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Honest question: is AMD any better? Do they somehow manage to avoid Spectre / Meltdown without a slowdown?

by tomp 8y ago

simion314 8y ago
AMD is better, they are still affected by side channel attacks but they did not skipped on security checks and are not affected by speculative execution AFAIK https://www.amd.com/en/corporate/security-updates https://www.amd.com/en/corporate/security-updates
- coherentpony 8y ago
  > ...and are not affected by speculative execution AMD's chips definitely speculatively execute instructions. It's a common performance trick. AMD's chips also definitely throw an exception at retirement (of course) for instructions that attempt to load a privileged address, just like Intel's chips do. The difference is that when AMD's chips see a load instruction, the load isn't executed until it knows that the address isn't privileged. Intel's chips do execute the load (but then throw away the result when it realises the address was privileged). The speculative part is for instructions that depend on the result of the load.
  - simion314 8y ago
    >The difference is that when AMD's chips see a load instruction, the load isn't executed until it knows that the address isn't privileged. Intel's chips do execute the load (but then throw away the result when it realises the address was privileged) Thank you for the detailed explanation, can't we conclude that AMD engineering is more defensive then Intel, this is what I concluded.
    - coherentpony 8y ago
      Based on this datapoint? I don't think so. They're vulnerable to other side-channel attacks. Both AMD and Intel hire really smart people, but this stuff is really, really hard.
    - Symmetry 8y ago
      The general reaction from CPU designers I interact with online after this was that Intel engineers should have known the optimizations that enabled Meltdown were dangerous but that Specter was totally unforeseeable.
    - deleted 8y ago
      [deleted]
HeadsUpHigh 8y ago
Yes. Their arch is just different, they where not affected by meltdown and the chances of a spektre exploit actually working are very small. I don't know why that is the case but basically amd is 99% free from this story.
- repolfx 8y ago
  They aren't. Spectre works fine on AMD. They avoided Meltdown only because their cores are less optimised. Meltdown isn't Intel specific - Apple cores were also affected. It's clear that AMD weren't doing anything special w.r.t. side channel attacks. They were just further behind in the optimisation race and as a consequence, were less hit.
  - likeclockwork 8y ago
    Can you really call "fast but wrong/insecure" optimized?
    - mark-r 8y ago
      Yes you can, if it makes your benchmarks look better. That's why Intel is trying to suppress the benchmarks.
    - Dylan16807 8y ago
      It doesn't calculate anything wrong, so sure. For this particular optimization, it looks better not to have it. But in general, knowing how something is flawed lets you mitigate the flaws. We use floating point despite it being mathematically wrong, because it's fast and we can mitigate the wrongness. I could imagine a chip where speculation could be toggled between different modes, if there was enough demand. I will say that "just further behind" is probably wrong. AMD has a lot of optimizations in their chips. They have safer ones, which might be luck or might be engineering talent, but it's not a mere artifact of being behind the curve.
  - kllrnohj 8y ago
    That is a horrifically biased & wrong summary. AMD enforce privilege checks at access time rather than at retirement time. Whether or not this is due to "lack of optimization" or "good security engineering" nobody knows. But your claims that this was purely the result of "less optimised [sic]" cores is nonsense. You have zero evidence whatsoever that that was the case vs. AMD just having superior engineering on this particular aspect and not adding bugs to their architecture. All we know are that Intel & ARM CPUs have an entire category of security bugs that AMD don't, and that upon close analysis AMD's CPUs are operating in a more secure foundation.
guipsp 8y ago
AMD are not employing these anti-competitive practices (at least at the moment).
- LeifCarrotson 8y ago
  I think GP was asking not about the anticompetitive practices but about the actual exploit that Intel is responding to. But you make a good point. Intel has two faults: one, they made a significant mistake in their chip design, and two, they responded to criticism poorly. AMD did not make the mistake and has responded well to criticism.

Honest question: is AMD any better? Do they somehow manage to avoid Spectre / Meltdown without a slowdown?

by tomp 8y ago

Honest question: is AMD any better? Do they somehow manage to avoid Spectre / Meltdown without a slowdown?

AMD is better, they are still affected by side channel attacks but they did not skipped on security checks and are not affected by speculative execution AFAIK https://www.amd.com/en/corporate/security-updates https://www.amd.com/en/corporate/security-updates

coherentpony 8y ago
> ...and are not affected by speculative execution AMD's chips definitely speculatively execute instructions. It's a common performance trick. AMD's chips also definitely throw an exception at retirement (of course) for instructions that attempt to load a privileged address, just like Intel's chips do. The difference is that when AMD's chips see a load instruction, the load isn't executed until it knows that the address isn't privileged. Intel's chips do execute the load (but then throw away the result when it realises the address was privileged). The speculative part is for instructions that depend on the result of the load.
- simion314 8y ago
  >The difference is that when AMD's chips see a load instruction, the load isn't executed until it knows that the address isn't privileged. Intel's chips do execute the load (but then throw away the result when it realises the address was privileged) Thank you for the detailed explanation, can't we conclude that AMD engineering is more defensive then Intel, this is what I concluded.
  - coherentpony 8y ago
    Based on this datapoint? I don't think so. They're vulnerable to other side-channel attacks. Both AMD and Intel hire really smart people, but this stuff is really, really hard.
  - Symmetry 8y ago
    The general reaction from CPU designers I interact with online after this was that Intel engineers should have known the optimizations that enabled Meltdown were dangerous but that Specter was totally unforeseeable.
  - deleted 8y ago
    [deleted]

HeadsUpHigh 8y ago

Yes. Their arch is just different, they where not affected by meltdown and the chances of a spektre exploit actually working are very small. I don't know why that is the case but basically amd is 99% free from this story.

repolfx 8y ago
They aren't. Spectre works fine on AMD. They avoided Meltdown only because their cores are less optimised. Meltdown isn't Intel specific - Apple cores were also affected. It's clear that AMD weren't doing anything special w.r.t. side channel attacks. They were just further behind in the optimisation race and as a consequence, were less hit.
- likeclockwork 8y ago
  Can you really call "fast but wrong/insecure" optimized?
  - mark-r 8y ago
    Yes you can, if it makes your benchmarks look better. That's why Intel is trying to suppress the benchmarks.
  - Dylan16807 8y ago
    It doesn't calculate anything wrong, so sure. For this particular optimization, it looks better not to have it. But in general, knowing how something is flawed lets you mitigate the flaws. We use floating point despite it being mathematically wrong, because it's fast and we can mitigate the wrongness. I could imagine a chip where speculation could be toggled between different modes, if there was enough demand. I will say that "just further behind" is probably wrong. AMD has a lot of optimizations in their chips. They have safer ones, which might be luck or might be engineering talent, but it's not a mere artifact of being behind the curve.
- kllrnohj 8y ago
  That is a horrifically biased & wrong summary. AMD enforce privilege checks at access time rather than at retirement time. Whether or not this is due to "lack of optimization" or "good security engineering" nobody knows. But your claims that this was purely the result of "less optimised [sic]" cores is nonsense. You have zero evidence whatsoever that that was the case vs. AMD just having superior engineering on this particular aspect and not adding bugs to their architecture. All we know are that Intel & ARM CPUs have an entire category of security bugs that AMD don't, and that upon close analysis AMD's CPUs are operating in a more secure foundation.

guipsp 8y ago

AMD are not employing these anti-competitive practices (at least at the moment).

LeifCarrotson 8y ago
I think GP was asking not about the anticompetitive practices but about the actual exploit that Intel is responding to. But you make a good point. Intel has two faults: one, they made a significant mistake in their chip design, and two, they responded to criticism poorly. AMD did not make the mistake and has responded well to criticism.