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The cache timing is not a physics phenomenon. It's an isolation phenomenon. Speculative execution is loading data into the cache, exactly as designed. The instr

The cache timing is not a physics phenomenon. It's an isolation phenomenon. Speculative execution is loading data into the cache, exactly as designed. The instructions that used the speculatively loaded cached data were not retired, exactly as designed. Requesting that cached data later (in actually retired instructions) is faster assuming it's still cached, which is a reasonable likelihood given the locality of the access. That's the timing attack vector. There's no physics here - it's all architecturally operating as designed. That's why the design has a security flaw, and there is no physics problem here. (There may be others, elsewhere, of course, but none in Spectre or Meltdown that I am aware of.)

mst 9y ago
From my POV "the locality of the access" making a speed difference is a physics phenomenon.
mannykannot 9y ago
The fact that is working as designed has no bearing on the question of whether it is a physics problem. You could just as well say (as Intel's press release seemed to to be trying to imply) that there isn't a fault at all, whether physical or not, because it is working as designed. But your own description of it working as designed is within the context of a state-machine model, and in that model, there is no attack vector; that only appears when you take the physics of the implementation into account. There wouldn't even be a cache except for the temporal physics of memory access. That it works as designed is beside the point because the design did not take the physics into account. Looking at it from the other direction, how do you conclude that rowhammer does exploit a physical phenomenon, without being inconsistent about what that means?