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Row hammer

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Last Updated: 18 January 2022

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General | Latest Info

Past Few Days Have Been Busy If Youre Trying To Keep Up With Pace Of Computer Security News. Between serious Chromium bug that is actively being exploited on Windows 7 systems, NSA releasing one of their tools as open source Project, and new Spectre - like speculative execution flaw in Intel processors, there is lot to digest. Continue reading Spoiler, Use - After - Free, and Ghidra: this Week in Computer Security over on Cloudflare blog, find himself wondering about Computer Memory, as we sometimes do. Specifically, he pondered if he could detect refresh of his SDRAM from within running program. Were probably not ruining surprise by telling you that answer is yes with little more than 100 lines of C and help from our old friend Fast Fourier Transform, was able to detect SDRAM refresh cycles every 7818. 6 ns, lining right up with expected result. D in SDRAM stands for dynamic, meaning that periodically refreshed by reading and writing, data in memory will decay. In this kind of memory, each bit is stored as charge on tiny capacitor. Give enough time, this charge can leak away to silicon, turning all 1s to 0s, and destroying data. To combat this process, memory controller periodically issues refresh command which reads data before it decay, writes data back to fully charge capacitors again. Do it often this will preserve memory contents indefinitely. Sdram is relatively inexpensive and available in large capacity compared to alternatives, but drawback is that CPU ca access portion of memory being refresh, so execution Get delayed whenever memory access and refresh cycles collide. At 33 annual Chaos Communications Congress, and presented not one, not two, but three great hacks that were all based on exploiting memory de duplication in virtual machines. If youre interested in Security, you should definitely watch talk, embed below. And grab slides too. Memory de - duplication is forbidden fruit for large VM setups, obviously dangerous but so tempting. Imagine that youre hosting VMs and you notice that many of machines have same things in memory at same time. Maybe we were all watching same cat videos. They can save global memory across machines by simply storing one copy of cat video and pointing to shared memory block from each of machines that use it. Notionally, separate machines share memory. What could go wrong? Project Zero, Google Security analyst unit, has proven that Rowhammer can be used as exploit to gain superuser privileges on some computers. Row Hammer, or Rowhammer is method of Flipping Bits in DRAM by hammering rows with Fast read accesses. And rest of Project Zero team learn of Rowhammer by reading 2014 paper Flipping Bits in Memory Without Accessing Them: Experimental Study of DRAM Disturbance Errors.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

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* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

Overview

Current DRAM in modules called DIMMs. If you buy modern memory module for your PC, you are buying DIMM. If you look at DIMMs, most DIMMs have chips on both sides. Each side of is rank. Each rank again consists of number of banks. Banks are in physical chips you can see. Inside bank, you find two dimensional matrix of memory cells. There are 32k in matrix and 16k or 512k cells per row. Each cell stores one bit and consists of transistor for control and capacitor which stores charge to signify bit is equal to 1 and no charge when bit is equal to 0. Thus, Row stores 8kb or 64kb of data depending on exact kind of DRAM you have in front of you. When you read or write from / to DRAM, entire row is first into so - call so - called Row buffer. This is because reading discharges capacitor and since writes rarely rewrite entire row. Reading Row into Row is called activating Row. Active Row thus Cache in Row buffer. If Row is already active, is not reactivate on requests. Also, to prevent capacitors loose charge overtime, are refreshed regularly by activating rows. This section is based on et Al. Where not otherwise note. When Row activated, small effect is caused on neighboring Row due to so - called Cross talk effects. Effect can be caused by electromagnetic interference, so call conductive where there is minor electric conductivity in DRAM modules where it shouldnt be. And finally, so - called hot - carrier - injection may play role where electron reaches sufficient kinetic energy where it leaks from system or even permanently damages parts of circuitry. Net Effect Is Loss Of Charge In DRAM Cell Which If Large Enough Will Cause Bit To Flip. Consequently, it is possible to cause Bits to flip in DRAM by reading or writing repeatedly and systematically from / to two rows in DRAM to Bit Flips can introduced in Row up to 9 rows away from these two aggressor rows. 9 rows called victim rows. Most errors happen in row immediately next to aggressive row. Picking aggressor so they bracket victim row is called double side row hammering and is far more efficient than normal row hammering. Using two rows to hammer surrounding rows is called amplified single side hammering and can be useful in exploitation scenarios. If victim rows are refreshed before enough Cross talk can be generated, no Bit is incur. As rule of thumb, higher frequency of activation, higher probability of Flipping Bits. It has been shown that bits can be in less than 9 milliseconds and typically require around 128k Row activations.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

Implications

Data Theft Technique Called Rowhammer Has Fascinated And Worried Cybersecurity Community For Years Now, Because It Combines Digital And Physical Hacking In Ways That Are Both Fascinating And Unaccounted For. Since its discovery, researchers have steadily refined attack, and expanded array of targets it works against. Now, researchers have significantly increased scope of potential threat to include critical devices like servers and routerseven when they have components that are specifically thought to be immune. Rowhammer Attacks are fiendishly technical. They involve strategically executing program over over on row of transistors in computer's memory chip. Idea Is To Hammer That Row, Until It Leaks Some Electricity Into Adjacent Row. That leakage can cause bit in target row to flip from one position to another, slightly altering data store in memory. Skilled Rowhammer can then start to exploit these tiny data changes to gain more system access. See? It's pretty bonkers. Previously, Rowhammer was understood to have typical random access memory used in many off - shelf computers. Rowhammer has also been shown to threaten in Android phones. But on Wednesday, researchers in VUSec research Group at Vrije Universiteit in Amsterdam published details of next - generation Rowhammer ambush that can target what's known as error - correcting code memory. Ecc memory was previously thought to Rowhammer's data manipulations, because it has redundancies and self - correcting mechanisms that deal with data corruption. Ecc memory is used in systems that need exceptional reliability and can't inaccuracies, like financial platforms. Researchers note that ECC memory really do defeat past versions of Rowhammer Attacks, in studying ECC implementations they find that they could finesse and establish Rowhammer methods to work against ECC as well. As with all Rowhammer work, ECC is difficult to defend against without literally redesigning and replacing memory chips. Ecc is not really completely break; it still Get you reliability, says Lucian Cojocar, one of Vrije researchers who participated in work. Even our reported several possible software defenses. But we 've found that normal Rowhammer is reproducible for ECC. Its not that straightforward how to mitigate it. Difficulty In Hacking ECC Is Finding Way Around Memory's Build - In Defenses. First Step Of Any Rowhammer Attack Is Reconnaissance Phase Called Templating, During Which Attacker Quietly Probes To Identify Which Bits Will Be Flippable Before Regrouping To Actually Initiate Changes. Ecc memory makes templating harder, because if attacker flips one bit, system will automatically change it back, making it difficult to detect vulnerable bit's location. And if attacker instead flips two bits, memory will crash program. But VUSec researchers find that they flip three bits simultaneously, ECC won't spot change. Challenge Then Becomes To Track Which Bits Are Flippable, When ECC Memory Corrects Them So Quickly.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

Sources

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions.

* Please keep in mind that all text is machine-generated, we do not bear any responsibility, and you should always get advice from professionals before taking any actions

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