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Topic: NX Bit

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	NX bit (via CobWeb/3.1 planetlab2.cs.unc.edu) (Site not responding. Last check: 2007-10-13)
		NX stands for "no execute", a technology used in CPUs such as Sun's Sparc, Transmeta's Efficeon, and newer 64-bit x86 processors to prevent code from being executed on areas of memory flagged with an NX bit.
		An operating system with the ability to emulate and/or take advantage of an NX bit may prevent the stack and heap from being executable, and may prevent executable memory from being writable.
		Linus Torvalds has taken an interest in the NX patch, and believes it may be wise to have NX enabled by default; thus, it will be merged with 2.6.8.
	publicliterature.org.cob-web.org:8888 /en/wikipedia/n/nx/nx_bit.html (1760 words)

	Security Ahoy! Flying the NX Flag on Windows and AMD64 To Stop Attacks
		NX, which stands for "No Execute Bit," is a one-bit flag that goes with each entry in the memory address table.
		The NX data/executable check is similar to other run-time testing the processor does to ensure that non-privileged (user) code can't access privileged (supervisor) code and data, and to prevent writes into read-only address spaces.
		NX support is also going to be a part of Windows Server 2003 Service Pack 1 (you can download the second release candidate), and the forthcoming 64-bit versions of Windows XP and Windows Server 2003.
	www.devx.com /amd/Article/27809 (1178 words)

	NX and XD, No Execute and Execute Disabled
		NX or No eXecute (the abbreviation doesn't make sense to us either) is a hardware solution to buffer overflows.
		The NX bit refers to bit 63 out of 64 which is the last bit (yeah, the counting starts at "0") in the paging table entry of the x86 series of processors.
		This bit can be set to a "0" to allow code execution or a "1" to signify data storage.
	www.bestpricecomputers.ltd.uk /guides/NX-XD.htm (889 words)

	NX fever seizes Intel, Transmeta, VIA, guy in local pub (Site not responding. Last check: 2007-10-13)
		First implemented in common consumer hardware by AMD (but of course it's been around for ages), the NX bit is designed to help the CPU decide whether or not to execute code.
		While technically this could apply to just about anything executable, designers have maintained that the NX bit is intended to stop malicious buffer overruns such as those found in worms and viruses such as Sasser and MSBlast.
		If a malicious bit of code sneaks in, it won't be executed by the CPU if the NX bit has already been properly set.
	arstechnica.com /news/posts/1084986792.html (637 words)

	A Brief Look At NoMachine NX
		NX also implements extra cleverness for handling large images on low bandwidth connections - large images may be split up into smaller chunks and streamed with other X messages interleaved with the chunks, thereby allowing the connection to be efficiently shared between mutliple clients.
		NX Proxy: this is the bit which does the actual compression and de-compression.
		NX Agent: the term agent is used to describe a component to which the screen is rendered before being proxied across the network to the actual X server.
	www.gnome.org /~markmc/a-look-at-nomachine-nx.html (1594 words)

	OSNews.com (Site not responding. Last check: 2007-10-13)
		Too bad that the Intel chips will not be competitively priced with their pure 32 bit ones, and to top it off, these x86-64 clones still have no NX bit.
		The NX bit has been incorporated into the new E0 stepping, and will be available around Sept 24th, though only in LGA775 socket based Prescott P4s.
		NX bit is not a major concern at all at the moment, for most needs.
	www.osnews.com /comment.php?news_id=7911 (1406 words)

	NX bit - t-break and Middle East Gamers Forums
		Interestingly, Transmeta's NX support is actually not hardware, since the CPU is already emulating x86, they only have to change their code-morphing to emulate x86 with the NX bit.
		NX bit has been around for quite some time, it is the inside almost every RISC machines out there, including AMD's K8.
		With NX bit feature enabled, Code will stopped at end of cClassName subroutines, and when (because altered by virus) code is still not terminated, the processor will read through NX marked area, and produced an error instead executing it.
	www.tbreak.com /forums/showthread.php?t=23124 (3560 words)

	[No title]
		"NX (No-Execute) bit: Initial implementation will not support the NX bit." -- http://www.ussg.iu.edu/hypermail/linux/kernel/0402.3/0276.html "Even though there are some differences between Intel’s and AMD’s 64-bit extended processors’ capabilities, such as NX (non execute) bit featured in AMD64" -- http://www.xbitlabs.com/news/cpu/display/20040325151223.html "Both Intel and Advanced Micro Devices (AMD) have defined and shipped Windows-compatible architectures for execution protection.
		If you look at the cpuid feature-bit description in the IA32e pdf, it says function 80000001-edx bits 28-21 are reserved, and bits 19-12 are reserved, with no mention at all of bit 20 (the NX feature bit).
		http://www.xbitlabs.com/news/cpu/display/20040310223922.html NX (non execute) bit featured in AMD64 http://www.xbitlabs.com/news/cpu/display/20040225144527.html Analyst: Intel Reverse-Engineered AMD64 April 5, 2004 By Mark Hachman http://www.extremetech.com/article2/0,1558,1562294,00.asp "The core of AMD’s Enhanced Virus Protection is the so-called NX bit in the page-translation tables that specifies whether instructions can be executed from the page.
	users.utu.fi /juhehe/jutut/NX-bit.txt (783 words)

	Protect Your Vista App with AMD Enhanced Virus Protection
		NX only protects against jumping to code in a data page; it doesn't keep a stack overwrite from sending a program off to a Windows function inside a system DLL that might further the attacker's aims.
		For NX to be applied to a given executable, three conditions must be met.
		And finally, Vista has to mark all of the program's non-code pages with the NX flag, which is determined by the operating environment (32-bit or 64-bit Vista), boot configuration options, and the program itself.
	www.devx.com /amd/Article/31740 (1347 words)

	HardwareCentral - CPU-Based Security: The NX Bit.
		Basically, NX uses processor hardware to discourage the kind of virus, worm, and Trojan Horse attacks seen in scourges such as Blaster, Sasser, and Code Red, which have cost companies billions of dollars in downtime and disinfectant chores.
		Intel is expected to add NX (or XD) to the next generation of its 90-nanometer-process Pentium 4 "Prescott" CPUs -- bundling the security enhancement with a larger 2MB Level 2 cache and perhaps a faster 1066MHz front-side bus -- in the fourth quarter of this year.
		And VIA Technologies promises that NX support will be part of its forthcoming C5J "Esther" core, the IBM-manufactured, 90-nanometer, silicon-on-insulator successor to today's power-thrifty C3 processor; the C5J is planned to offer clock speeds up to 2GHz with a front-side bus up to 800MHz, but no ship date has been announced yet.
	www.hardwarecentral.com /hardwarecentral/reports/article.php/3358421 (1005 words)

	Dr. Dobb's \| XP Service Pack 2 Release Candidate 1, Or "That's Why They Call it a Beta" \| June 2, 2004 (Site not responding. Last check: 2007-10-13)
		NX is supported by the 64-bit AMD architecture while running in 32-bit mode, and presumably will be in Intel's upcoming Nocona AMD-compatible chips.
		The NX bit will be enabled for desktops, but the 64-bit extensions won't.
		NX lessens the chances that some malware exploits will work; for instance, that a buffer overflow could write somewhere it should not.
	www.ddj.com /184406490 (2500 words)

	Red Hat Now at 'NX' Level
		NX security is a significant addition for Red Hat, in that it effectively closes the door on a common virus security exploit.
		The NX "bit" prevents a virus or worm from executing its malicious payload.
		NX security has also been referred by vendors such as AMD as "Enhanced Virus Protection" because of its ability to stop viruses in their tracks.
	www.internetnews.com /dev-news/article.php/3404731 (718 words)

	LWN: x86 NX support
		AMD added a no-execute (NX) permission bit to the page table entries in its 64-bit processors; Intel has recently said it will be supporting this mode as well.
		To that end, Ingo Molnar has posted a patch bringing NX support to the x86 architecture; his patch is based on previous work done by Intel and the x86_64 NX support by Andi Kleen.
		It also applies the NX bit to the kernel itself; kernel text is marked executable, but kernel data is not.
	lwn.net /Articles/87814 (762 words)

	AMD64 Linux kernel and the NX bit LG #107
		This is what the AMD64 NX bit which is supported by the Linux kernel attempts to achieve.
		The results of running the previous program on a 32 bit Athlon system with the executable marked first as requiring an executable stack and then as not requiring an executable stack were identical - in both cases, the program worked as expected, executing the array and thereby writing to the parallel port.
		It seems that having the NX bit on for all programs is a good thing.
	linuxgazette.net /107/pramode.html (2028 words)

	J!NX Forums - bit torrent
		Posted - 08/11/2004 : 9:20:55 PM Yeah it depend's on who uploaded the file and what bit torrent file server you are using, I think.
		And it could maybe depend on what bit torrent client you are using also, I don't know though.I don't have a clue how it work's but I think it's like p2p.
		Posted - 08/12/2004 : 02:15:42 AM bit torrent is gay O_O Download the torrents and use Overnet/eDonkey to get them...
	www.jinx.com /forum/topic.asp?TOPIC_ID=10902 (296 words)

	[No title]
		The prefix for the pair * (which is one bit shorter) is allocated to one of the pair; then, * skipping the BITS entry for that prefix length, a code word from the next * shortest nonzero BITS entry is converted into a prefix for two code words * one bit longer.
		An attempt has been made to use 16 bit or 8 bit quantities (except for an accumulator) to make the relationship with an IP code more likely.
		The Huffman code can be up to 16 bits long and temp2 can be up to 15 bits for a total of 31 bits.
	sohowww.nascom.nasa.gov /solarsoft/packages/ana/sources/trace_jpeg.c (1412 words)

	LostCircuits, CPU Guide (Site not responding. Last check: 2007-10-13)
		The NX bit is a whole different story: the CPU already has mechanisms to check whether it can access a particular page of memory at any given time anyway.
		That means the NX, or, in Intel parlance, DX bit (or maybe XD, depending on who’s talking about it, but either way, standing for some variant of Deny eXecution) is really quite simple to implement.
		All AMD 64-bit processors have supported the bit from the beginning, likewise, the correct support was incorporated into the 64-bit version of Windows (in beta for over 2 years and counting) from the first beta versions on.
	www.lostcircuits.com /cpu/amd_a64-4000/12.shtml (699 words)

	UGS: About Us: Newsroom: Press Release
		Testing has demonstrated that some NX functions will run up to 50 percent faster in a multi-core environment, offering significant benefits for many complex applications found in the automotive, aerospace and consumer products industries.
		UGS’ support for Windows XP Professional x64 Edition will be available with the next release of NX scheduled to begin shipping in the fourth quarter of this year.
		Headquartered in Plano, Texas, UGS’ vision is to enable a world where organizations and their partners collaborate through global innovation networks to deliver world-class products and services while leveraging UGS’ open enterprise solutions, fulfilling the mission of enabling them to transform their process of innovation.
	www.ugs.com /about_us/press/press.shtml?id=4084 (811 words)

	AMD64
		While not technically required for 64-bit computing, the NX Bit is a processor feature that provides for a more tightly controlled software environment.
		It should be noted that the NX bit has long been available on 32-bit x86 processors in the PAE (Paged Addressing Environment) mode, originally introduced in the 80286 processor.
		The intended primary mode of operation of the architecture; it is a combination of the processor's native 64 bit mode and a 32 bit compatibility mode.
	www.mrsci.com /Microprocessors/AMD64.php (1591 words)

	Audigy 2 NX bit-perfect SPDIF - Hydrogenaudio Forums
		I have an audigy 2 platinum, no bit-perfect output is possible and the NX uses the same chip I think.
		Audigy 2 NX USB use different chip from PCI based Audigy solution, it is possible that it support bit-perfect output.
		A proper test would be digitally recording the digital output and compare bit by bit with the original.
	www.hydrogenaudio.org /forums/index.php?showtopic=45809 (827 words)

	NX bit - Wikipedia, the free encyclopedia (via CobWeb/3.1 planetlab2.cs.unc.edu) (Site not responding. Last check: 2007-10-13)
		Any section of memory designated with the NX attribute means that it's only to be used for storing data, so that processor instructions should not reside there, and cannot be executed if they do.
		"Software DEP" is unrelated to the NX bit, and is what Microsoft calls their enforcement of Safe Structured Exception Handling.
		When NX is supported, it is enabled by default.
	en.wikipedia.org.cob-web.org:8888 /wiki/NX_bit (3057 words)

	Linux: x86 No Execute Support (Site not responding. Last check: 2007-10-13)
		Originally introduced by AMD with their Athlon 64 and Opteron processors and marketed as Enhanced Virus Protection, Ingo notes that support for this new bit was also announced by Intel, Transmeta and VIA.
		This NX thing is a newcomer, and it is long overdue at that.
		This new NX bit is basically what a lot of other systems have had for years.
	kerneltrap.org /node/view/3240 (2719 words)

	EM64T For 64bit CPU - The PC Guide Discussion Forums
		The NX bit was an AMD innovation built into their K8 core in anticipation of Microsoft's next-gen OS, known as "Longhorn".
		AMD's current implementation of the NX bit isn't enabled on all the K8-based CPU's, and Intel tried to copy AMD's plans for NX just by looking at their whitepapers and got it wrong, so NX capabilities will have to wait until those two get things straightened out.
		Expect future NX bit support via the OS to be much like HT support is handled now, which is to say that it will most likely be auto-detected.
	www.pcguide.com /vb/showthread.php?t=33856 (829 words)

	AnandTech: A bit about the NX bit; Virus Protection Woes
		NX protection seems great; it stops viruses dead in their tracks and eliminates those pesky buffer overflows we have been hearing so much about for the last 15 years.
		In fact it seems that NX provides several layers of false security, particularly since it only stops some buffer overflows and whether or not it stops any viruses has yet to be seen yet.
		To really explore how NX benefits us, and where it provides a false sense of security, we must understand one of the scenarios that it supposedly prevents against.
	www.anandtech.com /cpuchipsets/showdoc.aspx?i=2239 (741 words)

	09.24.98 Oki nX 65K: EDN's 25th Annual Microprocessor/Microcontroller Directory
		Oki also sells an nX 66K series, an extension of the 65K core with a 16-bit core and an 8-bit bus.
		One set acts as the current set for processing; switching to a new set makes for a fast context switch because no registers have to be saved.
		Special instructions: The nX 65K's bit-manipulation instructions are set, clear, transfer to carry, jump on bit set, and jump on bit clear.
	www.edn.com /archives/1998/092498/8_nX65K.htm (425 words)

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