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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."
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.
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...
I'll go you one better - I have formed my own personal postulate/theory/law that:
No sufficiently complex system can ever be completely bug-free.
and it's corollary:
It is impossible to completely test a sufficiently complex system in every possible way to be certain that it's bug-free.
In that vein, someone once said "Foolproof is impossible because fools are so ingenious", and "As soon as an idiot-proof system is devised, they go and invent a better idiot!"
-- You are in a maze of little, twisty passages, all different... --