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Comment by Afforess | Hacker News Reader

I don't agree, there is software that is designed to run on faulty hardware. This is often in high radiation environments (see: outer space). I agree this is not an area that much hardening has been done in conventional security models, but in other environments, it is common to use CRC error detection, parity information or other means to ensure that even if data is partially corrupted, that the original can be restored.

I see no reason to prevent someone from implementing this sort of error correction for GPG and other important cryptography.

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Hostile environments attack your software without intelligence. (When working with them, it may seem otherwise, but that's just cynicism.) Hostile people attack intelligently. Whatever mitigation you may imagine is possible by checking CRCs or something after the fact, you must account for the possibility that the software, the OS, or the CRC has also been attacked by a hostile intelligent adversary. The fact that we can make reliable software in the face of unintelligent attacks is not evidence that we can make secure software in the face of intelligent ones.

Rowhammer is too powerful a technique to expect secure software to run on machines affected by it. This is an attack based on using rowhammer to change bits in other VM's memory. The only sane response to that, from the perspective of writing secure software, is despair. You can't deal with attackers in possession of that primitive.

Rowhammer is largely random. You don't get to target specific bits of physical ram. You find scarce weak bits and work to get the data located there. In this case that means you can only pick a couple bits per 4KB to attack. That won't let you fake out a CRC.

That's where I'm getting a little hazy. The paper says the attacker can "induce bit flips over arbitrary physical memory in a fully controlled way." Sounds a little more advanced than "largely random" to me, and based on the article it sounds like FFS is a step up from "vanilla" Rowhammer...am I missing something?

Yeah, I mean if it won't beat a CRC wouldn't ECC RAM be a reasonably easy solution to this and wouldn't most servers already be secured against it?

ECC RAM makes it a harder, but three bit flips will still survive. It depends on whether the system actually acts properly when it sees a huge amount of ECC errors happening.

They can pick a bit or two per page to attack, but then they're stuck with those bits.

In theory they could attack a new bit every few minutes, but that requires a system that allows the victim page to be remapped multiple times. KSM does not; any other memory-merging system could work the same way to mitigate things.

Even if they could keep remapping, it's a very slow attack that way. Reloading the checksum every ten minutes would keep you safe.

This does not make sense. If an attacker an alter your data, he can alter your CRC codes as well. Or just replace the pointer to the checkCRC function to "return true".

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