accessible through /dev/sgx_enclave and /dev/sgx_provision.

    The following udev rules are recommended for users to access the SGX node:

    groupadd -r sgx
    gpasswd -a USERNAME sgx
    groupadd -r sgx_prv
    gpasswd -a USERNAME sgx_prv
    cat > /etc/udev/rules.d/65-graphene-sgx.rules << EOF
      SUBSYSTEM=="misc",KERNEL=="sgx_enclave",MODE="0660",GROUP="sgx"
      SUBSYSTEM=="misc",KERNEL=="sgx_provision",MODE="0660",GROUP="sgx_prv"
      EOF
    udevadm trigger
    

    Also it will not require IAS and kernel maintainers consider non-writable FLC MSRs as non-functional SGX: https://lore.kernel.org/lkml/20191223094614.GB16710@zn.tnic/

The chronicle of kernel patchset:

v1 (2016-04-25)
https://lore.kernel.org/lkml/1461605698-12385-1-git-send-email-jarkko.sakkinen@linux.intel.com/
v2
?
v3
?
v4 (2017-10-16)
https://lore.kernel.org/lkml/20171016191855.16964-1-jarkko.sakkinen@linux.intel.com/
v5 (2017-11-13)
https://lore.kernel.org/lkml/20171113194528.28557-1-jarkko.sakkinen@linux.intel.com/
v6 (2017-11-25)
https://lore.kernel.org/lkml/20171125193132.24321-1-jarkko.sakkinen@linux.intel.com/
v7 (2017-12-07)
https://lore.kernel.org/lkml/20171207015614.7914-1-jarkko.sakkinen@linux.intel.com/
v8 (2017-12-15)
https://lore.kernel.org/lkml/20171215202936.28226-1-jarkko.sakkinen@linux.intel.com/
v9 (2017-12-16)
https://lore.kernel.org/lkml/20171216162200.20243-1-jarkko.sakkinen@linux.intel.com/
v10 (2017-12-24)
https://lore.kernel.org/lkml/20171224195854.2291-1-jarkko.sakkinen@linux.intel.com/
v11 (2018-06-08)
https://lore.kernel.org/lkml/20180608171216.26521-1-jarkko.sakkinen@linux.intel.com/
v12 (2018-07-03)
https://lore.kernel.org/lkml/20180703182118.15024-1-jarkko.sakkinen@linux.intel.com/
v13 (2018-08-27)
https://lore.kernel.org/lkml/20180827185507.17087-1-jarkko.sakkinen@linux.intel.com/
v14 (2018-09-25)
https://lore.kernel.org/lkml/20180925130845.9962-1-jarkko.sakkinen@linux.intel.com/
v15 (2018-11-03)
https://lore.kernel.org/lkml/20181102231320.29164-1-jarkko.sakkinen@linux.intel.com/
v16 (2018-11-06)
https://lore.kernel.org/lkml/20181106134758.10572-1-jarkko.sakkinen@linux.intel.com/
v17 (2018-11-16)
https://lore.kernel.org/lkml/20181116010412.23967-2-jarkko.sakkinen@linux.intel.com/
v18 (2018-12-22)
https://lore.kernel.org/linux-sgx/20181221231134.6011-1-jarkko.sakkinen@linux.intel.com/
v19 (2019-03-20)
https://lore.kernel.org/lkml/20190320162119.4469-1-jarkko.sakkinen@linux.intel.com/
v20 (2019-04-17)
https://lore.kernel.org/lkml/20190417103938.7762-1-jarkko.sakkinen@linux.intel.com/
v21 (2019-07-13)
https://lore.kernel.org/lkml/20190713170804.2340-1-jarkko.sakkinen@linux.intel.com/
v22 (2019-09-03)
https://lore.kernel.org/lkml/20190903142655.21943-1-jarkko.sakkinen@linux.intel.com/
v23 (2019-10-28)
https://lore.kernel.org/lkml/20191028210324.12475-1-jarkko.sakkinen@linux.intel.com/
v24 (2019-11-30)
https://lore.kernel.org/lkml/20191129231326.18076-1-jarkko.sakkinen@linux.intel.com/
v25 (2020-02-04)
https://lore.kernel.org/lkml/20200204060545.31729-1-jarkko.sakkinen@linux.intel.com/
v26 (2020-02-09)
https://lore.kernel.org/lkml/20200209212609.7928-1-jarkko.sakkinen@linux.intel.com/
v27 (2020-02-23)
https://lore.kernel.org/lkml/20200223172559.6912-1-jarkko.sakkinen@linux.intel.com/
v28 (2020-04-04)
https://lore.kernel.org/lkml/20200303233609.713348-1-jarkko.sakkinen@linux.intel.com/
v29 (2020-04-22)
https://lore.kernel.org/lkml/20200421215316.56503-1-jarkko.sakkinen@linux.intel.com/
v30 (2020-05-15)
https://lore.kernel.org/lkml/20200515004410.723949-1-jarkko.sakkinen@linux.intel.com/

SGX terminology

Architectural Enclaves
AE

Architectural Enclaves (AEs) are a set of “system” enclaves concerned with starting and attesting other enclaves. Intel provides reference implementations of these enclaves, though other companies may write their own implementations.

AEP

Todo

TBD

AEX

Todo

TBD

Attestation

Attestation is a mechanism to prove the trustworthiness of the SGX enclave to a local or remote party. More specifically, SGX attestation proves that the enclave runs on a real hardware in an up-to-date TEE with the expected initial state. There are two types of the attestation: Local Attestation and Remote Attestation. For local attestation, the attesting SGX enclave collects attestation evidence in the form of an SGX Report using the EREPORT hardware instruction. For remote attestation, the attesting SGX enclave collects attestation evidence in the form of an SGX Quote using the Quoting Enclave (and the Provisioning Enclave if required). The enclave then may send the collected attestation evidence to the local or remote party, which will verify the evidence and confirm the correctness of the attesting enclave. After this, the local or remote party trusts the enclave and may establish a secure channel with the enclave and send secrets to it.

Data Center Attestation Primitives
DCAP

A software infrastructure provided by Intel as a reference implementation for the new ECDSA/PCS-based remote attestation. Relies on the Flexible Launch Control hardware feature. In principle this is a special version of SDK/PSW that has a reference launch enclave and is backed by the DCAP-enabled SGX driver.

This allows for launching enclaves without Intel’s remote infrastructure. But this requires deployment of own infrastructure, so is operationally more complicated. Therefore it is intended for server environments (where you control all the machines).

See also

Orientation Guide
https://download.01.org/intel-sgx/dcap-1.0.1/docs/Intel_SGX_DCAP_ECDSA_Orientation.pdf
EPID
A way to launch enclaves with Intel’s infrastructure, intended for client machines.
Enclave

Todo

TBD

Enclave Dynamic Memory Management
EDMM
A hardware feature of SGX2, allows dynamic memory allocation, which in turn allows dynamic thread creation.
Enclave Page Cache
EPC

Todo

TBD

Enclave Page Cache Map
EPCM

Todo

TBD

Enhanced Privacy Identification
Enhanced Privacy Identifier
EPID

Todo

short description

Contrary to DCAP, EPID may be understood as “opinionated”, with most moving parts fixed and tied to services provided by Intel. This is intended for client enclaves and deprecated for server environments.

See also

DCAP
A way to launch enclaves without relying on the Intel’s infrastructure.
Flexible Launch Control
FLC

Hardware (CPU) feature that allows substituting Launch Enclave for one not signed by Intel. A change in SGX’s EINIT logic to not require the EINITTOKEN from the Intel-based Launch Enclave. An MSR, which can be locked at boot time, keeps the hash of the public key of the “launching” entity.

With FLC, Launch Enclave can be written by other companies (other than Intel) and must be signed with the key corresponding to the one locked in the MSR (a reference Launch Enclave simply allows all enclaves to run). The MSR can also stay unlocked and then it can be modified at run-time by the VMM or the OS kernel.

Support for FLC can be detected using CPUID instruction, as CPUID.07H:ECX.SGX_LC[bit 30] == 1 (SDM vol. 2A calls this “SGX Launch Control”).

Launch Enclave
LE

Todo

TBD

Local Attestation

In local attestation, the attesting SGX enclave collects attestation evidence in the form of an SGX Report using the EREPORT hardware instruction. This form of attestation is used to send the attestation evidence to a local party (on the same physical machine).

Intel Attestation Service
IAS

Internet service provided by Intel for “old” EPID-based remote attestation. Enclaves send SGX quotes to the client/verifier who will forward them to IAS to check their validity.

See also

PCS
Provisioning Certification Service, another Internet service provided by Intel.
Memory Encryption Engine
MEE

Todo

TBD

OCALL

Todo

TBD

SGX Platform Software
PSW
Software infrastructure provided by Intel with all special Architectural Enclaves (Provisioning Enclave, Quoting Enclave, Launch Enclave). This mainly refers to the “old” EPID/IAS-based remote attestation.
Processor Reserved Memory
PRM

Todo

TBD

Provisioning Enclave
PE

One of the Architectural Enclaves of the Intel SGX software infrastructure. It is part of the SGX Platform Software. The Provisioning Enclave is used in EPID based remote attestation. This enclave communicates with the Intel Provisioning Service (IPS) to perform EPID provisioning. The result of this provisioning procedure is the private EPID key securely accessed by the Provisioning Enclave. This procedure happens only during the first deployment of the SGX machine (or, in rare cases, to provision a new EPID key after TCB upgrade). The main user of the Provisioning Enclave is the Quoting Enclave.

Provisioning Certification Enclave
PCE

One of the Architectural Enclaves of the Intel SGX software infrastructure. It is part of the SGX Platform Software and DCAP. The Provisioning Certification Enclave is used in DCAP based remote attestation. This enclave communicates with the Intel Provisioning Certification Service (PCS) to perform DCAP provisioning. The result of this provisioning procedure is the DCAP/ECDSA attestation collateral (mainly the X.509 certificate chains rooted in a well-known Intel certificate and Certificate Revocation Lists). This procedure happens during the first deployment of the SGX machine and then periodically to refresh the cached attestation collateral. Typically, to reduce the dependency on PCS, a cloud service provider introduces an intermediate caching service (Provisioning Certification Caching Service, or PCCS) that stores all the attestation collateral obtained from Intel. The main user of the Provisioning Certification Enclave is the Quoting Enclave.

Intel Provisioning Service
IPS
Internet service provided by Intel for EPID-based remote attestation. This service provides the corresponding EPID key to the Provisioning Enclave on a remote SGX machine.
Intel Provisioning Certification Service
PCS

New internet service provided by Intel for new ECDSA-based remote attestation. Enclave provider creates its own internal Attestation Service where it caches PKI collateral from Intel’s PCS, and the verifier gets the certificate chain from the enclave provider to check validity.

See also

IAS
Intel Attestation Service, another Internet service.
Quoting Enclave
QE

One of the Architectural Enclaves of the Intel SGX software infrastructure. It is part of the SGX Platform Software. The Quoting Enclave receives an SGX Report and produces a corresponding SGX Quote. The identity of the Quoting Enclave is publicly known (it signer, its measurement and its attributes) and is vetted by public companies such as Intel (in the form of the certificate chain ending in a publicly known root certificate of the company).

Remote Attestation

In remote attestation, the attesting SGX enclave collects attestation evidence in the form of an SGX Quote using the Quoting Enclave (and the Provisioning Enclave if required). This form of attestation is used to send the attestation evidence to a remote party (not on the same physical machine).

Intel SGX Software Development Kit
Intel SGX SDK
SGX SDK
SDK
In the context of SGX, this means a specific piece of software supplied by Intel which helps people write enclaves packed into .so files to be accessible like normal libraries (at least on Linux). Available together with a kernel module and documentation.
SGX Enclave Control Structure
SECS

Todo

TBD

SGX Quote
The SGX quote is the proof of trustworthiness of the enclave and is used during Remote Attestation. The attesting enclave generates the enclave-specific SGX Report, sends the request to the Quoting Enclave using Local Attestation, and the Quoting Enclave returns back the SGX quote with the SGX report embedded in it. The resulting SGX quote contains the enclave’s measurement, attributes and other security-relevant fields, and is tied to the identity of the Quoting Enclave to prove its authenticity. The obtained SGX quote may be later sent to the verifying remote party, which examines the SGX quote and gains trust in the remote enclave.
SGX Report
The SGX report is a data structure that contains the enclave’s measurement, signer identity, attributes and a user-defined 64B string. The SGX report is generated using the EREPORT hardware instruction. It is used during Local Attestation. The SGX report is embedded into the SGX Quote.
SGX2

This refers to all new SGX instructions and other hardware features that were introduced after the release of the original SGX1.

Encompasses at least EDMM, but is still work in progress.

State Save Area
SSA

Todo

TBD

Security Version Number
SVN

Todo

TBD

Trusted Execution Environment
TEE
A Trusted Execution Environment (TEE) is an environment where the code executed and the data accessed are isolated and protected in terms of confidentiality (no one has access to the data except the code running inside the TEE) and integrity (no one can change the code and its behavior).
Trusted Computing Base
TCB

In context of SGX this has the usual meaning: the set of all components that are critical to security. Any vulnerability in TCB compromises security. Any problem outside TCB is not a vulnerability, i.e. should not compromise security.

In context of Graphene there is also a different meaning (Thread Control Block). Those two should not be confused.

Thread Control Structure
TCS

Todo

TBD