3 ms·

The reason is that floating point instructions are executed on a separate unit (the FPU), with a separate decoder. I don't think that has been true for a very

The reason is that floating point instructions are executed on a separate unit (the FPU), with a separate decoder. I don't think that has been true for a very long time. If the backdoor depends on some "magic values", it would be relatively easy to spot just by looking at the microcode. The problem with both your theory and the article's theory is that nobody outside the chip companies themselves really knows how the microcode works. This reduces both the people who could pull off such a backdoor and the people who could discover it to a very small number. A similar thing applies to your point about changes during manufacturing. Overall, this means that CPU backdoors are a thing to be concerned about, keeping in mind that it's probably a technique that will, for a long time, be limited to the kind of people who were responsible for Stuxnet.

sliverstorm 12y ago
I don't think that has been true In support of that: http://www.xbitlabs.com/images/news/2009-11/amd_bulldozer_scheme.jpg http://www.xbitlabs.com/images/news/2009-11/amd_bulldozer_sc...
tomerv 12y ago
There are so many people involved in the design and manufacturing of a processor, that I don't see how it's possible to hide a backdoor, either in the microcode or during manufacturing. We're not talking about some secret government agency, we're taking about a place with many workers around the world, with different agendas. Eventually someone will find about about the backdoor and leak information about its existence.
- Tuna-Fish 12y ago
  > There are so many people involved in the design and manufacturing of a processor, that I don't see how it's possible to hide a backdoor, either in the microcode or during manufacturing. We're not talking about some secret government agency, we're taking about a place with many workers around the world, with different agendas. However, the end result of both CPU design and the microcode team is essentially unreadable. No-one outside Intel can read their microcode updates, as they are obfuscated in some way, possibly encrypted. This means that compromising just the last step, the people or tools doing the obfuscating, means you can output whatever you want with no-one on the team being able to find it out. The same is true for the CPU design. Created masks are generally not looked at, other than to verify small spots if it seems there are bugs. Because of this, compromising the last step between the model and the mask would allow you to output whatever you want with no-one of the thousands of the people working on it ever finding out.
- crucini 12y ago
  This is a very interesting topic - how much can we rely on the tendency of people to leak. I notice that despite the thousands who have worked for Intel, virtually no Intel confidential material has been leaked. At least, that I'm aware of. People value their careers and houses, and I'm sure Intel threatens employees with consequences for leaking.

sliverstorm 12y ago

I don't think that has been true In support of that: http://www.xbitlabs.com/images/news/2009-11/amd_bulldozer_scheme.jpg http://www.xbitlabs.com/images/news/2009-11/amd_bulldozer_sc...

tomerv 12y ago

There are so many people involved in the design and manufacturing of a processor, that I don't see how it's possible to hide a backdoor, either in the microcode or during manufacturing. We're not talking about some secret government agency, we're taking about a place with many workers around the world, with different agendas. Eventually someone will find about about the backdoor and leak information about its existence.

Tuna-Fish 12y ago
> There are so many people involved in the design and manufacturing of a processor, that I don't see how it's possible to hide a backdoor, either in the microcode or during manufacturing. We're not talking about some secret government agency, we're taking about a place with many workers around the world, with different agendas. However, the end result of both CPU design and the microcode team is essentially unreadable. No-one outside Intel can read their microcode updates, as they are obfuscated in some way, possibly encrypted. This means that compromising just the last step, the people or tools doing the obfuscating, means you can output whatever you want with no-one on the team being able to find it out. The same is true for the CPU design. Created masks are generally not looked at, other than to verify small spots if it seems there are bugs. Because of this, compromising the last step between the model and the mask would allow you to output whatever you want with no-one of the thousands of the people working on it ever finding out.
crucini 12y ago
This is a very interesting topic - how much can we rely on the tendency of people to leak. I notice that despite the thousands who have worked for Intel, virtually no Intel confidential material has been leaked. At least, that I'm aware of. People value their careers and houses, and I'm sure Intel threatens employees with consequences for leaking.