CHERIoT-Platform/cheriot-rtos

Create sub-quotas for allocation capabilities

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#140 opened on Nov 29, 2023

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good first issue

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Description

The allocator currently deals with static heap quotas. Sometimes it's useful to allow another compartment to allocate memory on your behalf, but not to consume your entire quota. We should allow a mechanism for creating a new quota object that contains part of an existing quota. This should have the same ID as the original, so that objects can be freed in both.

The main complication in this is that, currently, quotas are checked without the allocator lock being held (I think). We need to make sure that the mechanism is robust in the presence of a quota being deallocated during an allocation or deallocation operation.

Contributor guide

Research direction
Investigate the current quota checking mechanism, particularly whether the allocator lock is held during quota checks. Understand how quotas are checked without the lock and the implications for concurrency. Propose a design for sub quotas that safely handles concurrent deallocation of quotas.
Tech stack
None
Domain
infrastructuresecurity
Issue type
Feature
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
3
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-2 days
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
Active
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
Needs investigation
Prerequisites
C++Concurrency
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
20