Patent Publication Number: US-7596809-B2

Title: System security approaches using multiple processing units

Description:
CROSS REFERENCE 
   This application is a continuation-in-part of U.S. application Ser. No. 10/868,665 filed on Jun. 14, 2004, which is incorporated herein by reference in its entirety. 

   FIELD 
   This patent document generally relates to system security approaches, especially methods and systems relating to preventive measures in response to attacks to a device on a network. 
   BACKGROUND 
   Unless otherwise indicated herein, the approaches described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section. 
   As computer networks become ubiquitous, any device that is connected to the networks is susceptible to debilitating attacks, such as viruses, worms, and cracker attacks. Typical approaches to counter these attacks include firewall techniques and anti-virus programs. Firewalls generally prevent certain types of files or packets from entering a network, and anti-virus programs typically prevent files that contain virus patterns from being executed on a device or a group of devices. 
   Several types of firewall techniques exist today. Some examples include packet filter, application gateway, and proxy server. The packet filter approach inspects the control information of each packet and determines whether to accept or reject the packet based on user-defined rules. The application gateway approach applies a security mechanism to certain applications, such as FTP and Telnet servers. The proxy server approach utilizes an in-between server to intercept and inspect packets between a client application and a server on a network to which the client application submits requests to. None of these existing techniques inspects the payload data portion of each packet or handles malicious code segments that spread across packet boundaries. 
   An anti-virus program that executes on a device generally assembles incoming packets received by the device into a file before determining whether the assembled file includes certain predetermined virus patterns. In such approaches, no inspection takes place until after a file or a block of data has been assembled. For attacks that target real-time protocols, the timing requirements of the protocols would render the aforementioned assembling-before-scanning approaches essentially inoperable. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a data flow diagram of one embodiment of a system security approach; 
       FIG. 2  shows a segment of one embodiment of a data unit; 
       FIG. 3  illustrates one process that one embodiment of a system security approach follows to establish and use the automata and the state tables representative of the unwanted patterns; 
       FIG. 4  illustrates one process that one embodiment of a system security approach follows to decompress the data in a data unit; 
       FIG. 5  illustrates one process that one embodiment of a system security approach follows to identify the anomalies of the data units; 
       FIG. 6  is a block diagram that illustrates a system upon which an embodiment of the system security approaches may be implemented; 
       FIG. 7  is a block diagram of one embodiment of a content inspection co-processor; and 
       FIG. 8  is a block diagram of another embodiment of a content inspection co-processor. 
   

   DETAILED DESCRIPTION 
   System security approaches are described. In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a thorough understanding of the present invention. It will be apparent, however, to one skilled in the art that the present invention may be practiced without these specific details. 
   The general theories behind “regular expression,” “state machine,” and “automaton,” are well known in the art and will not be elaborated in detail. However, throughout this disclosure, “state machine” is used interchangeably with “state automaton”. “Wild card” generally refers to special symbols, such as a combination of the period and the asterisk (.*), that stand for zero, one, or more characters (e.g., “.*abc” refers to all patterns that end with “abc”). Each “data unit” generally refers to data that are stored in a particular memory location or a packet with a destination address. An “application” generally refers to a program or a group of programs designed for a user of a terminal or a computer system. 
   1.0 General Overview 
   The system security approaches as discussed below include methods and systems that utilize a first processing unit to split a regular expression that corresponds to a number of patterns into sub-expressions and maintain the dependency relationships among the finite automata that correspond to the sub-expressions. The methods and systems also utilize a second processing unit to move the data units through these finite automata in a sequence that is based on the dependency relationships to identify the suspected data units. The suspected data units are the ones containing content that collectively matches one or more of the aforementioned patterns. Identification of the suspected data units is based on the merged results of the finite automata. 
   2.0 System Security Approaches 
   2.1 Overview 
   An overview of system security approaches is now provided. To “secure” a system, one approach is to examine data units that enter into and depart from the system to ensure that the system is freed from invasion of unwanted codes and unauthorized accesses. The approach is based in part on the use of regular expressions, which generally refer to sets of symbols and syntactic elements used to represent certain patterns. For example, a simple regular expression, such as (a/b)t, represents the patterns “at” and “bt”. Although a well-crafted regular expression may appear concise, especially with the use of wild cards, the expression may represent many patterns and result in a state machine with many states. 
   One system security approach is also based in part on managing and manipulating the states in various state automata that are derived from the regular expressions to effectively search and match certain patterns. As more and more patterns are identified as unwanted patterns, additional steps are also needed to accelerate the searching and matching of various patterns while lessening storage requirements. 
   One embodiment of the system security approach has at least one process dedicating to generate the state automata from the regular expressions and at least one separate process dedicating to use the state automata to search for the unwanted patterns. In addition, at least one of the processes is also capable of monitoring the data units for anomalies that cannot be described with the regular expressions. 
     FIG. 1  is a data flow diagram of one embodiment of a system security approach. This embodiment includes two main processes: 1) process  102 , which is mainly carried out by dispatch engine  104 , content inspection engine  106 , and memory controller  108 , and 2) process  110 , which is mainly carried out by processing unit  112 . Process  110  generates the state automata, and process  102  searches for the suspected data units that contain the unwanted patterns, such as, without limitation, known viruses, worms, spam, illegal accesses, or any malicious codes that are represented by the state automata. These unwanted patterns can also be sound patterns, image patterns, or any other non-text based patterns, as long as they can be translated to regular expressions. Process  110  also performs functions such as, without limitation, decompressing the data contained in data units and monitoring data units for any irregularity that cannot be described by regular expressions. 
     FIG. 2  shows data unit segment  200 , which is a segment of one embodiment of a data unit. Data unit segment  200  mainly includes header field  202  and payload field  210 . Header field  202  contains additional fields, such as, without limitation, type field  204 , length field  206 , and command field  208 . Payload field  210  contains textual data, multimedia data, and/or control information. 
   In this embodiment, type field  204  contains information indicative of the various types of data units. For example, payload field  210  of the first type of a data unit may contain the regular expressions representing a partial or an entire unwanted pattern or the information for configuring process  102  or process  110 . On the other hand, payload field  210  of the second type of a data unit may contain data that are to be inspected for unwanted patterns and anomalies by process  102 . In some instances, the data in the second type of the data unit are also manipulated by process  110 . Thus, a process having received the data unit can use the information in type field  204  to determine whether the data unit is the first type or the second type and take actions accordingly. Throughout the disclosure, the first type and the second type of the data units discussed above are generally referred to as the “system-type” and the “user-type” data units, respectively. 
   Length field  206  contains the length information of the data in payload field  210 , and command field  208  contains the instructions for processing unit  112 , memory controller  108 , and content inspection engine  106  to perform certain tasks. For example, the instructions may cause processing unit  112  to decompress the data in payload field  210  or check the data for anomalies. Each command field  208  can contain one or more instructions, and the instructions can be directed to one or more components. In other words, command field  208  can contain a single instruction for a single component, such as processing unit  112 , multiple instructions all for a single component, or multiple instructions for multiple components, such as some instructions for processing unit  112 , others for memory controller  108 , and yet others for content inspection engine  106 . 
   In one embodiment, dispatch engine  104  serves a common gateway to application  100 . Specifically, based on the information in the header fields and payload fields of the data units dispatch engine  104  receives, dispatch engine  104  distributes the data units to content inspection engine  106 , memory controller  108 , and processing unit  112  for further processing. Generally, content inspection engine  106  is dedicated to identifying the suspected data units with the data that collectively match the unwanted patterns. Processing unit  112 , on the other hand, performs tasks such as, without limitation, decompressing the data in the payload fields of the data units and monitoring the data units for irregularities or anomalies. Moreover, dispatch engine  104  also organizes the results from content inspection engine  106  and processing unit  112  and passes the organized results to application  100 . The subsequent discussions will further elaborate the interactions among the aforementioned components. 
   2.2 Establishment and Use of Automata and State Tables by Multiple Processing Units 
     FIG. 3  illustrates one process that one embodiment of a system security approach follows to establish and use the automata and the state tables representative of the unwanted patterns. In block  300 , if dispatch engine  104  as shown in  FIG. 1  recognizes the received data unit to be a system-type data unit based on the information in type field  204  as shown in  FIG. 2 , then dispatch engine  104  further examines command field  208  of the data unit to determine whether the data unit contains the regular expressions that need to be converted or the information relating to the already converted automata and state tables. This process of converting the regular expressions to the automata and state tables is also referred to as the “compiling” process. 
   If command field  208  of the data unit includes instructions for processing unit  112  to generate the automata and state tables, then dispatch engine  104  sends the data unit to processing unit  112  in block  304 , where processing unit  112  compiles the data in payload field  210  of the data unit. In some instances, processing unit  112  detects compilation errors in block  306 . For instance, if the syntax of the regular expressions is inaccurate, then the state automata and state tables cannot be generated. Another compilation error occurs if the resulting state automata and state tables would occupy more memory locations than the memory capacity allotted for process  102 , process  110 , or both of the processes. In one implementation, processing unit  112  reports the compilation errors to application  100  via dispatch engine  104  in block  310 . 
   On the other hand, if command field  208  of the data unit includes instructions for memory controller  108  to store and manage the information relating to the already converted automata and state tables, then dispatch engine  104  sends the data unit to memory controller  108  in block  308  so that the data in payload field  210  of the data unit are stored. In one implementation, memory controller  108  loads the converted automata and state tables into memory locations for content inspection engine  106  to access prior to or at the initialization of content inspection engine  106 . In some instances, memory controller  108  detects loading errors. For example, one type of loading error occurs if the stored data become corrupted. 
   If dispatch engine  104  recognizes the received data unit to be a user-type data unit based on the information in type field  204  in block  300  and if command field  208  includes instructions for content inspection engine  106  to search for and identify the suspected data units, then dispatch engine  104  sends the data unit to content inspection engine  106  for the examination of the data in payload field  210  of the data unit in block  312 . Content inspection engine  106  sends its search results to application  100  in block  310 . 
   2.3 Decompression of Data 
   When the received data unit is a user-type data unit, the data unit could contain compressed data. For example, if application  100  is an email application, then the data unit could contain data that are representative of the compressed attachment sent by the email application.  FIG. 4  illustrates one process that one embodiment of a system security approach follows to decompress the data in a data unit. 
   In particular, prior to sending the data unit to content inspection engine  106  in block  410 , dispatch engine  104  examines command field  208  and payload field  210  of the data unit in block  400 . In one implementation, if command field  208  includes the instructions for processing unit  112  to decompress the data in payload field  210 , then dispatch engine  104  sends the data unit to processing unit  112  in block  404 , where processing unit  112  decompresses the data according to the instructions. In some instances, processing unit  112  detects decompression errors in block  406 . For example, a decompression error occurs if the processing unit  112  does not have access to the required memory capacity for performing the mathematical computations. Another decompression error occurs if processing unit  112  does not have all the information, such as the password, to perform the decompression. In one implementation, processing unit  112  reports the decompression errors to application  100  via dispatch engine  104  in block  408  and does not proceed to inspect the data unit for unwanted patterns. 
   2.4 Detection of Anomalies 
   Furthermore, when the received data units are user-type data units, the data units could contain data that would bring undesirable consequences to the receiving system but cannot be described using regular expressions. For example, in a denial-of-service attack, the resources of a receiving system are exhausted to handle the volume of the received data units and not the unwanted patterns that are resident in the data units.  FIG. 5  illustrates one process that one embodiment of a system security approach follows to identify the anomalies of the data units. 
   Prior to sending the data unit to content inspection engine  106  in block  510 , dispatch engine  104  examines command field  208  and payload field  210  of the data unit in block  500 . In one implementation, if command field  208  includes the instructions for processing unit  112  to look for anomalies, then dispatch engine  104  sends the data unit to processing unit  112  in block  504 , where processing unit  112  analyzes certain characteristics of the received data units according to the instructions and certain anomaly policies. As an illustration, one anomaly policy can be to limit the receipt and processing of a threshold number of data units containing the same data in their respective payload fields. Thus, as processing unit  112  tracks the number of the data units meeting the criteria of the anomaly policy pursuant to the instructions, after the number exceeds the threshold number in block  506 , processing unit  112  responds to the detected anomaly (e.g., rejecting the subsequently received data units with the same data) and/or reports the detected anomaly to application  100 . 
   Although not explicitly shown in  FIG. 5 , the aforementioned blocks  506  and  508  can also be executed after the inspection of the content of the data units. In other words, in one implementation, block  510  can be executed prior to the anomaly detection process, or before block  500 . After block  510  is executed, one embodiment of processing unit  112  rectifies certain detected unwanted patterns or anomalies by placing either zeroes or a predetermined data patterns in the data units. For example, if the data units contain unwanted patterns, commands that could cause instability to the receiving system, or codes that violate any communication and operation protocols, processing unit  112  not only detects such patterns and anomalies, but can also replace them with “harmless” patterns, such as all zeroes, which are patterns that would not cause undesirable consequences to the receiving system. 
   It should be noted that the anomaly policy discussed above can be configurable via the system-type data units. The configuration would be similar to the compilation process shown in  FIG. 3 . Specifically, processing unit  112  can configure the anomaly policy based on the data in the command fields and payload fields of the data units. 
   3.0 Example System Structure 
     FIG. 6  is a block diagram that illustrates a system  600  upon which an embodiment of the system security approaches may be implemented. Specifically, system  600  includes a processor  604 , content inspection co-processor (“CICP”)  602 , which dedicates to perform the content inspection tasks. Processor  604  corresponds to processing unit  112  as shown in  FIG. 1 , and CICP  602  corresponds to dispatch engine  104 , memory controller  108 , and content inspection engine  106  as shown in  FIG. 1 .  FIG. 7  is a block diagram of an embodiment of CICP  602 . 
     FIG. 8  is a block diagram of another embodiment of CICP  602 . Processing unit  112  is a part of CICP  602  in this implementation. In other words, this embodiment of CICP  602  includes two processing units, namely the processing unit and the content inspection engine. 
   CICP can be implemented as an application-specific integrated circuit (“ASIC”), programmed in a programmable logic device, or even as a functional unit in a system-on-chip (“SOC”). In one implementation, CICP  602  communicates with processor  604  via bridge  608  and memory bus  606 . Alternatively, CICP  602  can communicate directly with processor  604  (this direction communication channel is not shown in  FIG. 6 ), if processor  604  provides appropriate interfaces for such communication. 
   Processor  604  can either be a general purpose processor or a specific purpose processor. Some examples of a specific purpose processor are processors that are designed for, without limitation, signal processing, mobile computing, and multimedia related applications. Specific purpose processors often include interfaces that other external units can directly connect. For instance, such a specific purpose processor may include one or more memory interfaces that either various types of memories can connect to or a co-processing unit, such as CICP  602  can connect to. 
   Various types of memory modules can be placed inside of CICP  602  or coupled to memory bus  606  or CICP  602  to provide temporary storage for CICP  602 . Some of these memory modules also provide temporary storage for processor  604 . Some examples of the memory modules include various types of RAM and flash memory. Additionally, one or more of the components illustrated in  FIG. 6  can be added (e.g., display device), combined (e.g., CICP  602  and processor  604  can reside on one SOC), or further divided (e.g., bridge  608  can be further divided into a processor bridge, a bus controller, and a memory controller) and still remain within the claimed scope of the system security approaches. 
   4.0 Extensions and Alternatives 
   In the foregoing specification, the invention has been described with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.