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Information flow type systems enforce the security property of noninterference by detecting unauthorized data flows at compile-time. However, they require precise type annotations, making them difficult to use in practice as much of the legacy infrastructure is written in untyped or dynamically-typed languages. Gradual typing seamlessly integrates static and dynamic typing, providing the best of both approaches, and has been applied to information flow control, where information flow monitors are derived from gradual security types. Prior work on gradual information flow typing uncovered tensions between noninterference and the dynamic gradual guarantee- the property that less precise security type annotations in a program should not cause more runtime errors.This paper re-examines the connection between gradual information flow types and information flow monitors to identify the root cause of the tension between the gradual guarantees and noninterference. We develop runtime semantics for a simple imperative language with gradual information flow types that provides both noninterference and gradual guarantees. We leverage a proof technique developed for FlowML and reduce noninterference proofs to preservation proofs.
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Reconciling noninterference and gradual typing
One of the standard correctness criteria for gradual typing is the dynamic gradual guarantee, which ensures that loosening type annotations in a program does not affect its behavior in arbitrary ways. Though natural, prior work has pointed out that the guarantee does not hold of any gradual type system for information-flow control. Toro et al.'s GSLRef language, for example, had to abandon it to validate noninterference. We show that we can solve this conflict by avoiding a feature of prior proposals: type-guided classification, or the use of type ascription to classify data. Gradual languages require run-time secrecy labels to enforce security dynamically; if type ascription merely checks these labels without modifying them (that is, without classifying data), it cannot violate the dynamic gradual guarantee. We demonstrate this idea with GLIO, a gradual type system based on the LIO library that enforces both the gradual guarantee and noninterference, featuring higher-order functions, general references, coarsegrained information-flow control, security subtyping and first-class labels. We give the language a domain-theoretic semantics, using Pitts' framework of relational structures to prove noninterference and the dynamic gradual guarantee.
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- Award ID(s):
- 1704542
- PAR ID:
- 10184238
- Date Published:
- Journal Name:
- Proceedings of the 35th Annual ACM/IEEE Symposium on Logic in Computer Science
- Page Range / eLocation ID:
- 116 to 129
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Fine-grained information flow control (IFC) ensures confidentiality and integrity at the programming language level by ensuring that high-secrecy values do not affect low-secrecy values and that low-integrity values do not affect high-integrity values. However, prior support for fine-grained IFC is impractical: It either analyzes programs using whole-program static analysis, detecting false IFC violations; or it extends the language and compiler, thwarting adoption. Recent work called Cocoon demonstrates how to provide fine-grained IFC for Rust programs without modifying the language or compiler, but it is limited to static secrecy labels, and its case studies are limited. This paper introduces an approach called Carapace that employs Cocoon’s core approach and supports both static and dynamic IFC and supports both secrecy and integrity. We demonstrate Carapace using three case studies involving real applications and comprehensive security policies. An evaluation shows that applications can be retrofitted to use Carapace with relatively few changes, while incurring negligible run-time overhead in most cases. Carapace advances the state of the art by being the first hybrid static–dynamic IFC that works with an off-the-shelf language—Rust—and its unmodified compilermore » « less
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.1145/3373718.3394778
