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Validation, Test and Performance Characterization of DDR Memory Subsystems

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We here at FuturePlus often use the Google StressApp memory test to exercise the DDR Memory.  One recent discovery was the nice Gaussian distribution we saw when measuring the number of simultaneous open banks.  The graph below shows how many Banks are open at one time as a percent of total cycles.  An important metric.  Open banks speed up performance but at the cost of power consumption.  

Open_banks_stress_app.png

Figure:  DDR Detective NUMBER OF SIMULTANEOUS OPEN BANKS

What can we learn from this type of analysis? 

Characterizing workloads can lead to better software, compilers and BIOS settings for the memory controller.  Also in the area of CyberSecurity certain critical workloads may have unique signatures.  If a virus is present the signature might be disturbed.

The DDR Detective is now a Finalist in the 2015 DesignCon BEST IN TEST!            2015_BestinDesignTest_Finalist_Green.png

Rowhammer.js: Row Hammer Attacks Can Now Be Triggered Through Webpages

 

(July 31st, 2015)  The unique and terrifying computer attacks known as 'Row hammer' can now be triggered through a webpage. In a paper by security researchers Daniel Gruss, Clémentine Maurice and Stefan Mangard reveal how what once used to be perceived as an attack dependent on the instruction of the CPU can now be triggered simply through use of a web browser.

This attack on the physical memory of a system is so destructive because it can occur to any operating system and can potentially gain access to data stored. Row hammer events do not affect the address bits being accessed but those in adjacent rows due to the accessed row being hammered with a charge over and over and ultimately leads to data corruption. Before it was believed to only occur through local execution on the computer, but now, it’s been found that it can occur at a remote location through Javascript, which is the scripting language for nearly 90% of webpages now. These three researchers developed a piece of code that escape’s the security sandbox of a browser and can perform a Row hammer event on a system’s hardware.

The best solution to the problem so far is shutting off Javascript on unreliable sites; browsers are unable to patch this problem since there is nothing that can be patched. Fortunately, Rowhammer events are very hard to control and their code is very difficult to replicate, but it does raise huge security concerns about the memory of a system. Google’s own security researchers showed how row hammer events can lead to gaining access of the entire memory of a computer, but this was done locally on the computer and was not tested by the researchers of Rowhammer.js. 

FuturePlus remains at the forefront of this topic and has introduced test equipment that can monitor the DDR3 memory bus in a server, laptop or embedded design to identify Row hammer events. See more information here. 

ASUS X99 memory subsystem teardown

We received our ASUS X99 a few weeks back and immediately set it up in our lab to take a look at the DDR4 memory bus.  The first thing we all noticed was the fan on top of the processor.  It is very quiet.  In fact it is the quietest fan I think any of us has ever seen inside of a computer.  Onto the memory!  We got a hold of a 2 rank DDR4 DIMM from a vendor and plugged it in on top of our DDR4 DIMM Interposer that is attached to our FS2800 DDR Detective®  When we look at a memory bus we really look at it!  The eyes on the Address/Command and Control bus looked great at 1867MT/s and since they did we cranked it up to 2400MT/s.  So the DDR clock itself is 1.2GHz.  All is well and we were not failing any of the memory tests we threw at it including Memtest86, Google StressApp and ThirdIO's Nemesis.  We also used our U4154A logic Analyzer and our FS2510 Interposer to do eye scan and burst scan's on the DQ lines.  They looked great and completely jived with what our friends at Keysight were seeing.  BTW Keysight took it up a notch and clocked their ASUS X99 at 3.125GT/s and was able to successfully capture the DQ data signals.  See that announcement here.  So at first blush it looks like the folks at ASUS get a passing grade on thier first DDR4 implementation.

NIST get's into servers BIOS

Concern for our nations cloud infrastructure has caused the National Institute for Standards or NIST to get involved in BIOS updating.  See this article for more information.  In summary nefarious activity can take place if a servers BIOS is compromised.  NIST's ITL or Information Technology Lab has produced a special publication to give guidance on BIOS updates.