Abstract:
When a user-mode inpage error occurs after the system has booted up, the inpage error handling method attempts to prevent future crashes by repairing the faulting file. The fault may be a corrupt file or may be a disk I/O problem. The next time the now-repaired file is requested, execution should continue normally.

Description:
BACKGROUND 
     Some operating systems handle corrupted system files “gracefully.” If the undamaged portion of the file was still usable; failures occurred only when the corruption directly affected the code path taken in the binary and repair was a simple copy operation of a pristine copy of the same file, often from DllCache. In future operating systems, the system may become more brittle. Code Integrity (CI) may prevent code from being paged in once corruption is detected, even if only a single bit is corrupted. This corruption can be attributed to malicious activity or due to simple bit rot on the disk. These failures may cause user-mode crashes when inpage attempts fail. It is speculated that these errors will happen after extended use of the disk. In addition to the code integrity issue, inpage errors occur when bad blocks prevent the system from reading code from the disk. 
     SUMMARY 
     When a user-mode inpage error occurs after the system has booted up, the inpage error handler attempts to prevent future crashes by repairing the faulting file. The fault may be a corrupt file or may be a disk I/O problem. The next time the now-repaired file is requested, execution should continue normally. 
    
    
     
       DRAWINGS 
         FIG. 1  is a block diagram of a computing system that may operate in accordance with the claims; 
         FIG. 2  is a high level illustration of a method of detecting and correcting corrupted pages used by an operating system; 
         FIG. 3  is an illustration of some sample displays that may be created such as the displays  220  in  FIG. 2 ; 
         FIG. 4  is an illustration of the user exchange for the method; 
         FIG. 5  is a layered view of the steps leading up to the generation of the types of inpage exceptions handled by the inpage error handler; 
         FIG. 6  is an illustration of the inpage error handling flow; 
         FIG. 7  is an illustration of the lightweight check; and 
         FIG. 8  illustrates a heavier check. 
     
    
    
     DESCRIPTION 
     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 patent. 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. 
     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. 
       FIG. 1  illustrates an example of a suitable computing system environment  100  on which a system for the steps of the claimed method and apparatus may be implemented. The computing system environment  100  is only one example of a suitable computing environment and is not intended to suggest any limitation as to the scope of use or functionality of the method of apparatus of the claims. Neither should the computing environment  100  be interpreted as having any dependency or requirement relating to any one or combination of components illustrated in the exemplary operating environment  100 . 
     The steps of the claimed method and apparatus are operational with numerous other general purpose or special purpose computing system environments or configurations. Examples of well known computing systems, environments, and/or configurations that may be suitable for use with the methods or apparatus of the claims include, but are not limited to, personal computers, server computers, hand-held or laptop devices, multiprocessor systems, microprocessor-based systems, set top boxes, programmable consumer electronics, network PCs, minicomputers, mainframe computers, distributed computing environments that include any of the above systems or devices, and the like. 
     The steps of the claimed method and apparatus may be described in the general context of computer-executable instructions, such as program modules, being executed by a computer. Generally, program modules include routines programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. The methods and apparatus may also be practiced in distributed computing environments where tasks are performed by remote processing devices that are linked through a communications network. In a distributed computing environment, program modules may be located in both local and remote computer storage media including memory storage devices. 
     With reference to  FIG. 1 , an exemplary system for implementing the steps of the claimed method and apparatus includes a general purpose computing device in the form of a computer  110 . Components of computer  110  may include, but are not limited to, a processing unit  120 , a system memory  130 , and a system bus  121  that couples various system components including the system memory to the processing unit  120 . The system bus  121  may be any of several types of bus structures including a memory bus or memory controller, a peripheral bus, and a local bus using any of a variety of bus architectures. By way of example, and not limitation, such architectures include Industry Standard Architecture (ISA) bus, Micro Channel Architecture (MCA) bus, Enhanced ISA (EISA) bus, Video Electronics Standards Association (VESA) local bus, Peripheral Component Interconnect (PCI) bus also known as Mezzanine bus, and the Peripheral Component Interconnect-Express (PCI-E). 
     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. 
     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 . A basic input/output system  133  (BIOS), containing the basic routines that help to transfer information between elements within computer  110 , such as during start-up, is typically stored in ROM  131 . RAM  132  typically contains data and/or program modules that are immediately accessible to and/or presently being operated on by processing unit  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 . 
     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, a magnetic disk drive  151  that reads from or writes to a removable, nonvolatile magnetic disk  152 , and an optical disk drive  155  that reads from or writes to a removable, nonvolatile optical disk  156  such as a CD ROM or other optical media. 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. The hard disk drive  141  is typically connected to the system bus  121  through a non-removable memory interface such as interface  140 , and magnetic disk drive  151  and optical disk drive  155  are typically connected to the system bus  121  by a removable memory interface, such as interface  150 . 
     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  141  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 keyboard  162  and pointing device  161 , commonly referred to as a mouse, trackball or touch pad. 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 a user input interface  160  that is coupled to the system bus, but may be connected by other interface and bus structures, such as a parallel port, game port or a universal serial bus (USB). A monitor  191  or other type of display device is also connected to the system bus  121  via an interface, such as a video interface  190 . In addition to the monitor, computers may also include other peripheral output devices such as speakers  197  and printer  196 , which may be connected through an output peripheral interface  190 . 
     The computer  110  may operate in a networked environment using logical connections to one or more remote computers, such as a remote computer  180 . 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 , although only a memory storage device  181  has been illustrated in  FIG. 1 . The logical connections depicted in  FIG. 1  include a local area network (LAN)  171  and a wide area network (WAN)  173 , but may also include other networks. Such networking environments are commonplace in offices, enterprise-wide computer networks, intranets and the Internet. 
     When used in a LAN networking environment, the computer  110  is connected to the LAN  171  through a network interface or adapter  170 . When used in a WAN networking environment, the computer  110  typically includes a modem  172  or other means for establishing communications over the WAN  173 , such as the Internet. The modem  172 , which may be internal or external, may be connected to the system bus  121  via the user input interface  160 , or other appropriate mechanism. In a networked environment, program modules depicted relative to the computer  110 , or portions thereof, may be stored in the remote memory storage device. By way of example, and not limitation,  FIG. 1  illustrates remote application programs  185  as residing on memory device  181 . It will be appreciated that the network connections shown are exemplary and other means of establishing a communications link between the computers may be used. 
       FIG. 2  may be a high level illustration of a method of detecting and correcting corrupted pages used by an operating system. At a high level as shown in  FIG. 2 , an inpage exception may be noted  200 . One way to note an inpage exception is through a hash mismatch such as when the hash, or signature, of a page is different from the hash that a code integrity module validates against. The code integrity module may store the per-page hashes of critical system components. When the code integrity module detects that a page being loaded no longer matches its expected hash, the code integrity module may return an error code and the memory manager may throw an InPageError exception. This exception may be caught by an error reporting module. 
     When the blocks composing a page on the disk are damaged, an I/O error may be detected by the disk. The disk I/O error may be noted by the disk class driver with a relevant status code such as STATUS_DEVICE_DATA_ERROR, preventing any data from being read. In these cases, the memory manger may throw an InPageError exception with a relevant status code such as STATUS_DEVICE_DATA_ERROR. As with the hash mismatch scenario, this exception may be intercepted by the error reporting module. 
     At block  205 , the page error may be caught by an error reporting module such as the Windows Error Reporting module in Windows. The error reporting module may complete its normal execution based on whether the user has opted in for automatic error reporting. Once the error reporting module catches the exception, it may launch the diagnostic method at block  210 . The error reporting module may be a client and may synchronously request diagnosis from the diagnostic module indirectly through the diagnostic policy service (DPS)  215 . The error reporting module may not be a trace-based “fire &amp; forget” scenario as some displays may be displayed in certain cases  220 . Additionally, in cases where the diagnostic module display is shown, it may need to be coordinated with the error reporting user interface which may run interactively. 
     At block  225 , the local diagnostic policy service may communicate a file recovery request to the inpage error diagnostic module. At block  230 , the method may attempt component recovery by using the system file checking. The system file checking may consult with the system file cache  235  to determine if the file integrity violation is confirmed. The system file checking may also attempt to replace the component with a copy of the corrupt file from the system file cache  240  if the cached copy is available and is non-corrupted. If the faulting page resides on a fixed local drive in the same boot volume as the currently running OS, the diagnostic module may use the APIs provided by the system file checking API (“SFC”) to attempt recovery of the component corresponding to the corrupted binary. If the file and associated component are present in the system file cache and the cached copies are not corrupted, then recovery of the entire component may occur. 
     At block  245 , the inpage error diagnostic module may report the results of recovery attempts  245  to the local diagnostic policy which may then return the results of the recovery attempt to the inpage error client  250 . 
       FIG. 3  may be an illustration of some sample displays that may be created such as the displays  220  in  FIG. 2 . These screens may appear after the error reporting module completes its normal behavior  300 . One of the goals for the method may be to keep the user exchange minimal and to display no user interface, if possible. In order to adhere to this goal, a dialog may only be shown in one case: recovery was successful AND system reboot is required  310 . For this case, the user interface may be required because the user needs to take action in response to the reboot prompt  320 . In all other cases, including those in which the file is actually not corrupted, no user interface may be shown  330 . Additionally, another goal for the interface that may be used when the user interface is shown, the recovery attempt should be tied to the crash that triggered it. This is achieved by making the user interface resemble the error reporting module user interface. 
       FIG. 4  may be an illustration of the user exchange for the method. Note that the event labeled “Invoke INPAGE_ERROR_HANDLER in COFIRE_DM” corresponds to the flowchart in  FIG. 6 , while the decision labeled “Perform LIGHTWEIGHT_CHECK to determine if COFIRE scenario” corresponds to the flowchart in  FIG. 7 . 
     At block  400 , the error reporting module may catch an exception. As noted previously, the exception may be a hash mismatch or a bad disk block. At block  405 , the method may perform a lightweight or local check to determine if the problem noted is a problem the method is designed to address such as a page error. If the problem is not a problem the method is designed to address, the error reporting module may complete its normal behavior and the method may end at block  415 . If the problem is a problem the method is designed to address, the error reporting module may determine what parameters should be collected as part of the error reporting module including the name of the file that caused the paging error  420 . The error reporting method may complete its normal behavior at block  425  and then the error reporting module may start the inpage error handling client  430 . At block  435 , the method may invoke the error handler. 
     At block  440 , the method may determine whether the inpage error handler attempted a recovery. If the inpage error handler does not attempt a recovery, the method may end at block  415 . If the inpage error handler attempted a recovery, at block  445 , the method may determine whether the inpage error handler recovered the file successfully. If the file was not successfully recovered, the method may end at block  415 . If the file was successfully recovered, the method may determine whether a system reboot is required  450 . If a system reboot is not required, the method may end at block  415 . If a system reboot is required, at block the method may display  455  a successful recovery illustration ( 320  in  FIG. 3 ) and the method may end at block  415 . 
       FIG. 5  may be a layered view of the steps leading up to the generation of the types of inpage exceptions handled by the inpage error handler. In general, once the error reporting module catches the exception, it may launch the inpage error handling client, which may synchronously request diagnosis from the inpage error diagnostic module indirectly through the diagnostic policy service (DPS). At block  500 , a page fault may occur. At block  505 , the memory manager  505  may request a page  510 . The code integrity module  515  may pass the request for a page in a file  520  to a file system driver  525 . In another embodiment, the page request  510  may be passed directly to the file system driver  525  without need of the code integrity module  515 . The request for specific disk block  530  may be passed to ClassPNP  535  which may then may an I/O request  540  to the hard disk  545 . 
     The hard disk may send an I/O response  550  or an I/O error  555 . If an I/O response  550  is received by ClassPNP  535 , the blocks of data  560  are communicated to the file system driver  525  which may then communicate the page data to the code integrity module  515 . At block  565 , the code integrity block  515  may perform a hash check on the data receive  570  compared to the page hashes previously calculated. If a hash mismatch is discovered, it is communicated at block  575  and at block  580 , the memory manager  505  generates an exception  585  and reports the exception to the exception reporting module  590 . A hash mismatch occurs when the hash, or signature, of a page is different from the hash that code integrity module validates against. Essentially, the code integrity module stores the per-page hashes of critical system components. When the code integrity module detects that a page being loaded no longer matches its expected hash, code integrity module will return an error code and the Memory Manager will throw an InPageError exception such as STATUS_INVALID_IMAGE_HASH as the status code. This exception will be caught by error reporting module. 
     If at block  550 , an I/O error is sent  555  such as when the blocks composing a page on the disk are damaged, an I/O error may be detected by the disk and the ClassPNP may report an error code  592  to the file system  525 . The error code may then be communicated to  594  to the code integrity module  515  and the error code  596  such as STATUS_DEVICE_DATA_ERROR may be reported to the memory manager  505 . At block  598 , the method may generate an exception which may be reported to the exception reporting module  590 . As with the hash mismatch scenario, this exception will be intercepted by error reporting module. 
       FIG. 6  may be an illustration of the inpage error handling flow.  FIG. 6  may not apply to all inpage errors. It may be used by those inpage errors that pass the lightweight checks in  FIG. 7 . The LIGHTWEIGHT_CHECK logic in  FIG. 7  is executed on the client side in error reporting module, while the expensive HEAVYWEIGHT_CHECK logic in  FIG. 8  is executed only within the inpage error handling diagnostic module. Note that the HEAVYWEIGHT_CHECK logic may include the LIGHTWEIGHT_CHECK logic as well. By running through this series of checks on the client side, the inpage error handling executable does not need to be launched unless it is required. Running these checks on the server side may allow proper handling in the event of spoofed error reporting clients that attempt to trigger the inpage error recovery. 
     At block  610 , the method may perform a heavyweight check to determine if the inpage error module should be invoked to make a call to the system file cache APIs. If the inpage error module is not invoked, an appropriate message is returned such as a RECOVERY_NOT_ATTEMPTED exit code  620  and the method may end at block  630 . If block  610  determines that the heavyweight check should be invoked, at block  640 , the method may call system file cache APIs to replace the component if the file and corresponding component exists in the system file cache. At block  650 , the method may return the system file cache exit code and the method may end at block  630 . 
       FIG. 7  may be an illustration of the lightweight check. At block  700 , the method may determine whether the error is an inpage error. If the determination is no, the method may return false at block  705  and the method may end  710 . If at block  700  the method determines that the error is an inpage error, at block  715 , the method may determine whether the error is an invalid hash error. In another embodiment, code integrity may not be used and this check may not be performed. 
     If the method determines that the error is a hash error, control may pass to block  720 . If the error is not a hash error, control may pass to block  725  where the method may determine whether the error is an I/O error. If the error is not an I/O error, the method may return false at block  705  and the method may end at block  710 . If the error is a I/O error, control may pass to block  720  where the method may determine whether the device hosting file is a fixed, local file. The method may only operate on local drives as remote drives often suffer from communication errors and removable media is unlikely to contain OS system files and may also be read-only (as in the case of CDs or DVDs) so attempting inpage error recovery on this type of storage may not yield much reward. Additionally, fixed local drives may be specifically targeted because these are the drives on which the relevant System File Cache may be kept up-to-date. 
     At block  735 , the method may determine whether the file resides in the same boot volume and operating system directory as the currently running operating system. If the determination is no, the method may return false at block  705  and the method may end at block  710 . This check may be intended to prevent modification of files residing on a partition that belongs to another installed operating system instance with potentially different service. If the determination at block  735  is yes, control may pass to block  740 . 
     At block  740 , the method may determine if the inpage error handling module is disabled through a group policy. If the determination is yes, the method may return false at block  705  and the method may end at block  710 . 
     At block  745 , the method may determine whether the relevant system file cache file is protected. If the determination is false, the method may return false at block  705  and the method may end at block  710 . If the determination is true, the method may return true at block  750  and the method may end at block  710 . 
       FIG. 8  may illustrate a heavier check. At block  800 , if all the lightweight checks pass as described in  FIG. 7 , then the inpage error handler may performs more expensive checks. If the value returned from the lightweight check of  FIG. 7  is false, the method may return false at block  805  and the method may end at block  810 . If the lightweight check of  FIG. 7  returns true, at block  815 , the method may determine whether the inpage error handler invocation rate threshold is exceeded. This throttling is intended to reduce the impact of spoofed error reporting clients designed to trigger the inpage error handler data manager. This spoofing is not excessively difficult because the error reporting module runs in user mode with limited user privilege, so malicious code does not need to run in kernel mode or in a privileged user-mode context for this to occur. Such malicious activity could cause denial of service through excessive inpage error handler disk I/O. Additionally, excessive inpage error handler invocation could also be a sign of imminent disk failure, in which case component recovery should be deferred in order to allow the user to back up critical files and perform drive replacement. 
     If the determination at block  815  is yes, then the method may return false at block  805  and the method may end at block  810 . If the determination at block  815  is no, the method may determine at block  820  whether it encountered the same file recently. If so, it will skip recovery (by returning false at block  805  and the method may end at block  810 ) as the previous attempt was apparently unsuccessful and, hence, there may be no point trying again. If the determination is that the file has not been encountered recently, at block  825 , the method may determine whether another instance of the inpage error handling module is already handling the file or component in question. If the determination is yes, the method may return false at block  805  and the method may end at block  810 . If the determination is no, the method may pass control to block  830 . At block  830 , the method may also invoke the system file cache APIs to determine if there is, indeed, an integrity violation of the supposedly damaged file. If no integrity violation is reported, then recovery is skipped (by returning false at block  805  and the method may end at block  810 ). If the is not an integrity violation, the method may return true at block  835  and the method may end at block  810 . 
     If all the checks pass, the inpage error handler may attempt recovery of the damaged file by invoking the system file checking APIs. Before system file cache attempts to replace the component associated with the file, it will perform an integrity check of the system file cache copy of the component with the expected hashes. If the backup copy is damaged, system file cache recovery will fail, resulting in the failure of the inpage error handler recovery attempt. Additionally, restart information is returned by the system file cache APIs in the success case, which is used by the inpage error handler to determine whether a system reboot is required. 
     The inpage error handler does not “hot-swap” files when the inpage error is encountered; execution fails resulting in a typical user-mode crash. Additionally, it should be noted that the inpage error handler does not handle kernel-mode inpage errors. 
     End-User Scenarios 
     Abby 
     One day, the iexplore.exe file on Abby&#39;s computer suffers from silent data corruption; her hard-disk drive was operating at a slightly higher temperature than recommended, causing magnetic domains in her drive to flip spontaneously. When she launches Internet Explorer, the code integrity module determines that the signature of a page in the iexplore.exe file is inconsistent with the stored hash for that page. Consequently, the code integrity module returns an error code that causes the memory manager to throw an inpage exception. An error reporting module such as Windows Error Reporting (WER) intercepts this exception and sends a report to the error reporting module backend since Abby has opted in for automatic error reporting. The inpage error diagnostic module is able to successfully replace the iexplore.exe file and its related component with the version in the System File Cache. The inpage error diagnostic module alerts Abby that the recovery succeeded and that a system reboot is required, as some of the files replaced were in use at the time of the repair. Abby clicks the “Restart Now” button to restart her computer. The next time Abby starts Internet Explorer, she is able to browse the Web. 
     Ichiro 
     Ichiro has configured his servers to automatically run Disk Defragmenter periodically. One of the hard-disk drives on one of his machines has a bad sector, rendering the Disk Defragmenter executable and other files unreadable. When Disk Defragmenter is supposed to run on this machine, the OS attempts to page in images from the executable, but is unable to do so because the blocks constituting the pages are unreadable. The I/O error causes an inpage exception to be thrown. As Ichiro has the inpage error autorecovery enabled on his servers, the inpage error automatically invokes the system file checking (SFC) APIs to attempt file recovery. Since the file is present in the system file cache, SFC replaces the corrupted file and associated component with a copy from the cache. Although the disk was not defragmented due to the problem encountered, the next time Disk Defragmenter is invoked, the defragmentation completes successfully. Additionally, the error and the action taken are logged to operating system event log. Ichiro later logs into the server and browses the logs in to view the error. 
     Although the forgoing text sets forth a detailed description of numerous different embodiments, it should be understood that the scope of the patent 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 possible embodiment 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. 
     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 claims. Accordingly, it should be understood that the methods and apparatus described herein are illustrative only and are not limiting upon the scope of the claims.