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Capability machines are a special form of CPUs that offer fine-grained privilege separation using a form of authority-carrying values known as capabilities. The CHERI capability machine offers local capabilities, which could be used as a cheap but restricted form of capability revocation. Unfortunately, local capability revocation is unrealistic in practice because large amounts of stack memory need to be cleared as a security precaution. In this paper, we address this shortcoming by introducing uninitialized capabilities: a new form of capabilities that represent read/write authority to a block of memory without exposing the memory's initial contents. We provide a mechanically verified program logic for reasoning about programs on a capability machine with the new feature and we formalize and prove capability safety in the form of a universal contract for untrusted code. We use uninitialized capabilities for making a previously-proposed secure calling convention efficient and prove its security using the program logic. Finally, we report on a proof-of-concept implementation of uninitialized capabilities on the CHERI capability machine.
|Number of pages||30|
|Journal||Proceedings of the ACM on Programming Languages|
|Publication status||Published - 4 Jan 2021|
|Event||ACM SIGPLAN Symposium on Principles of Programming Languages - Copenhagen, Denmark|
Duration: 17 Jan 2021 → 22 Jan 2021
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1/09/19 → 31/12/22
1/02/19 → 31/01/23