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Flawed AMD Chip Can Lead To Data Corruption
Brandonski writes "Apparently AMD allowed some flawed chips to slip through their detection grid. The problem affects only a small number of chips and only single core 2.6 and 2.8 GHz CPUs." From the article: "It is believed that the glitch is triggered when the affected chip's FPU is made to loop through a series of memory-fetch, multiplication and addition operations without any condition checks on the result of the calculations. The loop has to run over and over again for long enough to cause localized heating which together with high ambient temperatures could combine to cause the result of the operation to be recorded incorrectly, leading to data corruption."
Hey, I have an AMD 2.8Ghz. Maybe I should stop refresðN9'óI]öR9ù¥Î6ýPoe}+èa(ê{
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I'm too young to remember the details (I think it goes back to the early eighties at least), but perhaps some of the elder gods that lurk around here might be able to supply more details.
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The big question is will someone write malware/virus to somehow take advantage of this flaw?
I am curious how a virus could possibly exploit this. It would have to a) hog the resources so that it ran nearly exclusively, which would mean the virus already had control, and b) somehow cause a floating point error to result in a priviliages error. (priviliages and security routines rarely use floating point numbers). Also why would a kernel patch be released for this? It would hurt performance for the rest of us, customers with defective chips should simply return and replace them.
Philosophy.
Wow! AMD has invented a way to crash an infinite loop! Awesome! Intel? I bet their solution will take twice as long to crash this loop:
10 PRINT "HELLO WORLD"
20 GOTO 10
AMD is always innovating.
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"The company is also working with OEMs to identify affected parts and contact customers who could be affected - if they are, they will be offered free replacements."
forth paragraph in TFA.
Not likely. This is valid user code that is being executed. On other CPUs, the same code wouldn't cause a problem. Something like the F00F bug is fixable in the kernel by mucking with exception handler. This is pure user-land code.
Do you even lift?
These aren't the 'roids you're looking for.
This is different than the Intel bug; that was a logic flaw, where the chip computed a floating point quantity using an incorrect algorithm. This is an implementation error. In fact, the article mentions that they're going to re-spec the parts and they'll be fine. So if you've got a 2.8Ghz part, and you run this loop at 2.8Ghz (within the old spec), it's like you're "overclocking" (because you're actually outside of AMD's new spec). My guess is that if you over-bought your heatsink and got something better than the stock OEM cooling solution, you would be fine even if you ran this loop all day. Yay, arctic silver!
No CPU can guarantee to be free of corruption, the goal of the designer is just to minimize the likelihood of corruption. The design margins are usually such that proper operation is ensured, except for the statistical outliers. However, even CPUs with several error checking and correcting mechanisms can still corrupt data, it is just extremely unlikely. A CPU can never know for sure if it can compute a result accurately, or if an operation was performed correctly, just like no communications system can achieve bit error rates of 0.
Data corruption in integrated circuits can come from several different sources. Cosmic rays are likely to alter memory values, especially so in DRAM cells. Typically, only ICs for space applications are actually radiation hardened. Much less likely, transistor device noise can corrupt data. Transistor device noise is usually more an issue in RF circuits. Finally, not all manufacturing defects can be found during manufacturing test, since most test sequences don't even achieve 100% fault coverage under currently used fault models, and this does not even consider how closely the models represent the actually circuit failure modes.
Really, for most people this floating point data corruption is probably a non-issue. It is even more unlikely that errors in floating point data lead to exploits. It is more likely that some bits of your DRAM memory will get corrupted. On my system with ECC RAM that is a few years old, logs show that I get about 1 or 2 (correctable) errors per day...
Having read a lot about this flaw it's actually amazing that AMD's quality control found the problem in the first place.
The actions needed to cause the problem to arise are so extreme that they'd never happen in the field. i.e. Loop through tight floating-point only instructions without any comparisons for maybe hours before the error occurs.
This would *NEVER* happen in the field. Firstly, in any modern OS the process would have been pre-empted long before any problem could occur (causing other instructions to run and hence stopping the overheating). Secondly, no real-world program would ever do this sort of thing as there would always be a comparison in the loop within the timeframe.
This is a theoretical problem only in the real world, especially as it only affects about 3000 processors in total (it has been quoted). This is why AMD gave it such a low priority. We should just forget about it and move on.
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Some of the tendering spreadsheets i've seen for a few companies i've worked for have had quite a lot of calculation going on in them - change a few cells that others depend on that have others depending on them, etc.... do that all day, it adds up quick.
You only need 1 of those operations in that instance to screw up and you could be down a few million dollars, if it's not picked up.
Even forgetting that it's just the moral thing to do...Risk vs replacement cost = no brainer. If only 3000 cpus are affected at say $300 each for amd to sell retail (i'm sure their cost is FAR less), they'd be mad not to just do it (maybe even offer a free speed bump) and reap the positive PR.
All it needs is for ONE company to blame a budget blowout on them and it's well and truly paid for...
smash.
I run: Windows, OS X, Linux, FreeBSD. Just because you have a hammer, doesn't mean everything is a nail.
If you have any interrupts coming in, or your loop has a termination condition. I think you have to have your hardware set to send an interrupt many hours in the future then start an otherwise nonterminating loop.
So under normal conditions on normal PC hardware, this simply won't happen.
Of course, I expect AMD's production testing dept to have far better code, since they will devote more job hours to it and know proprietary chip details. Still, different parts of AMD as emailed me several times to thank me because they found the pgms useful. Great.
But these guys know what they're doing. Heat transfer from the hot multipliers has to be carefully analysed [3D finite element heat transfer analysis]. I suspect something far more mundane, like someone reducing die or slug thickness, or a mfg problem with the die/slug gap or thermal goop.