Abstract:
The Java Virtual Machine (JVM) can be decoupled from its Java-enabled browser. To maintain access to certain system resources (a “privilege”) by applets, each Java thread that enables the privilege will now create an entry that describes the privilege in a linked list based on the stack frame address. Sufficient information is stored in the link list for validation purposes. Further, system classes that require specific privileges will have them implicitly granted by an implicit privilege list.

Description:
BACKGROUND OF THE INVENTION 
   1. Technical Field 
   The present invention relates to a system for decoupling a java virtual machine (JVM) from a browser. Specifically, the invention relates to a system to retain applet security privileges outside of the JVM, thereby allowing internet browser decoupling from the JVM. 
   2. Description of Related Art 
   The Internet, also referred to as an “internetwork”, in communications is a set of computer networks, possibly dissimilar, joined together by means of gateways that handle data transfer and the conversion of messages from the sending network to the protocols used by the receiving network (with packets if necessary). When capitalized, the term “Internet” refers to the collection of networks and gateways that use the TCP/IP suite of protocols. 
   The Internet has become a cultural fixture as a source of both information and entertainment. Many businesses are creating Internet sites as an integral part of their marketing efforts, informing consumers of the products or services offered by the business or providing other information seeking to engender brand loyalty. Many federal, state, and local government agencies are also employing Internet sites for informational purposes, particularly agencies which must interact with virtually all segments of society such as the Internal Revenue Service and secretaries of state. Operating costs may be reduced by providing informational guides and/or searchable databases of public records online. 
   Currently, the most commonly employed method of transferring data over the Internet is to employ the World Wide Web environment, also called simply “the web”. Other Internet resources exist for transferring information, such as File Transfer Protocol (FTP) and Gopher, but have not achieved the popularity of the web. In the web environment, servers and clients effect data transaction using the Hypertext Transfer Protocol (HTTP), a known protocol for handling the transfer of various data files (e.g., text, still graphic images, audio, motion video, etc.). Information is formatted for presentation to a user by a standard page description language, the Hypertext Markup Language (HTML). In addition to basic presentation formatting, HTML allows developers to specify “links” to other web resources identified by a Uniform Resource Locator (URL). A URL is a special syntax identifier defining a communications path to specific information. Each logical block of information accessible to a client, called a “page” or a “web page”, is identified by a URL. The URL provides a universal, consistent method for finding and accessing this information by the web “browser”. A browser is a program capable of submitting a request for information identified by a URL at the client machine. Retrieval of information on the web is generally accomplished with an HTML-compatible browser. 
   When a user desires to retrieve a page, a request is submitted to a server connected to a client computer at which the user is located and may be handled by a series of servers to effect retrieval of the requested information. The information is provided to the client formatted according to HTML. Typically, personal computers (PCs) along with work stations are typically used to access the Internet. 
   Often applications or programs may be sent to a computer from a web server across the Internet. Java applications are becoming increasingly more prevalent as the type of application sent between web servers and client computers. Java applications are common on the Internet and becoming more increasingly common in intranets and in other types of networks used in businesses. 
   Java is an object oriented programming language and environment focusing on defining data as objects and the methods that may be applied to those objects. Java supports only a single inheritance, meaning that each class can inherit from only one other class at any given time. Java also allows for the creation of totally abstract classes known as interfaces, which allow the defining of methods that may be shared with several classes without regard for how other classes are handling the methods. 
   The Java virtual machine (JVM) is a virtual computer component that resides only in memory. The JVM allows Java programs to be executed on a different platform as opposed to only the one platform for which the code was compiled. Java programs are compiled for the JVM. In this manner, Java is able to support applications for many types of data processing systems, which may contain a variety of central processing units and operating systems architectures. To enable a Java application to execute on different types of data processing systems, a compiler typically generates an architecture-neutral file format—the compiled code is executable on many processors, given the presence of the Java run-time system. The Java compiler generates bytecode instructions that are non-specific to a particular computer architecture. A bytecode is a machine independent code generated by the Java compiler and executed by a Java interpreter. A Java interpreter is a part in the JVM that alternately decodes and interprets a bytecode or bytecodes. These bytecode instructions are designed to be easy to interpret on any computer and easily translated on the fly into native machine code. 
   Many currently available web browsers, such as Netscape Communicator, which is available from Netscape Communications Corporation, incorporate fixed, embedded JVMs in which the browsers pass fixed options to the JVM. Presently, however, JVMs updates are provided more often than web browser updates. Such a situation prevents users from taking advantage of improved versions of JVMs until the web browser is updated. Therefore, it would be advantageous to have an improved method and apparatus for providing users an ability to use more recent versions of JVMs without having to wait for an updated version of the web browser. Specifically, a fixed JVM within the browser limits the flexibility of developers and users of Java applets within the browser. “Applets” are mini applications that typically run inside a Java-enabled browser. 
   Netscape implements a proprietary Java security scheme within their browser (and JVM). Applets can request, and subsequently be granted certain privileges, such as being able to read or write to the local hard drive. These privileges, when granted, are stored in the JVM&#39;s call stack frame which corresponds to the method which has been granted access. These privileges remain in effect until the method (function) which requested it goes out of scope. In other words, when the function is popped from the call stack. These privileges are also removed when a user explicitly reverts the privilege. 
   The implementation of storing privileges on the JVM&#39;s stack frame requires JVM modifications for its implementation, since the stack frame data structure is internal to the JVM. This implementation prevents the usage of a de-integrated JVM. Netscape has also changed many system Java classes to explicitly code enable Privilege/revert Privilege calls. By doing so, a copy of a Java source file for a given level of Java is modified with these calls to enable or revert privileges. This locks the browser into a particular level of Java source. 
   Therefore, a need exists for a method of decoupling the JVM from the browser. Once decoupled, a more up-to-date version of the JVM can be utilized. However, applet security privileges must be retained outside of the JVM by such a system. 
   SUMMARY OF THE INVENTION 
   The present invention addresses the need to decouple the JVM from the browser while retaining applet security privileges. Each Java thread that enables a privilege will now create an entry that describes the privilege in a linked list based on the stack frame address. Sufficient information is stored in the link list entry for validation purposes, to guard against the case where a function that was granted privilege has since returned and the same stack frame is being reused by another function which should not have privilege. The information that is kept is the method name and signature (parameter list) of the function requesting the privilege, as well as the calling function&#39;s return address (instruction pointer). When a query is done to determine if the applet has the required privilege, the linked list for its thread will be searched and the privilege (if found and valid) will be returned. Privileges are reverted by removing the element from the linked list. 
   System Java classes also no longer need to be modified with enable/revert privilege calls. Instead, system classes that require specific privileges will have them implicitly granted. An implicit privilege list is created in memory. The implicit privilege list can map system classes, functions within them that require privileges, and the privileges that are needed. When a request is made to determine if a function has the required privilege, the linked list of privileges will first be checked. If no privilege is found, a subsequent search of the implicit privilege list will determine whether the requesting function is allowed access to the resource. This apparatus can also be used in future implementations for storing additional Java stack frame-based information. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The novel features believed characteristic of the invention are set forth in the appended claims. The invention itself, however, as well as a preferred mode of use, further objectives and advantages thereof, will best be understood by reference to the following detailed description of an illustrative embodiment when read in conjunction with the accompanying drawings, wherein: 
       FIG. 1  is a pictorial representation of a distributed data processing system in which the present invention may be implemented; 
       FIG. 2  is a block diagram of a data processing system that may be implemented as a server; 
       FIG. 3  is a block diagram of a data processing system in which the present invention may be implemented; 
       FIG. 4  is a block diagram illustrating the stack frame shadow apparatus used in the implementation of the present invention; 
       FIG. 5  is a block diagram illustrating the Java stack frame data structure and the Java stack frame extension data structure; 
       FIG. 6  is a flow chart of the method of setting a Java stack frame extension in the apparatus of  FIG. 4 ; 
       FIG. 7  is a flow chart of the method of querying to get a Java stack frame extension in the apparatus; and 
       FIG. 8  is a flow chart of the method for removing a Java stack frame extension in the apparatus. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   With reference now to the figures, and in particular with reference to  FIG. 1 , a pictorial representation of a distributed data processing system in which the present invention may be implemented is depicted. 
   Distributed data processing system  100  is a network of computers in which the present invention may be implemented. Distributed data processing system  100  contains a network  102 , which is the medium used to provide communications links between various devices and computers connected together within distributed data processing system  100 . Network  102  may include permanent connections, such as wire or fiber optic cables, or temporary connections made through telephone connections. 
   In the depicted example, a server  104  is connected to network  102  along with storage unit  106 . In addition, clients  108 ,  110 , and  112  also are connected to a network  102 . These clients  108 ,  110 , and  112  may be, for example, personal computers of network computers. For purposes of this application, a network computer is any computer, coupled to a network, which receives a program or other application from another computer coupled to the network. In the depicted example, server  104  provides data, such as boot files, operating system images, and applications to NCs  108 - 112 . NCs - 108 ,  110 , and  112  are clients to server  104 . Distributed data processing system  100  may include additional servers, clients, and other devices not shown. In the depicted example, distributed data processing system  100  is the Internet with network  102  representing a worldwide collection of networks and gateways that use the TCP/IP suite of protocols to communicate with one another. At the heart of the Internet is a backbone of high-speed data communication lines between major nodes or host computers, consisting of thousands of commercial, government, educational, and other computer systems, that route data and messages. Of course, distributed data processing system  100  also may be implemented as an umber of different types of networks, such as for example, an intranet or a local area network. 
     FIG. 1  is intended as an example, and not as an architectural limitation for the processes of the present invention. 
   Referring to  FIG. 2 , a block diagram of a data processing system which may be implemented as a server, such as server  104  in  FIG. 1 , is depicted in accordance to the present invention. Data processing system  200  may be a symmetric multiprocessor (SMP) system including a plurality of processors  202  and  204  connected to system bus  206 . Alternatively, a single processor system may be employed. Also connected to system bus  206  is memory controller/cache  208 , which provides an interface to local memory  209 . I/O bus bridge  210  is connected to system bus  206  and provides an interface to I/O bus  212 . Memory controller/cache  208  and I/O bus bridge  210  may be integrated as depicted. 
   Peripheral component interconnect (PCI) bus bridge  214  connected to I/O bus  212  provides an interface to PCI local bus  216 . A number of modems  218 - 220  may be connected to PCI bus  216 . Typical PCI bus implementations will support four PCI expansion slots or add-in connectors. Communications links to network computers  108 - 112  in  FIG. 1  may be provided through modem  218  and network adapter  220  connected to PCI local bus  216  through add-in boards. 
   Additional PCI bus bridges  222  and  224  provide interfaces for additional PCI buses  226  and  228 , from which additional modems or network adapters may be supported. In this manner, server  200  allows connections to multiple network computers. A memory mapped graphics adapter  230  and hard disk  232  may also be connected to I/O bus  212  as depicted, either directly or indirectly. 
   Those of ordinary skill in the art will appreciate that the hardware depicted in  FIG. 2  may vary. For example, other peripheral devices, such as optical disk drive and the like also may be used in addition or in place of the hardware depicted. The depicted example is not meant to imply architectural limitations with respect to the present invention. 
   The data processing system depicted in  FIG. 2  may be, for example, an IBM RISC/System  6000  system, a product of International Business Machines Corporation in Armonk, N Y., running the Advanced Interactive Executive (AIX) operating system. 
   With reference now to  FIG. 3 , a block diagram of a data processing system  300  in which the present invention may be implemented is illustrated. Data processing system  300  is an example of a client computer. Data processing system  300  employs a peripheral component interconnect (PCI) local bus architecture. Although the depicted example employs a PCI bus, other bus architectures such as Micro Channel and ISA may be used. Processor  302  and main memory  304  are connected to PCI local bus  306  through PCI bridge  308 . PCI bridge  308  also may include an integrated memory controller and cache memory for processor  302 . Additional connections to PCI local bus  306  may be made through direct component interconnection or through add-in boards. In the depicted example, local area network (LAN) adapter  310 , SCSI host bus adapter  312 , and expansion bus interface  314  are connected to PCI local bus  306  by direct component connection. In contrast, audio adapter  316 , graphics adapter  318 , and audio/video adapter (A/V)  319  are connected to PCI local bus  306  by add-in boards inserted into expansion slots. Expansion bus interface  314  provides a connection for a keyboard and mouse adapter  320 , modem  322 , and additional memory  324 . SCSI host bus adapter  112  provides a connection for hard disk drive  326 , tape drive  328 , and CD-ROM  330  in the depicted example. Typical PCI local bus implementations will support three or four PCI expansion slots or add-in connectors. 
   An operating system runs on processor  302  and is used to coordinate and provide control of various components within data processing system  300  in FIG.  1 . The operating system may be a commercially available operating system such as OS/2, which is available from International Business Machines Corporation. “OS/2” is a trademark of from International Business Machines Corporation. An object oriented programming system such as Java may run in conjunction with the operating system and provides calls to the operating system from Java programs or applications executing on data processing system  300 . Instructions for the operating system, the object-oriented operating system, and applications or programs are located on storage devices, such as hard disk drive  326  and may be loaded into main memory  304  for execution by processor  302 . 
   Those of ordinary skill in the art will appreciate that the hardware in  FIG. 3  may vary depending on the implementation. For example, other peripheral devices, such as optical disk drives and the like may be used in addition to or in place of the hardware depicted in FIG.  3 . The depicted example is not meant to imply architectural limitations with respect to the present invention. For example, the processes of the present invention may be applied to multiprocessor data processing system. 
     FIG. 4  is a block diagram illustrating the relationship between the JVM and the browser and also illustrating the basic steps for creating the linked list. The system  400  includes a browser  402 . The browser can incorporate or interact with an existing JVM  404 . The existing JVM includes a stack frame for a first thread  406  and a stack frame for a second thread  408 . As mentioned above, privileges are stored in the stack frames. Each stack can contain a plurality of frames such as those designated by the x and y arrows. Under normal operation, the internet browser  402  queries the existing JVM  404  to get a stack frame (step  410 ). In response, the existing JVM returns the appropriate stack frame (step  412 ). The present invention involves the creation of a stack frame shadow apparatus  426 . The creation of the stack frame shadow apparatus involves setting the stack frame extension using the thread identifier and frame (step  414 ). Then, when the browser needs to know if a privilege is available, the stack frame shadow apparatus  426  is queried to get the frame extension by thread identifier and frame (step  416 ). The frame extension is returned (step  418 ) and then the frame extension can be removed from the stack frame shadow apparatus (step  420 ). Several of these steps will be discussed below in greater detail. Within the stack frame shadow apparatus  426  are stack frame extensions for first thread  422  and for the second thread  424 . 
     FIG. 5  provides a comparison between the Java stack frame data structure  502  and the Java stack frame extension data structure  510  in the stack frame shadow apparatus  426  of FIG.  4 . The Java stack frame data structure  502  includes the pointer to the last stack frame  504 , the local variables in this stack frame  506 , and other information  508 . The Java stack frame extension data structure  510  can include the Java security privilege  512 , other variables  514 , the method name and signature for validation  516 , and the return address for validation  518 . The pointer to the Java stack frame  520  is used to map this extension entry with the JVM&#39;s stack frame  508 . 
     FIG. 6  is a flow chart of the method  600  of setting Java stack frame extension in the apparatus. First, the system must use the thread identifier to get a list of frame extension entries (step  602 ). Next, the system searches for the list of frames for matching frame entry(ies) (step  604 ). Next, the system decides whether a matching frame extension entry has been found (step  606 ). If yes, then the system will update the entry with the frame extension information and validation information (step  608 ). If not, then the system will create a blank entry and fill the blank entry in with frame extension information and validation information (step  610 ). 
     FIG. 7  is a flow chart of the method  700  of getting a Java stack frame extension located in the shadow apparatus  426 . The system first uses the thread identifier to get a list of frame extension entries (step  702 ). Next, the system searches the list of frame extensions for a matching frame entry (step  704 ). Next, the system decides whether a matching frame extension is found (step  706 ). If so, the system must validate the frame with frame extension information (step  708 ). If not, the system returns with a blank or null frame extension information (step  710 ). Once step  708  is completed, the system further decides whether the frame is valid for the particular entry (step  712 ). If not, the system returns to step  710 . If however, the frame is valid in step  712 , then the system returns with the frame extension information (step  714 ). 
     FIG. 8  illustrates the method  800  of removing the Java stack frame extension in the shadow apparatus  426 . First, the system uses a thread identifier to get a list of frame extension entries (step  802 ). Next, the system searches the list of frame extensions for a matching frame entry (step  804 ). If a matching frame extension is found (step  806 ), then the entry is removed from the list (step  808 ). If no match is found, then the system returns (step  810 ) to the caller to revert privilege. 
   It is important to note that while the present invention has been described in the context of a fully functioning data processing system, those of ordinary skill in the art will appreciate that the processes of the present invention are capable of being distributed in a form of a computer readable medium of instructions and a variety of forms and that the present invention applies equally regardless of the particular type of signal bearing media actually used to carry out the distribution. Examples of computer readable media include recordable-type media such a floppy disc, a hard disk drive, a RAM, and CD-ROMs and transmission-type media such as digital and analog communications links. 
   The description of the present invention has been presented for purposes of illustration and description, but is not limited to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiment was chosen and described in order to best explain the principles of the invention the practical application and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated.