CAPABILITIES AND THE ⋆-PROPERTY
10.4. BUILDING SECURE CAPABILITY SYSTEMS 147
mediation to inspect the capabilities being loaded. This mediation can be used to determine whether the capability provides write access to an object with a lower access class than the process i.e., where write permission would violate the Bell-LaPadula policy. Enforcement of such an approach requires the SCAP kernel to include labels with capabilities, labels with processes, and an MLS access policy, so that the kernel can assess whether the capability may be loaded legally. Other capability systems, the Secure Ada Target SAT [ 34 ] and the Monash capability system [ 12 ] implement similar enforcement semantics, albeit with markedly different approaches. SAT implements semantically similar checks as SCAP to ensure that any capability being loaded adheres to an MLS policy, but the enforcement is done entirely in hardware. Monash’s solution is also semantically similar, but Monash is a password capability system which limits access to write capabilities by keeping the encryption keys used for these capabilities secret. Only authorized processes can obtain the key from the system. Rather than just providing a point of mediation to decide whether to reduce capability per- missions, the EROS system defines a capability that automatically generates the correct permis- sions [ 287 ]. EROS defines the notion of a weak attribute for a capability, the combination of which we will call a weak capability. If a weak capability is used to fetch some other capabilities, all the retrieved capabilities are automatically reduced to read-only and weak capabilities. Like SCAP, the reduction is performed when the capabilities are loaded into the capability cache. Unlike SCAP, EROS enforces the ⋆-property without the need to consult an MLS policy at runtime, a potentially significant performance advantage [ 288 ]. Instead, EROS requires that an MLS policy be consulted when capabilities are created e.g., at load time to determine when a process should be given a weak capability. In order to ensure that this works, the system must ensure that any capabilities constructed that enable a process to access lower-secrecy memory must be weak capabilities. As EROS does not define how capabilities are initially distributed 1 , a higher-level service is necessary that understands the labeling of processes and capabilities, and has access to a Bell-LaPadula policy [ 23 ], so the ⋆-property is enforced correctly. The idea of a weak attribute is based on sense capabilities in KeyKOS [ 128 ] which only enable retrieval of read-only capabilities i.e., in most cases, even if the capability fetched has read-write privileges. The EROS design generalizes this by making the semantics uniform and transitive. First, weak capabilities have the same effect regardless of the type of the object referenced by the capability. Second, if a sequence of capabilities is required to retrieve some target capability, the target capability is reduced to read-only and weak if any capability in the retrieval sequence is weak.10.4.2 ENFORCING CONFINEMENT
The confinement problem was identified by Lampson in 1970 [ 177 ], so several capability system designs in the 1970s aimed to provide confinement guarantees. The HYDRA capability system [ 56 , 343 ] provided confinement by defining confined protection domains that were not allowed to store 1 EROS does check that the capabilities available to a process being to an authorized set, which also is defined external to EROS, as described below in Section 10.4.2.Parts
» SECURE OPERATING SYSTEMS 3 Operating Systerm Security
» SECURE OPERATING SYSTEMS Operating Systerm Security
» SECURITY GOALS Operating Systerm Security
» SECURITY GOALS 5 Operating Systerm Security
» TRUST MODEL Operating Systerm Security
» THREAT MODEL 7 Operating Systerm Security
» THREAT MODEL Operating Systerm Security
» SUMMARY Operating Systerm Security
» MANDATORY PROTECTION SYSTEMS PROTECTION SYSTEM 11
» PROTECTION SYSTEM 13 Operating Systerm Security
» REFERENCE MONITOR Operating Systerm Security
» REFERENCE MONITOR 15 Operating Systerm Security
» SECURE OPERATING SYSTEM DEFINITION
» SECURE OPERATING SYSTEM DEFINITION 17
» ASSESSMENT CRITERIA 19 ASSESSMENT CRITERIA
» SUMMARY 21 Operating Systerm Security
» MULTICS HISTORY THE MULTICS SYSTEM
» MULTICS FUNDAMENTALS THE MULTICS SYSTEM 25
» MULTICS SECURITY FUNDAMENTALS THE MULTICS SYSTEM 25
» MULTICS PROTECTION SYSTEM MODELS
» MULTICS PROTECTION SYSTEM THE MULTICS SYSTEM 29
» MULTICS REFERENCE MONITOR THE MULTICS SYSTEM 31
» MULTICS SECURITY 33 Operating Systerm Security
» MULTICS SECURITY Operating Systerm Security
» MULTICS SECURITY 35 Operating Systerm Security
» MULTICS VULNERABILITY ANALYSIS Operating Systerm Security
» SUMMARY 37 Operating Systerm Security
» UNIX HISTORY SYSTEM HISTORIES
» WINDOWS HISTORY SYSTEM HISTORIES
» UNIX SECURITY 41 Operating Systerm Security
» UNIX PROTECTION SYSTEM UNIX SECURITY
» UNIX AUTHORIZATION UNIX SECURITY 43
» Complete Mediation: How does the reference monitor interface ensure that all security-
» Complete Mediation: Does the reference monitor interface mediate security-sensitive oper-
» Complete Mediation: How do we verify that the reference monitor interface provides com-
» Tamperproof: How does the system protect the reference monitor, including its protection
» Tamperproof: Does the system’s protection system protect the trusted computing base pro-
» UNIX VULNERABILITIES UNIX SECURITY 47
» WINDOWS SECURITY 49 Operating Systerm Security
» WINDOWS PROTECTION SYSTEM WINDOWS SECURITY
» WINDOWS AUTHORIZATION WINDOWS SECURITY 51
» Verifiable: What is basis for the correctness of the system’s trusted computing base?
» WINDOWS VULNERABILITIES WINDOWS SECURITY 55
» INFORMATION FLOW Operating Systerm Security
» INFORMATION FLOW SECRECY MODELS 59
» INFORMATION FLOW SECRECY MODELS
» BELL-LAPADULA MODEL INFORMATION FLOW SECRECY MODELS 61
» INFORMATION FLOW SECRECY MODELS 63
» INFORMATION FLOW INTEGRITY MODELS
» BIBA INTEGRITY MODEL INFORMATION FLOW INTEGRITY MODELS 65
» LOW-WATER MARK INTEGRITY INFORMATION FLOW INTEGRITY MODELS 67
» CLARK-WILSON INTEGRITY INFORMATION FLOW INTEGRITY MODELS 67
» THE CHALLENGE OF TRUSTED PROCESSES
» COVERT CHANNELS Operating Systerm Security
» CHANNEL TYPES COVERT CHANNELS 71
» SUMMARY 73 Operating Systerm Security
» THE SECURITY KERNEL Operating Systerm Security
» SECURE COMMUNICATIONS PROCESSOR 77 Operating Systerm Security
» SCOMP ARCHITECTURE SECURE COMMUNICATIONS PROCESSOR
» SCOMP HARDWARE SECURE COMMUNICATIONS PROCESSOR 79
» SCOMP TRUSTED OPERATING PROGRAM
» SCOMP KERNEL INTERFACE PACKAGE
» SECURE COMMUNICATIONS PROCESSOR 85 Operating Systerm Security
» GEMINI SECURE OPERATING SYSTEM
» GEMINI SECURE OPERATING SYSTEM 87
» SUMMARY 89 Operating Systerm Security
» RETROFITTING SECURITY INTO A COMMERCIAL OS
» HISTORY OF RETROFITTING COMMERCIAL OS’S 93
» HISTORY OF RETROFITTING COMMERCIAL OS’S COMMERCIAL ERA
» MICROKERNEL ERA 95 Operating Systerm Security
» MICROKERNEL ERA Operating Systerm Security
» UNIX ERA 97 Operating Systerm Security
» RECENT UNIX SYSTEMS UNIX ERA 99
» SUMMARY 101 Operating Systerm Security
» TRUSTED EXTENSIONS ACCESS CONTROL
» SOLARIS COMPATIBILITY 105 Operating Systerm Security
» SOLARIS COMPATIBILITY Operating Systerm Security
» TRUSTED EXTENSIONS MEDIATION Operating Systerm Security
» TRUSTED EXTENSIONS MEDIATION 107 Operating Systerm Security
» PROCESS RIGHTS MANAGEMENT PRIVILEGES
» PRIVILEGE BRACKETING AND RELINQUISHING
» CONTROLLING PRIVILEGE ESCALATION PROCESS RIGHTS MANAGEMENT PRIVILEGES 111
» ASSIGNED PRIVILEGES AND SAFEGUARDS
» RBAC AUTHORIZATIONS ROLE-BASED ACCESS CONTROL RBAC
» CONVERTING THE SUPERUSER TO A ROLE
» TRUSTED EXTENSIONS NETWORKING 115 Operating Systerm Security
» TRUSTED EXTENSIONS NETWORKING Operating Systerm Security
» TRUSTED EXTENSIONS MULTILEVEL SERVICES TRUSTED EXTENSIONS MULTILEVEL SERVICES 117
» TRUSTED EXTENSIONS ADMINISTRATION Operating Systerm Security
» SUMMARY 119 Operating Systerm Security
» LSM HISTORY LINUX SECURITY MODULES
» LSM IMPLEMENTATION LINUX SECURITY MODULES 123
» LINUX SECURITY MODULES 125 Operating Systerm Security
» SELINUX REFERENCE MONITOR SECURITY-ENHANCED LINUX
» SECURITY-ENHANCED LINUX 127 Operating Systerm Security
» SELINUX PROTECTION STATE SECURITY-ENHANCED LINUX 129
» SELINUX LABELING STATE SECURITY-ENHANCED LINUX 131
» SELINUX TRANSITION STATE SECURITY-ENHANCED LINUX 133
» SELINUX TRUSTED PROGRAMS SECURITY-ENHANCED LINUX 135
» SUMMARY 139 Operating Systerm Security
» CAPABILITY SYSTEM FUNDAMENTALS Operating Systerm Security
» CAPABILITY SECURITY Operating Systerm Security
» CHALLENGES IN SECURE CAPABILITY SYSTEMS 143
» CAPABILITIES AND THE ⋆-PROPERTY
» CAPABILITIES AND CONFINEMENT CHALLENGES IN SECURE CAPABILITY SYSTEMS
» CAPABILITIES AND POLICY CHANGES
» ENFORCING THE ⋆-PROPERTY BUILDING SECURE CAPABILITY SYSTEMS
» ENFORCING CONFINEMENT BUILDING SECURE CAPABILITY SYSTEMS 147
» REVOKING CAPABILITIES BUILDING SECURE CAPABILITY SYSTEMS 149
» SUMMARY 151 SUMMARY Operating Systerm Security
» SEPARATION KERNELS 155 SEPARATION KERNELS
» VAX VMM DESIGN VAX VMM SECURITY KERNEL
» SECURITY IN OTHER VIRTUAL MACHINE SYSTEMS 163
» SECURITY IN OTHER VIRTUAL MACHINE SYSTEMS
» SECURITY IN OTHER VIRTUAL MACHINE SYSTEMS 165
» SUMMARY 167 Operating Systerm Security
» ORANGE BOOK Operating Systerm Security
» ORANGE BOOK 171 Operating Systerm Security
» COMMON CRITERIA CONCEPTS COMMON CRITERIA
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