Patent Publication Number: US-4545012-A

Title: Access control system for use in a digital computer system with object-based addressing and call and return operations

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present patent application is related to U.S. patent application Ser. No. 266,407, System for Controlling Access to Data in a Digital Processing System (as amended), Ser. No. 266,409, Digital Data Processing System, and Ser. No. 266,530, Universal Addressing System for a Digital Data Processing System (as amended), all filed on even date with the present application and assigned to the assignee of the present application. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to digital data processing systems and more particularly to systems for controlling access to data in digital data processing systems. 
     2. Description of Prior Art 
     A general trend in the development of data processing systems has been towards systems suitable for use in interconnected data processing networks. Another trend has been towards data processing systems wherein the internal structure of the system is flexible, protected from users, and effectively invisible to the user and wherein the user is presented with a flexible and simplified interface to the system. 
     Certain problems and shortcomings affecting the realization of such a data processing system have appeared repeatedly in the prior art and must be overcome to create a data processing system having the above attributes. These prior art problems and limitations include the following topics. 
     First, the data processing systems of the prior art have not provided a system wide addressing system suitable for use in common by a large number of data processing systems interconnected into a network. Addressing systems of the prior art have not provided sufficiently large address spaces and have not allowed information to be permanently and uniquely identified. Prior addressing systems have not made provisions for information to be located and identified as to type or format, and have not provided sufficient granularity. In addition, prior addressing systems have reflected the physical structure of particular data processing systems. That is, the addressing systems have been dependent upon whether a particular computer was, for example, an 8, 16, 32, 64 or 128 bit machine. Since prior data processing systems have incorporated addressing mechanisms wherein the actual physical structure of the processing system is apparent to the user, the operations a user could perform have been limited by the addressing mechanisms. In addition, prior processor systems have operated as fixed word length machines, further limiting user operations. 
     Prior data processing systems have not provided effective protection mechanisms preventing one user from effecting another user&#39;s data and programs without permission. Such protection mechanisms have not allowed unique, positive identification of users requesting access to information, or of information, nor have such mechanisms been sufficiently flexible in operation. In addition, access rights have pertained to the users rather than to the information, so that control of access rights has been difficult. Finally, prior art protection mechanisms have allowed the use of &#34;Trojan Horse arguments&#34;. That is, users not having access rights to certain information have been able to gain access to that information through another user or procedure having such access rights. 
     Yet another problem of the prior art is that of providing a simple and flexible interface user interface to a data processing system. The character of user&#39;s interface to a data processing system is determined, in part, by the means by which a user refers to and identifies operands and procedures of the user&#39;s programs and by the instruction structure of the system. Operands and procedures are customarily referred to and identified by some form of logical address having points of reference, and validity, only within a user&#39;s program. These addresses must be translated into logical and physical addresses within a data processing system each time a program is executed, and must then be frequently retranslated or generated during execution of a program. In addition, a user must provide specific instructions as to data format and handling. As such reference to operands or procedures typically comprise a major portion of the instruction stream of the user&#39;s program and requires numerous machine translations and operations to implement. A user&#39;s interface to a conventional system is thereby complicated, and the speed of execution of programs reduced, because of the complexity of the program references to operands and procedures. 
     A data processing system&#39;s instruction structure includes both the instructions for controlling system operations and the means by which these instructions are executed. Conventional data processing systems are designed to efficiently execute instructions in one or two user languages, for example, FORTRAN or COBOL. Programs written in any other language are not efficiently executable. In addition, a user is often faced with difficult programming problems when using any high level language other than the particular one or two languages that a particular conventional system is designed to utilize. 
     Yet another problem in conventional data processing systems is that of protecting the system&#39;s internal mechanisms, for example, stack mechanisms and internal control mechanisms, from accidental or malicious interference by a user. 
     Finally, the internal structure and operation of prior art data processing systems have not been flexible, or adaptive, in structure and operation. That is, the internal structure structure and operation of prior systems have not allowed the systems to be easily modified or adapted to meet particular data processing requirements. Such modifications may include changes in internal memory capacity, such as the addition or deletion of special purpose subsystems, for example, floating point or array processors. In addition, such modifications have significantly effected the users interface with the system. Ideally, the actual physical structure and operation of the data processing system should not be apparent at the user interface. 
     The present invention provides data processing system improvements and features which solve the above-described problems and limitations. 
     SUMMARY OF THE INVENTION 
     The present invention relates generally to digital computer systems and more specifically to access control systems employed in digital computer systems which commence executions of procedures by means of call operations and terminate executions by means of return operations. In the access control system of the present invention, the digital computer system&#39;s memory is organized into objects. Data items stored in the memory are locatable by means of the objects. Each procedure executed in the digital computer system may access only a limited set of objects. Those objects accessible to a given procedure are termed a domain. 
     The access control system responds to each memory operation specifier by performing the specified memory operation on the specified data item only if the object by which the data item is locatable is in the domain accessible to the procedure currently being executed. The access control system includes a secure stack object upon which only the access control system performs memory operations. When a call operation commences execution of a procedure which has a different domain from that of the procedure currently being executed, a component of the access control system saves information required to return to the domain of the procedure currently being executed on the secure stack object. When a return operation terminates execution of a procedure which has a domain different from that of the procedure whose execution is resumed by the return statement, another component of the access control system obtains the information required to return to the domain of the procedure whose execution is being resumed from the secure stack object. 
     Other aspects of the invention include the use of access control list entries including subject templates to limit access to objects to certain subjects representing entities for which the digital computer system executes instructions and the formation of subjects out of a plurality of object identifiers specifying objects containing information about the subject. 
     It is thus an object of the invention to provide an improved digital computer system. 
     It is an additional object of the invention to provide an improved access control system for a digital computer system. 
     It is a further object of the invention to provide an access control system including domains of objects accessible only to certain procedures and secure stack objects for saving information used to return to a domain. 
     It is another object of the invention to provide an access control system utilizing access control list entries containing subject templates to control access to objects; and 
     It is a still further object of the invention to provide an access control system utilizing a subject consisting of a plurality of object identifiers specifying objects containing information about the subject. 
    
    
     Other objects, advantages and features of the present invention will be understood by those of ordinary skill in the art, after referring to the following detailed description of the preferred embodiments and drawings wherein: 
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a partial block diagram of a computer system incorporating the present invention. 
    
    
     This application incorporates by reference the entire application, Ser. No. 266,402, filed on May 22, 1981, of Baxter et al., now issued as U.S. Pat. No. 4,455,602, on June 19, 1984. 
     More particularly, attention is directed to FIGS. 103, 270, 271, 301, 408-440, 447, 463, 467, 469, 470 and 471 of the drawings in application Ser. No. 266,402, and to that part of the descriptive portion of the specification, particularly at pages 777-780, 813-841 and 1016-1057 thereof, which relate to the subject matter of the claims herein.