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Cool article. I didn't understand how the privilege escalation would be exploited. Obviously if the attacker already has access to the box, he can get root wi

by crucini 12y ago

Cool article. I didn't understand how the privilege escalation would be exploited. Obviously if the attacker already has access to the box, he can get root with this exploit. I think a chip backdoor could also be based on information leaking rather than executing arbitrary code. The steps would be: 1. Identify critical info, like crypto keys, from heuristics. This means keeping a special buffer, since you don't know at the beginning of an RSA operation that it's an RSA operation. The heuristics are not perfect, of course, but work with standard apps like Firefox, GPG and Outlook. 2. Exfiltrate the info. Via spread-spectrum RF, timing jitter in packets, or replacing random numbers in crypto. The article implies that since OSes and apps mix the hardware RNG with other sources, there's no point in subverting it. But the CPU can recognize common mix patterns, like in the Linux kernel, and subvert the final output. In this case the output entropy is good, but also leaks some secret to a listener who has the right keys.

treewash 12y ago
1. You design your CPU so whenever you execute an add instruction with $r1 = x, $r2 = y (say these are the add inputs), the next add instruction will switch to ring-0 mode and run code at address which is the result of the add. 2. You don't need access to the box. You just get the target to load a site with JS that sets x and y to those specfic values and adds them, and then adds zero to some address you want to execute (which you can aim to be shellcode in a JS string or something, but even if not there are a million tricks you can use to execute arbitrary code if you can run code at an arbitrary address). 3. Assuming the JS engine compiles sanely, you now have a way to control any computer and make it do anything via some JS on any web site. Ring-0 can totally bypass all virtualization and even the OS itself. And this exploit is so simple and powerful that everything else is a waste of time. No need to use statistical and entropy tricks to leak keys. You can own any computer with JS on a web site and steal anything you want from memory, including keys. And you can probably do this without the target noticing anything.
- TheLoneWolfling 12y ago
  If you're really being nasty you can potentially do this even without JS - say, by using CSS layout.
  - crucini 12y ago
    But can one predict how CSS will look to the CPU? Or do you assume a memcpy will happen at some point, and catch it then?
    - TheLoneWolfling 12y ago
      memcpy is one route. But, given that (almost) everyone runs browsers for which the binaries, at least, are avaliable, it's relatively straightforward to come up with something that triggers the vulnerability. And even if you don't know what browser they are using, you can make guesses. For example - if you have an image that's 102px wide and immediately to the right of an image that's 57px wide, at some point the CPU will probably add 57 and 102. Things like that.
- crucini 12y ago
  Sounds convincing. I'm not clear on the "million tricks" though. Suppose you embed some machine language in a string javascript, and use your r1/r2 trick - how can you compute the address of the machine language you want to execute? Or are you saying there are existing chunks of machine language in the OS or apps that would be useful to remote execute, with no arguments?

by crucini 12y ago

treewash 12y ago

1. You design your CPU so whenever you execute an add instruction with $r1 = x, $r2 = y (say these are the add inputs), the next add instruction will switch to ring-0 mode and run code at address which is the result of the add. 2. You don't need access to the box. You just get the target to load a site with JS that sets x and y to those specfic values and adds them, and then adds zero to some address you want to execute (which you can aim to be shellcode in a JS string or something, but even if not there are a million tricks you can use to execute arbitrary code if you can run code at an arbitrary address). 3. Assuming the JS engine compiles sanely, you now have a way to control any computer and make it do anything via some JS on any web site. Ring-0 can totally bypass all virtualization and even the OS itself. And this exploit is so simple and powerful that everything else is a waste of time. No need to use statistical and entropy tricks to leak keys. You can own any computer with JS on a web site and steal anything you want from memory, including keys. And you can probably do this without the target noticing anything.

TheLoneWolfling 12y ago
If you're really being nasty you can potentially do this even without JS - say, by using CSS layout.
- crucini 12y ago
  But can one predict how CSS will look to the CPU? Or do you assume a memcpy will happen at some point, and catch it then?
  - TheLoneWolfling 12y ago
    memcpy is one route. But, given that (almost) everyone runs browsers for which the binaries, at least, are avaliable, it's relatively straightforward to come up with something that triggers the vulnerability. And even if you don't know what browser they are using, you can make guesses. For example - if you have an image that's 102px wide and immediately to the right of an image that's 57px wide, at some point the CPU will probably add 57 and 102. Things like that.
crucini 12y ago
Sounds convincing. I'm not clear on the "million tricks" though. Suppose you embed some machine language in a string javascript, and use your r1/r2 trick - how can you compute the address of the machine language you want to execute? Or are you saying there are existing chunks of machine language in the OS or apps that would be useful to remote execute, with no arguments?