alt Hacker NewsOne thing I don't understand about security issues. If you look at the physics the rowhammer "bug" is not a cpu flaw, and not really a memory flaw either. This was known when capacitor based memory was invented, and was put forward as a disadvantage in the very first designs. It's physics. If you do any kind of DDR ram (including, I think, HBM), there is no way to avoid rowhammer-style bit flips. And fixed systems ... aren't fixed. Not even fixed systems currently being built.
Capacitor based memory will be, and will remain, vulnerable to this. Capacitors being charged and discharged will generate radio waves and radio waves will change the state of other capacitors. There is no avoiding this, there is only minimizing it, and at the scales we're talking about, there's only minimizing it somewhat.
There are probably a lot of patterns we haven't seen yet. Like memory write patterns that change other memory by having the waves interfere.
You can only make it more difficult by thinking better about memory layout, and change it a bit by thinking about the physical layout of memory cells. But you're only changing the patterns. It's not possible to prevent it. You cannot fix this. Not now, not yesterday, not in 100 years.
It's currently too difficult for human to think about (even though people are slowly publishing about yet another system being vulnerable to rowhammer style attacks that work a little different from the existing ones)
So why isn't it "game over", at least for the web, for phones and apps, for ...? That bug isn't solved an nothing short of switching everything to SRAM, at incredible cost, will fix it, not just in legacy systems, but new systems too, now and in the future.
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Rowhammer is most certainly a hardware flaw. DRAM manufacturers have pushed cells too close together to meet the specifications claimed on their datasheets. Increasing cell sizes would be the correct hardware fix for the issue. Engineering is accepting the reality of physics to build things that are useful.
Unfortunately, we live in a world where the few percentage points on the production cost of DRAM needed to completely mitigate rowhammer is sufficient to ensure that defective DRAM continues to be sold well after the industry became aware of the problem. This is one of the instances where a class action lawsuit might actually do some good.
Security works by layers.
The physics makes the rowhammer impossible to fix in practice, but you can add various mitigations: scrambling, ECC, detection and response, etc... On the application level, you can also make it so that it is not possible to do a rowhammer in the first place. Fix everything that can be fixed and mitigate what can't be fixed.
And there is another security issue that can't be fixed, and is much worse than rowhammer: people. But we can't remove people, just like we can't remove DRAM for the performance level we need, so we mitigate the risk. It is not game over because we have other layers of security.
Because software defects are more common, easier to exploit, faster to exploit, cheaper to find, and massively more consistent to leverage.
If software improved to the degree that hardware and physics-level exploits were the easier, we would be in a world 100x more secure than what we have now.
The real question you should be asking is why is it not “game over” right now given that most people would only hope in their wildest dreams that they would be so lucky that worrying about Rowhammer and the like would be a good use of time compared to the other much larger gaping software holes.