Details of Grant 

EPSRC Reference:	EP/X015963/1
Title:	Chrompartments: Hybrid Compartmentalisation for Web Browsers
Principal Investigator:	Tratt, Professor L
Other Investigators:	Jones, Professor TM
Researcher Co-Investigators:	Dr AT Markettos
Project Partners:	ARM Ltd
Department:	Informatics
Organisation:	Kings College London
Scheme:	Standard Research
Starts:	06 July 2022	Ends:	05 January 2025	Value (£):	1,077,295
EPSRC Research Topic Classifications:	Computer Sys. & Architecture Software Engineering
EPSRC Industrial Sector Classifications:	Information Technologies
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Summary on Grant Application Form
The Chrompartments project will explore hybrid compartmentalisation for web browsers using Chrome as a concrete example. Browsers are systemically important but present a large attack surface due to their scale and complexity: they are a magnet for attackers with frequent published attacks. Chrompartments will use CHERI to split browsers into mutually distrusting compartments, making them more resilient and performant. We will use Chrome (in the form of its open-source variant Chromium) as the vehicle for our experimentation because it is the most widely used browser and it is already partially compartmentalised in a way that we can build upon. Chrome tries when possible to split itself into process-based compartments (roughly speaking: 1 process per tab; and some core components such as graphics are split into separate processes). However, this model is heavyweight: OS processes consume considerable resources and many devices (particularly phones) quickly hit their process limits, forcing the browser to merge multiple tabs in a single process; and communication between processes is painfully slow. Some security-critical components (e.g. V8, Chrome's JavaScript engine) would ideally be split out too, but resource and performance constraints make this impractical. We will use CHERI's "hybrid mode" (i.e. where both traditional width pointers can be used alongside capabilities) to split Chrome into process-like compartments. Most code will use traditional width pointers and will be boxed into compartments; pure capabilities will allow us to emulate various forms of inter-compartment communication. We hypothesise that this will lead to greater practical security, and require fewer changes, than the ideal pure-capability-based compartmentalisation. Our overall aim is thus first to replace Chrome's process-based model with CHERI compartments, and then break those crude compartments into finer-grained compartments, enhancing security without significantly affecting performance. As well as significant engineering, there is also important research: processes give some guarantees (e.g. against some side-channel attacks) that CHERI compartments do not currently give. We will explore these guarantees and replicate them for CHERI compartments where their existence is necessary for browser security. After converting process-based isolation to CHERI compartmentalisation, Chrompartments will operate in two strands: V8, the JavaScript engine; and the graphics stack. Both strands contain significant challenges: for example, the graphics stack is currently contained within a single process no matter how many sites are using it. Understanding the right compartmentalisation points will be critical to Chrompartments' success and lead to a much greater understanding of how to use CHERI on large-scale systems.
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