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School of Computer Science & Engineering
University of New South Wales
 Advanced Operating Systems 
 COMP9242 2002/S2 

Hot Topics -- Cool Systems

Cool System: EROS[SSF99]

Idea: fast, secure, reliable OS

Features:

• segregated capabilities,
• single-level store,
• persistence (via checkpointing),
• fast,
• mandatory access control,
• formal proof of confinement[SW00].

EROS is a re-design of KeyKOS[BFF$^+$92].

EROS memory and access management

Clists form page table

EROS access rights management

• Limit propagation and support revocation of rights by:
  • ``weak capabilities'':
    • reading/writing any cap via a weak cap makes it R/O and weak
    • can obtain transitive read-only access
  • indirection:
    • Reference monitor (similar to L4 chief mediates cap transfer
    • inserts forwarding objects to capabilities
    • implements security policy
    • on change of policy can revoke caps by revoking forwarding object

EROS performance

Note: No data on cost of indirection for MAC.

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