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Topic: Kernel mode

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	Kernel Mode Definition
		Kernel mode, also referred to as system mode, is one of the two distinct modes of operation of the CPU (central processing unit) in Linux.
		When the CPU is in kernel mode, it is assumed to be executing trusted software, and thus it can execute any instructions and reference any memory addresses (i.e., locations in memory).
		This change in mode is termed a mode switch, not to be confused with a context switch (although it sometimes is), which is the switching of the CPU from one process to another.
	www.bellevuelinux.org /kernel_mode.html (781 words)

	Kernel Mode Linux
		Thus, the kernel is protected by CPUs, because programs executed in user mode cannot access memory that belongs to programs executed in kernel mode.
		The kernel code segment is used for the kernel itself, and its privilege level is kernel mode.
		Because the process is executed in kernel mode, the CPU can never switch the memory stack to the kernel stack.
	www.linuxjournal.com /article/6516 (2399 words)

	Kernel Mode Linux: Execute user processes in kernel mode
		Kernel Mode Linux is licensed under the GNU General Public License.
		However, in Kernel Mode Linux, a user program may be executed in kernel mode and the CPU may not switch a stack.
		However, because the kernel patched with Kernel Mode Linux patch is derived from the Linux Kernel, we cannot relax or restrict the conditions made by the original licenser.
	web.yl.is.s.u-tokyo.ac.jp /~tosh/kml (1950 words)

	NT Drivers - FAQ - Basics
		GDI drivers, also known as Win32 Graphics Drivers and Kernel Mode Graphics Drivers, run in kernel mode but are nonetheless very different from the "kernel mode drivers" that are the main focus of this FAQ.
		In general, kernel mode drivers are the only drivers that can touch I/O hardware, although GDI video drivers do have access to the video card.
		By contrast, kernel mode drivers usually implement functions that require waiting for an interrupt, waiting for a device to become available, etc. During such "waiting" periods the kernel mode driver simply returns to its caller, allowing the caller to perform other work in parallel with the I/O operation.
	www.cmkrnl.com /faq01.html (1755 words)

	Ring (computer security) - Wikipedia, the free encyclopedia
		In a monolithic kernel, the kernel runs in supervisor mode and the applications run in user mode.
		If a processor generates a fault or exception condition in a user mode, in most cases system stability is unaffected; if a processor generates a fault or exception condition in kernel mode, most operating systems will halt the system with an unrecoverable error.
		Thus, a fault in ring0 (the kernel mode with the highest privilege) will crash the entire system, but a fault in ring 2 will only affect rings 3 and beyond and ring 2 itself, at most.
	en.wikipedia.org /wiki/Kernel_mode (1629 words)

	BSQUARE Corporation Windows Embedded Blog
		A kernel mode thread may have additional subtle capabilities that are cpu specific because it runs at a higher cpu privilege level.
		Kernel mode threads also had the ability to access hardware through statically mapped kernel mode addresses; after all, they had the same privileges as the kernel.
		Performance is already fast because there is a single thunk from user to kernel mode, and the remaining transitions between the kernel, filesys, gwes and device in a particular function call are already in kernel mode.
	www.bsquare.com /blog/default-sep_18.asp (1061 words)

	Linux Kernel Documentation :: ia64 : fsys.txt
		To recap, the normal states of execution are: 15 16 - kernel mode: 17 Both the register stack and the memory stack have been 18 switched over to kernel memory.
		The user-level 29 state remains in the CPU registers and some kernel state may 30 be stored in bank 0 of registers r16-r31.
		A srlz.d instruction is used 185 to ensure the CPU is in little-endian mode before the first 186 load/store instruction is executed.
	www.mjmwired.net /kernel/Documentation/ia64/fsys.txt (1500 words)

	Writing AIX kernel extensions
		Kernel extensions are routines added to the kernel to extend its functions.
		Kernel extensions are an important part of the AIX kernel architecture, and they are similar to dynamically loadable modules available on other platforms, such as Linux®, that add function to the running kernel without the need of a machine reboot.
		Dual-mode kernel extensions can be used to simplify the loading of kernel extensions that run on both the 32- and 64-bit kernels.
	www.ibm.com /developerworks/aix/library/au-kernelext.html?ca=drs- (2540 words)

	Linux: Kernel Graphics Subsystem \| KernelTrap
		With kernel modesetting support, the kernel should be able to display panic and oops messages directly on the console, even if a graphical application is running, since it would have awareness of the current mode, display depth, pitch, and other variables needed to display output.
		Of course, the kernel can't unconditionally preempt the graphics device to set a new mode, but having modesetting in the kernel will give it a much better chance of coordinating with the DRM command dispatch code to find a good time to set a new mode.
		This is a good reason to move the VT drivers from the kernel to userspace, not to move more userspace into the kernel.
	kerneltrap.org /node/8242 (2861 words)

	Kernel Korner - Kernel Mode Linux for AMD64
		Kernel Mode Linux (KML) is a technology that enables the execution of user processes in kernel mode.
		The CPU then raises its privilege level from user mode to kernel mode and jumps to the target address of SYSCALL, which is specified by the kernel in advance.
		To execute user processes in kernel mode, the only thing KML does is launch user processes with the CS segment register, which points to the kernel code segment instead of user code segment.
	www.linuxjournal.com /article/8023 (2665 words)

	[No title]
		The purpose of nt is to implement the heart of the kernel itself and to provide the core library interface to device drivers.
		If the kernel were to crash, any code that the payload had intended to execute may not actually get a chance to run depending on how the payload is structured.
		The purpose of IRQLs are to allow the kernel to mask off interrupts that occur at a lower level than the one that the processor is currently executing at.
	www.uninformed.org /?v=3&a=4&t=txt (8804 words)

	IIS: Using Kernel-Mode SSL in Windows 2003 Server SP1
		Kernel Mode SSL is enabled by setting a registry key, however the current implementation does have some drawbacks, so careful evaluation is required before enabling this functionality.
		So, the response is passed down into kernel mode, then back into user mode (to LSASS where the response is encrypted), and then back into kernel mode (http.sys) to be sent back to the client.
		However, using kernel mode SSL does have a number of drawbacks, in that certain features are not available.
	www.adopenstatic.com /faq/IISKernelSSL.aspx (402 words)

	C++ for Kernel Mode Drivers: Pros and Cons
		Versions of standard libraries provided with the build environment for use in kernel mode are not necessarily the same as those provided in user mode, because they cannot rely on the Win32® API and because they must be written to conform to kernel mode requirements.
		Not all library functions are available in kernel mode, particularly those associated with the “advanced” C++ language features.
		Whether this lack of demand is a consequence of the other problems masking it or because it is not useful in kernel mode is unknown.
	www.microsoft.com /whdc/driver/kernel/KMcode.mspx (3682 words)

	Nynaeve » Blog Archive » A catalog of NTDLL kernel mode to user mode callbacks, part 5: ...
		The kernel mode dispatcher for user mode calls will attempt to convert the thread to a large kernel stack when a call is made, as the typical sized kernel stack is not large enough to support the number of recursive kernel mode to user mode calls present in a many complicated window messaging calls.
		Furthermore, the kernel mode to user mode call interface is really not as convenient as you might imagine for things like asynchronous notifications to user mode clients.
		At that point, if you are going to have to be blocked on kernel mode, you might as well just use the recommended mechanisms for communication, such as a pended IRP (these mechanisms also integrate much better into a high performance work item based architecture).
	www.nynaeve.net /?p=204 (1367 words)

	Kernel-Mode Capabilities
		For example, a kernel module that is a device driver may need to support a large number of disks and controllers.
		Kernel modules can save timestamps that can be passed to applications on request for many purposes.
		Kernel threads allow kernel modules to perform other useful work while waiting for a device to produce its next event, such as the completion of a disk transfer or the receipt of a packet from the network.
	www.helsinki.fi /atk/unix/dec_manuals/DOC_51/HTML/ARHYGBTE/KRMKRNCP.HTM (4696 words)

	Linux Kernel Overview
		The Linux kernel is said to be monolithic; a single large executable, consisting of several logically divided components.
		The kernel is reentrant; several processes may be executing in kernel mode at one time.
		One process may only replace another in kernel mode if it has voluntarily relinquished the CPU, leaving data structures in a consistent state, hence the kernel is termed "non-preemptive".
	www.kernelhacking.org /docs/kernelhacking-HOWTO/indexs03.html (2104 words)

	Nynaeve » Blog Archive » A catalog of NTDLL kernel mode to user mode callbacks, part 1: Overview
		As I previously mentioned, NTDLL maintains a set of special entrypoints that are used by the kernel to invoke certain functionality on the behalf of user mode.
		The mechanism that the kernel uses to invoke these entrypoints is to alter the context that will be realized upon return from kernel mode to user mode.
		The return to user mode context information (a KTRAP_FRAME) is modified such that when kernel mode returns, instead of returning to the point upon which user mode invoked a kernel mode transition, control is transferred to one of the three dispatcher routines.
	www.nynaeve.net /?p=200 (1041 words)

	Installing User Mode Linux
		There are several mirrors that have the kernel source code available for download.
		If you download a version of the kernel that is earlier than 2.6.9 you will also need to download a seperate patch for the uml architecture.
		There are many different kernel options that you will need to select in order to build a fully functional kernel.
	www.clarkson.edu /class/cs644/kernel/setup/uml/uml.html (1172 words)

	Agnitum BLOG: Kernel mode hooks or user mode hooks – what’s best for the firewall
		In his test result analyses, Matousek claims that Agnitum uses user mode hooks instead of kernel mode hooks, and is therefore cheating.
		Matousek omits to mention is that kernel mode hooks can also be bypassed, so this approach cannot provide 100% protection either.
		We don’t agree that the “kernel mode hooks” approach is better than the “user mode hooks” approach; it is our belief that a blend of the two techniques is the most effective way to deliver robust firewall protection.
	agnitumblog.blogspot.com /2006/12/kernel-mode-hooks-or-user-mode-hooks.html (504 words)

	Kernel Mode Linux: Execute user processes in kernel mode
		Kernel Mode Linux is licensed under the GNU General Public License.
		However, in Kernel Mode Linux, a user program may be executed in kernel mode and the CPU may not switch a stack.
		However, because the kernel patched with Kernel Mode Linux patch is derived from the Linux Kernel, we cannot relax or restrict the conditions made by the original licenser.
	www.yl.is.s.u-tokyo.ac.jp /~tosh/kml (1952 words)

	Symantec Security Response Weblog: Assessment of Vista Kernel Mode Security
		The Windows Vista operating system launches one of the most aggressive assaults on kernel mode security threats seen to date; even when compared to those capabilities seen in Mac OS X, Linux, and many UNIX variants.
		Our new paper, Windows Vista Kernel Mode Security takes a detailed look at the Vista boot process and these new security technologies.
		Kernel mode threats such as Rootkits and malicious drivers have become commonplace and eradicating this risk is certainly in everyone’s best interest.
	www.symantec.com /enterprise/security_response/weblog/2006/08/assessment_of_vista_kernel_mod.html (656 words)

	system calls in Kernel Mode ??? \| KernelTrap
		Kernel has it's own facilities and trying to put any user space code there is generally not a good idea.
		I am not able to understand that open() etc are system calls and how are we able to make these calls inside the kernel mode.
		Strictly speaking this is not a system call, because it omites trap to enter the kernel mode, system call number and so.
	kerneltrap.org /node/6120 (360 words)

	Inside the Blue Screen
		Kernel mode is a highly privileged processor mode, with direct access to all hardware and memory; user mode is a less privileged mode, with no direct access to hardware and restricted access to memory.
		User mode is the mode in which applications and operating system environment subsystems execute.
		NT implements the transition between user mode and kernel mode as a system call gateway, through which the passage of data is precisely controlled.
	www.windowsitpro.com /Articles/Index.cfm?IssueID=26&ArticleID=301 (1562 words)

	freshmeat.net: Project details for Kernel Mode Linux
		Kernel Mode Linux is a technology which enables the execution of user programs in a kernel mode.
		Unlike kernel modules, user programs are executed as ordinary processes (except for their privilege level), so scheduling and paging are performed as usual.
		Although it seems dangerous, the safety of the kernel can be ensured through such methods as static type checking, software fault isolation, and so forth.
	freshmeat.net /projects/kml (174 words)

	David Wang : HOWTO: Use the HTTP.SYS Kernel Mode Response Cache with IIS 6
		When you do a search against "HTTP.SYS Kernel Response Cache IIS 6", you will inevitably find a large body of literature repeatedly talking about how the kernel mode response cache effectively improves performance and lightens server load by removing the kernel/user mode transitions, improves request/response latency, improves...
		This lack of consolidated information, along with several newsgroup questions about how the kernel mode response cache works, is what motivated me to write this entry about the background and the raw mechanics of how to leverage this cache from IIS 6.0.
		I assumed since the kernel cache caches heavily accessed files, such as my blog's RSS feed, that the kernel was keeping the file in memory and thus serving it from the kernel instead of the hard disk.
	blogs.msdn.com /david.wang/archive/2005/07/07/HOWTO_Use_Kernel_Response_Cache_with_IIS_6.aspx (3424 words)

	Converting Win32 Kernel-mode Print Drivers to User Mode
		The UI component always runs in user mode — usually in the context of the process of the user requesting the printing — but the rendering part has been quite schizophrenic over the last ten years, moving back and forth between user mode and kernel mode.
		Kernel mode drivers have been more and more discouraged with each subsequent OS release: Windows 2000 Logo compliance requires user mode drivers (though an exception was made early in the program for proven reliable kernel mode drivers), and Windows 2003 does not allow them by default, requiring a Group Policy change to enable.
		We're not sure how much support for C++ exists for kernel mode drivers, but we can't help but believe that many of these driver authors limited themselves to C only as a defensive measure.
	www.unixwiz.net /techtips/win32-pdriver-ktou.html (4718 words)

	WD-3: DLLs in Kernel Mode
		Kernel driver writers are often not aware that they can use exactly the same concept in kernel mode.
		In terms of the C source code, a kernel DLL is virtually identical to a user-mode DLL.
		Your kernel DLL will be automatically loaded as soon as any other driver makes a reference to it, and is automatically unloaded when the last referring driver unloads.
	www.wd-3.com /archive/KernelDlls.htm (2104 words)

	NT Architecture basics
		Kernel mode is a highly privileged processor mode, with direct access to all hardware and memory; user mode is a less privileged mode, with no direct access to hardware and restricted access to memory.
		User mode is the mode in which applications and operating system environment subsystems execute.
		NT implements the transition between user mode and kernel mode as a system call gateway, through which the passage of data is precisely controlled.
	www.geocities.com /nafiton/NTarchit.html (1633 words)

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