Abstract:
A computer that self-administers operating in restricted and unrestricted operating modes boots from a main processor and operates normally in the unrestricted operating mode and operates from an alternate processor in a security module in the restricted operating mode. The alternate processor may communicate directly with peripheral devices such as a display controller and keyboard. Because the main processor is not used and may not even be started in the restricted operating mode, viruses, shims, and other related attacks are virtually eliminated. In one embodiment, the security module may operate as a PCI bus master when in the restricted operating mode.

Description:
BACKGROUND 
       [0001]    In many cases, it is desirable to restrict the operation of a computer to known modes. For example, a parent may wish to restrict gaming time while allowing word processing. In another example, a company may wish to limit the use of an expensive peripheral, such as a 3-D printer, to only authorized users. In another example, a pay-per-use computer may have an unlimited use mode when the terms of an associated contract are satisfied and a restricted use mode that only allows input of additional usage time or points when terms of the associated contract are not met. 
         [0002]    In the latter case, a low, subsidized, initial price of a computer may require a contractual obligation to recoup an underwriters investment. Because contractual terms may have already been intentionally disregarded, a user may be inclined to attempt to defeat or evade the restricted use mode. Doing so may allow the user to enjoy the benefits of the computer without meeting contractual terms, such as payment of monthly subscription fees, to the detriment of the underwriter. 
       SUMMARY 
       [0003]    A computer may be required to self-administer a restricted-use mode when a user is able to isolate the computer from other means of sanctioning, such as a computer network or Internet Service Provider (ISP). Therefore, the circuitry involved in the restricted use mode can be expected to attract hacking attempts by unscrupulous users. An attack profile for defeating restricted mode operation is directly related to the number of components that are active, particularly those involved in enforcing such operation. The attack profile may be dramatically reduced when a security module used for metering and enforcement acts as a bus master, for example, on a peripheral component interconnect (PCI) bus, to directly communicate with a limited number of required components. For example, a security module may directly control a display interface and keyboard controller to provide a minimal user interface to allow entry of data to restore full services. 
         [0004]    By avoiding use of the computer&#39;s main processor, main memory disk drives, other chipset components, etc., most conventional attacks, such as buffer overflow attacks or memory swapping, are immediately eliminated. Even though the security module may become the focus of attacks, this also allows a design and manufacturing focus on protection of the security module rather than trying to protect every hardware and software aspect of the computer. The security module may be a standalone component or may be integrated into a communication or processing circuit, such as one of the chipset components common in known computer architectures. 
         [0005]    The use of pre-boot direct device communication may be used to in many embodiments. In one embodiment, basic user interface and communication functions may be supported without intervention from a main processor of the computer. In another embodiment, the direct device communication may be used in conjunction with system checks verify the security and health of the computer. Following such checks, the direct device communication may be used to unlock those same components for normal operation supporting a normal boot process with a standard basic input/output system (BIOS). 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a simplified and exemplary block diagram of a computer system suitable for use with peer-to-peer communication for secure operation; 
           [0007]      FIG. 2  is a simplified and exemplary block diagram of a security module; and 
           [0008]      FIG. 3  is a flow chart of an exemplary method of executing peer-to-peer communication for secure operation. 
       
    
    
     DETAILED DESCRIPTION 
       [0009]    Although the following text sets forth a detailed description of numerous different embodiments, it should be understood that the legal scope of the description is defined by the words of the claims set forth at the end of this disclosure. The detailed description is to be construed as exemplary only and does not describe every possible embodiment since describing every possible embodiment would be impractical, if not impossible. Numerous alternative embodiments could be implemented, using either current technology or technology developed after the filing date of this patent, which would still fall within the scope of the claims. 
         [0010]    It should also be understood that, unless a term is expressly defined in this patent using the sentence “As used herein, the term ‘______’ is hereby defined to mean . . . ” or a similar sentence, there is no intent to limit the meaning of that term, either expressly or by implication, beyond its plain or ordinary meaning, and such term should not be interpreted to be limited in scope based on any statement made in any section of this patent (other than the language of the claims). To the extent that any term recited in the claims at the end of this patent is referred to in this patent in a manner consistent with a single meaning, that is done for sake of clarity only so as to not confuse the reader, and it is not intended that such claim term by limited, by implication or otherwise, to that single meaning. Finally, unless a claim element is defined by reciting the word “means” and a function without the recital of any structure, it is not intended that the scope of any claim element be interpreted based on the application of 35 U.S.C. § 112, sixth paragraph. 
         [0011]    Much of the inventive functionality and many of the inventive principles are best implemented with or in software programs or instructions and integrated circuits (ICs) such as application specific ICs. It is expected that one of ordinary skill, notwithstanding possibly significant effort and many design choices motivated by, for example, available time, current technology, and economic considerations, when guided by the concepts and principles disclosed herein will be readily capable of generating such software instructions and programs and ICs with minimal experimentation. Therefore, in the interest of brevity and minimization of any risk of obscuring the principles and concepts in accordance to the present invention, further discussion of such software and ICs, if any, will be limited to the essentials with respect to the principles and concepts of the preferred embodiments. 
         [0012]    With reference to  FIG. 1 , an exemplary system for implementing the claimed method and apparatus includes a general purpose computing device in the form of a computer  110 . Components shown in dashed outline are not technically part of the computer  110 , but are used to illustrate the exemplary embodiment of  FIG. 1 . Components of computer  110  may include, but are not limited to, a main processor  120 , a system memory  130 , a memory/graphics interface  121 , also known as a Northbridge chip, and an I/O interface  122 , also known as a Southbridge chip. A memory  130  and a graphics processor  190  may be coupled to the memory/graphics interface  121 . A monitor  191  or other graphic output device may be coupled to the graphics processor  190 . 
         [0013]    A series of system busses may couple various these system components including a high speed system bus  123  between the main processor  120 , the memory/graphics interface  121  and the I/O interface  122 , a front-side bus  124  between the memory/graphics interface  121  and the system memory  130 , and an advanced graphics processing (AGP) bus  125  between the memory/graphics interface  121  and the graphics processor  190 . The system bus  121  may be any of several types of bus structures including, by way of examples and not limitation, such architectures include Industry Standard Architecture (ISA) bus, Micro Channel Architecture (MCA) bus and Enhanced ISA (EISA) bus. As system architectures evolve, other bus architectures and chip sets may be used but often generally follow this pattern. For example, companies such as Intel and AMD support the Intel Hub Architecture (IHA) and the Hypertransport architecture, respectively. 
         [0014]    Computer  110  typically includes a variety of computer readable media. Computer readable media can be any available media that can be accessed by computer  110  and includes both volatile and nonvolatile media, removable and non-removable media. By way of example, and not limitation, computer readable media may comprise computer storage media and communication media. Computer storage media includes both volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information such as computer readable instructions, data structures, program modules or other data. Computer storage media includes, but is not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVD) or other optical disk storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired information and which can accessed by computer  110 . Communication media typically embodies computer readable instructions, data structures, program modules or other data in a modulated data signal such as a carrier wave or other transport mechanism and includes any information delivery media. The term “modulated data signal” means a signal that has one or more of its characteristics set or changed in such a manner as to encode information in the signal. By way of example, and not limitation, communication media includes wired media such as a wired network or direct-wired connection, and wireless media such as acoustic, RF, infrared and other wireless media. Combinations of the any of the above should also be included within the scope of computer readable media. 
         [0015]    The system memory  130  includes computer storage media in the form of volatile and/or nonvolatile memory such as read only memory (ROM)  131  and random access memory (RAM)  132 . The system ROM  131  may contain permanent system data  143 , such as identifying and manufacturing information. In some embodiments, a basic input/output system (BIOS) may also be stored in system ROM  131 . RAM  132  typically contains data and/or program modules that are immediately accessible to and/or presently being operated on by main processor  120 . By way of example, and not limitation,  FIG. 1  illustrates operating system  134 , application programs  135 , other program modules  136 , and program data  137 . 
         [0016]    The I/O interface  122  may couple the system bus  123  with a number of other busses  126 ,  127  and  128  that couple a variety of internal and external devices to the computer  110 . A serial peripheral interface (SPI) bus  128  may connect to a basic input/output system (BIOS) memory  133  containing the basic routines that help to transfer information between elements within computer  110 , such as during startup. 
         [0017]    A security module  129  may also be coupled to the I/O controller  122  via the SPI bus  126 . In other embodiments, the security module  129  may be connected via any of the other busses available in the computer  110 . In a pay-per-use business model, the security module  129  may meter usage, support booting from a known BIOS, and monitor compliance to metering-related policies. When tampering or other suspicious behavior is observed that may indicate attempts to circumvent pay-per-use operation, the security module  129  may sanction the computer by forcing operation in a limited function mode. 
         [0018]    A super input/output chip  160  may be used to connect to a number of ‘legacy’ peripherals, such as floppy disk  152 , keyboard/mouse  162 , and printer  196 , as examples. The super I/O chip  122  may be connected to the I/O interface  121  with a low pin count (LPC) bus, in some embodiments. The super I/O chip is widely available in the commercial marketplace. 
         [0019]    In one embodiment, bus  128  may be a Peripheral Component Interconnect (PCI) bus, or a variation thereof, may be used to connect higher speed peripherals to the I/O interface  122 . A PCI bus may also be known as a Mezzanine bus. Variations of the PCI bus include the Peripheral Component Interconnect-Express (PCI-E) and the Peripheral Component Interconnect-Extended (PCI-X) busses, the former having a serial interface and the latter being a backward compatible parallel interface. In other embodiments, bus  128  may be an advanced technology attachment (ATA) bus, in the form of a serial ATA bus (SATA) or parallel ATA (PATA). 
         [0020]    The computer  110  may also include other removable/non-removable, volatile/nonvolatile computer storage media. By way of example only,  FIG. 1  illustrates a hard disk drive  140  that reads from or writes to non-removable, nonvolatile magnetic media. Removable media, such as a universal serial bus (USB) memory  152  or CD/DVD drive  156  may be connected to the PCI bus  128  directly or through an interface  150 . Other removable/non-removable, volatile/nonvolatile computer storage media that can be used in the exemplary operating environment include, but are not limited to, magnetic tape cassettes, flash memory cards, digital versatile disks, digital video tape, solid state RAM, solid state ROM, and the like. 
         [0021]    The drives and their associated computer storage media discussed above and illustrated in  FIG. 1 , provide storage of computer readable instructions, data structures, program modules and other data for the computer  110 . In  FIG. 1 , for example, hard disk drive  140  is illustrated as storing operating system  144 , application programs  145 , other program modules  146 , and program data  147 . Note that these components can either be the same as or different from operating system  134 , application programs  135 , other program modules  136 , and program data  137 . Operating system  144 , application programs  145 , other program modules  146 , and program data  147  are given different numbers here to illustrate that, at a minimum, they are different copies. A user may enter commands and information into the computer  20  through input devices such as a mouse/keyboard  162  or other input device combination. Other input devices (not shown) may include a microphone, joystick, game pad, satellite dish, scanner, or the like. These and other input devices are often connected to the processing unit  120  through one of the I/O interface busses, such as the SPI  126 , the LPC  127 , or the PCI  128 , but other busses may be used. In some embodiments, other devices may be coupled to parallel ports, infrared interfaces, game ports, and the like (not depicted), via the super I/O chip  160 . 
         [0022]    The computer  110  may operate in a networked environment using logical connections to one or more remote computers, such as a remote computer  180  via a network interface controller (NIC)  170 . The remote computer  180  may be a personal computer, a server, a router, a network PC, a peer device or other common network node, and typically includes many or all of the elements described above relative to the computer  110 . The logical connection depicted in  FIG. 1  may include a local area network (LAN), a wide area network (WAN), or both, but may also include other networks. Such networking environments are commonplace in offices, enterprise-wide computer networks, intranets and the Internet. 
         [0023]    In some embodiments, the network interface may use a modem (not depicted) when a broadband connection is not available or is not used. It will be appreciated that the network connection shown is exemplary and other means of establishing a communications link between the computers may be used. 
         [0024]      FIG. 2  depicts a security module  200 , similar to the security module  129  of  FIG. 1 . The exemplary embodiment of the security module  200  is but one example of a security module suitable for use in this application. The security module  200  may be a standalone component. In other embodiments, the security module  200  may be incorporated in another component, for example, a chipset component such as the I/O interface  122 . The I/O interface  122  is strategically located on each of the major system busses and allows almost transparent access to most of the major systems and components of a computer as shown in  FIG. 1 . 
         [0025]    The security module  200  may have several functions. One function may be to represent the interests of an underwriter with a financial stake in the computer by requiring that the underwriter&#39;s contractual terms are met. Those terms may include payment for use of the computer in the form of a subscription or metered usage time. The security module  200  may include metering circuitry (not depicted) and a memory for saving stored value. The security module  200  may or may not have integrated BIOS memory. 
         [0026]    The security module  200  may also include circuitry and applications associated with its second function of enforcing a limited function mode of operation when the contractual terms are not met. The goal of the limited, or restricted, mode of operation is to deny the user beneficial use of the computer while supporting enough functionality to restore normal operation by updating the subscription or adding resources to the stored value balance. The use of direct communication for restricted mode operation may be one aspect of this enforcement function. As shown in  FIG. 2 , a serial peripheral interface (SPI)  202  may be coupled to a processor  204  and a nonvolatile memory  206 . The SPI interface  202  may be connected to an SPI master device, such as I/O interface  122  of  FIG. 1 . In one embodiment, the processor  204  may be coupled to the nonvolatile memory  206  via a bus  208  that may be another serial peripheral interface or another kind of memory bus. In another embodiment, the SPI interface  202  may connect to both the processor and the nonvolatile memory  206 . 
         [0027]    The processor  204  may be coupled to other exemplary bus interfaces such as an low pin count (LPC) interface  214 , a general purpose input/output (GPIO) interface  216 , or a PCI interface  218 . In other embodiments, more or fewer busses may be connected to the processor  204 . The nonvolatile memory  206  may include partitions for a first BIOS  222 , a second BIOS  224 , as well as executable processor code  226  used by the processor  204 . A mode flag  228  may provide a secure way of persisting the operating state of the computer, that is, restricted or unrestricted, following the next reset. 
         [0028]    A power OK pin  210  may be used to monitor or set a signal indicating that the power supply is stable. As will be discussed, this signal may also be used to selectively disable some circuits. A reset output  212  may be used by the processor  204  to cause an interruption in operation of a computer incorporating the security device  200 , such as computer  110  of  FIG. 1 . 
         [0029]    The processor  204  may be a single-chip processor such as an ARM processor from ARM Ltd of Cambridge, UK, although similar processors from Intel and Freescale Semiconductor are also available. The nonvolatile memory  206  may be a flash technology device widely available in the commercial marketplace. 
         [0030]    In operation, when reset activity is detected, for example, when a Power OK signal  210  transitions from inactive to active, the processor  204  may read the mode flag  228  to determine how to start the computer  110 . If the mode flag indicates normal operation, the processor  204  may allow access to a BIOS designated for normal operation, for example, BIOS  222 . However, when the mode flag  228  indicates operation is to be in the restricted mode, the processor  204  may block access to the normal boot BIOS and may instead cause the computer  110  to boot from a secondary BIOS  224 . The secondary BIOS  224  may not activate all the functions of the computer  10 . In one embodiment, the BIOS  224  is code only used by the processor  204  or a link to the processor code  226 . In this embodiment, with operation designated in the restricted mode, the processor  204  may take over operation of the computer  110 . 
         [0031]    In order to accomplish this, the processor  204 , responsive to executable commands in the alternate BIOS  224  or processor code  226 , may create a direct link to various peripheral devices needed for minimal functionality. Such minimal functionality may include access to the graphics controller  190  to enable output to the monitor  191  and to the keyboard/mouse  162 , either directly or through the Super I/O chip  160 . Minimal functionality may also include a direct connection to the network interface  170  for communication with a remote computer  180 , or to access a network accessible user input device, such as a terminal (not depicted). 
         [0032]    Direct connection does not necessarily mean without any intervening circuitry but rather is intended to denote that data is passed without any intervention or activity on part of the main processor  120 . Because the main processor  120  is bypassed, the associated peripherals, firmware, and software associated with activating and operating the main processor  120  are also unnecessary and may also be bypassed or not even started. The degree to which the main processor  120  and other devices, such as disk drives, the Northbridge, etc. are not activated is a design decision, but each boot activity from a normal boot that is not performed, contributes to lowering the overall attack profile of the computer  110 . 
         [0033]    The smallest possible attack profile may then be provided by only activating the minimal number of components required to conditions for unrestricted operation. In one embodiment, the minimal number of components may be use of enough of the display  191  to support a prompt and enough of an input capability, such as keyboard/mouse  162  to support entry of an unlock code or provisioning packet. Other useful peripherals for entry of provisioning information may be removable media such as floppy disk  152 , CD/DVD  156 , or USB port  152  to support a flash drive. Connection to remote computer  180  via network interface  170  may also provide access to restoration data such as a provisioning packet. 
         [0034]    Not starting the main processor  120  also implies that any attack targeted at the operating system  134  or applications  135 , including viruses, would be not be effective, since the OS  134  and applications  135  are not activated. 
         [0035]    In one embodiment that disables the main processor  120 , the processor  204  may have Power OK output  210  connected to a Power OK input (not depicted) on the main processor  120 . When the processor  204  determines that operation is to be in the restricted operation mode, the Power OK output  210  may be reset, causing the main processor to not start, or if operating, to cease operation, as if the power were shutting down. Other circuits that respond to the Power OK signal may be similarly disabled when the processor  204  determines operation in the restricted mode. For example, a non-removable non-volatile memory controller  140 , such as a disk controller, may be prevented from starting when operation is in the restricted mode by controlling the Power OK signal. 
         [0036]    After determining that the computer  110  is to be operated in the restricted mode, the direct link may be established between the security module  200  and another peripheral or peripheral controller, such as graphics processor  190 . The security module  200  may operate as a bus master when communicating over the PCI bus  128 . Operation as a PCI bus master allows the security module  200  perform known control functions to select a target component from among connected PCI devices and carry on bidirectional communication with the targeted component. When other busses are used, appropriate controls and protocols may be used. For example, even though the protocol may dictate certain signal levels and timing, the message traffic may follow other standard formats such as XML, to allow standardization and convenience for development, debugging, and maintenance of inter-component messaging. 
         [0037]    Another risk for restricted mode operation may be substitution of components, either to try to circumvent control by the security module  200  or to strip parts from the computer for resale. Both of these threats may be addressed by cryptographic verification that the correct components are present and functional, or at least functional enough to respond to a challenge issued by the security module  200 . While in a secure manufacturing environment, or in another trusted setting, components installed in the computer may be given secret keys that can be used for one-way or mutual verification. Such mutual verification between the security module  200  and other components may be performed as part of each boot, only when tampering is suspected, when in the restricted operating mode, or a combination of these. 
         [0038]      FIG. 3 , a method of using peer-to-peer communication for secure operation of a computer, is discussed and described. At block  302 , when a computer, such as computer  110  of  FIG. 1 , is started, an early process may activate a security module, such as security module  129  of  FIG. 1 . Optionally, at block  303 , certain components may be designated to start in a locked mode. The locked mode setting of components such as the I/O interface  122 , the memory/graphics interface  121 , the network interface  170 , the processor  120 , etc., may further hinder attempts to bypass security measures taken at startup. Components started in the locked mode may support normal operating functions after being unlocked by the security module  129 . 
         [0039]    At block  304 , the security module  129  may determine whether the computer should be activated in a normal, unrestricted operating mode or a restricted operating mode. This determination may be made by checking the state of a memory location, such as mode flag  228  of  FIG. 2 . A flag value of zero may indicate normal operation and a flag value of one may indicate restricted operation. As mentioned above, the goal of restricted operation is to limit use of the computer to only those functions required to bring the computer back into compliance with contractual terms of operation, e.g. updating a subscription end date or adding usage time to a stored value balance in the security module  129 . 
         [0040]    When, at block  304 , the determination is made that operation should be in the unrestricted mode, the “unrestricted” branch from block  304  may be taken to block  305 . If the component locking function at block  303  was active, at block  305  an unlock message may be sent to each of those components previously locked. A single message may be broadcast to each component on a single bus or a series of independent messages may be sent to each locked component. In one embodiment a security module  200  may hold the power OK line  210  to the processor  120  until all components acknowledge being unlocked, at which point the power OK line  120  may be released and the processor  120  can begin a normal boot sequence. At block  306 , the security module  129  may allow booting from a standard BIOS and for operation to proceed under normal conditions, that may include usage metering and tamper monitoring. If, during the course of operation, conditions change, such as a metering balance going to zero, the mode flag  228  may be set and a reset forced on the computer  110  to send operation back to block  302 . 
         [0041]    When, at block  304 , the determination is made that a condition exists that indicates operation in a restricted mode, such as the mode flag  228  being set or a zero stored value balance, the “restricted” branch from block  304  may be taken to block  308 . At block  308 , the security module  129  may block execution of the normal boot process. In one embodiment, the security module  129  may block access to the normal boot BIOS  222  and instead use the security module&#39;s own internal processor  204  to support the restricted mode operation operating from an alternate BIOS  224  or from executable code  226  used for the security module&#39;s normal execution. If, at block  303 , components were started in the locked mode, those components required for restricted operation may be unlocked. For example, the memory/graphics interface  121  and the network interface  170  may be unlocked as needed. 
         [0042]    Part of the restricted mode operation may include verification of one or more peripheral devices through a cryptographic challenge response function. For example, the security module  129  may send an encrypted nonce to a graphics processor  190  and receive back the decrypted nonce and an encrypted device identifier. If, at block  310 , the peripheral device verification passes, the past branch from block  310  may be taken to block  312 . 
         [0043]    At block  312 , the security module  129  may send a message, and some embodiments an encrypted message, to the graphics controller  190  or another device capable of supporting user interface, such as a TDD hearing impaired interface (not depicted). The message may prompt a user to enter an unlock code or token, such as a flash disk, to recover from the condition that caused operation in the restricted mode. In some cases the token may be available via the network interface  170  from a remote device, such as remote computer  180 . In such a circumstance the network interface  170  may be activated and controlled directly from the security module  129 . 
         [0044]    At block  314 , the security module  129  received a requested data and at block  316  determine if the data is sufficient to allow restoration of full operation. If so, the “yes” branch from block  316  may be taken to block  318  where the mode flag  228  may be cleared, or otherwise set to unrestricted, and the computer may be reset, for example by activating the reset output  212  of the security module  129 . In another embodiment, components locked at block  303  may be unlocked and operation may continue through a normal boot. If, at block  316  the data does not satisfy the requirements for restoration of operation, the “no” branch from block  316  may be taken to block  312  and the user prompted to reenter the unlock code or other restoration data. 
         [0045]    At block  310 , if the peripheral device verification fails, indicating physical tampering with the device or a catastrophic failure, the user may not be allowed to enter an unlock code. There may be little or no reason to allow a user to try to restore normal operation to a computer that is either damaged or intentionally tampered because subsequent operation may not support accurate metering or other security monitoring. Execution may follow the “failed” branch from block  310  to block  320  where the mode flag  228  may be set (or re-set) to the restricted mode of operation and the computer forced into a reset returning execution to block  302 . 
         [0046]    By disabling virtually all the major functions of a computer by bypassing a main processor and using a secondary processor to support direct, encrypted communication between the secondary processor and selected peripheral devices, the risk of overriding a restricted operating mode may be significantly reduced. Such a strategy may offer a significant incentive to potential underwriters to support a pay-per-use business model. Because the execution environment for the restricted mode operation is almost completely separate from that of normal operation, the likelihood of an easily propagated attack, such as through scripting, can also be lowered significantly. 
         [0047]    Although the foregoing text sets forth a detailed description of numerous different embodiments of the invention, it should be understood that the scope of the invention is defined by the words of the claims set forth at the end of this patent. The detailed description is to be construed as exemplary only and does not describe every possibly embodiment of the invention because describing every possible embodiment would be impractical if not impossible. Numerous alternative embodiments could be implemented, using either current technology or technology developed after the filing, date of this patent, which would still fall within the scope of the claims defining the invention. 
         [0048]    Thus, many modifications and variations may be made in the techniques and structures described and illustrated herein without departing from the spirit and scope of the present invention. Accordingly, it should be understood that the methods and apparatus described herein are illustrative only and are not limiting upon the scope of the invention.