BIB-VERSION:: CS-TR-v2.0
ID:: ncstrl.dartmouthcs//TR96-287
ENTRY:: June 01, 1996
ORGANIZATION:: Dartmouth College, Computer Science
TITLE:: Implementation and Analysis of Software Based Fault Isolation
TYPE:: Technical Report (paper)
REVISION:: 1
AUTHOR:: Silver, Scott M.
DATE:: June 1996	
RETRIEVAL:: For a paper copy, email <reports@cs.dartmouth.edu>
RETRIEVAL:: For a paper copy, write to
       Technical Report Librarian
       Department of Computer Science
       Dartmouth College
       6211 Sudikoff Laboratory
       Hanover, NH 03755-3510
       USA
RETRIEVAL:: Compressed Postscript at http://www.cs.dartmouth.edu/reports/TR96-287.ps.Z
RETRIEVAL:: PDF at http://www.cs.dartmouth.edu/reports/TR96-287.pdf
ABSTRACT:: 
   Extensible applications rely upon user-supplied, untrusted modules
to extend their functionality.  To remain reliable, applications must
isolate themselves from user modules.  One method places each user
module in a separate address space (process), which uses hardware
virtual memory support to isolate the user process.  Costly
inter-process communication, however, prohibits frequent communication
between the application and the untrusted module.  We implemented and
analyzed a software method for isolating an application from user
modules.  The technique uses a single address space.  We provide a
logical address space and per-module access to system resources for
each module.  Our software technique is a two-step process.  First, we
augment a module's code so that it cannot access any address outside
of an assigned range.  Second, we prevent the module from using system
calls to access resources outside of its fault domain.
   This method for software isolation has two particular advantages
over processes.  First, for frequently communicating modules, we
significantly reduce context switch time.  Thus, we demonstrate
near-optimal inter-module communication using software fault
isolation. Second, our software-based techniques provide an efficient
and expedient solution in situations where only one address space is
available (e.g., kernel, or a single-address-space operating system).
NOTE:: 
A Senior Undergraduate Honors Thesis in Computer Science.
END:: ncstrl.dartmouthcs//TR96-287