Light-Weight Contexts: An OS Abstraction for Safety and Performance


James Litton, University of Maryland and Max Planck Institute for Software Systems (MPI-SWS); Anjo Vahldiek-Oberwagner, Eslam Elnikety, and Deepak Garg, Max Planck Institute for Software Systems (MPI-SWS); Bobby Bhattacharjee, University of Maryland; Peter Druschel, Max Planck Institute for Software Systems (MPI-SWS)


We introduce a new OS abstraction—light-weight contexts (lwCs)—that provides independent units of protection, privilege, and execution state within a process. A process may include several lwCs, each with possibly different views of memory, file descriptors, and access capabilities. lwCs can be used to efficiently implement roll-back (process can return to a prior recorded state), isolated address spaces (lwCs within the process may have different views of memory, e.g., isolating sensitive data from network-facing components or isolating different user sessions), and privilege separation (in-process reference monitors can arbitrate and control access).

lwCs can be implemented efficiently: the overhead of a lwC is proportional to the amount of memory exclusive to the lwC; switching lwCs is quicker than switching kernel threads within the same process. We describe the lwC abstraction and API, and an implementation of lwCs within the FreeBSD 11.0 kernel. Finally, we present an evaluation of common usage patterns, including fast rollback, session isolation, sensitive data isolation, and inprocess reference monitoring, using Apache, nginx, PHP, and OpenSSL.

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@inproceedings {199327,
author = {James Litton and Anjo Vahldiek-Oberwagner and Eslam Elnikety and Deepak Garg and Bobby Bhattacharjee and Peter Druschel},
title = {Light-Weight Contexts: An {OS} Abstraction for Safety and Performance},
booktitle = {12th {USENIX} Symposium on Operating Systems Design and Implementation ({OSDI} 16)},
year = {2016},
isbn = {978-1-931971-33-1},
address = {Savannah, GA},
pages = {49--64},
url = {},
publisher = {{USENIX} Association},