Demystifying the Secure Enclave Processor [pdf]

Post by tptacek » Fri, Aug 05, 2016, 9:16 PM UTC

Analemma_ wrote: post #15

zellyn wrote: post #10

Am I understanding correctly that while they enumerate a list of potentially useful attack vectors, there are no actual attacks (yet)? Of course, since the Year of Snowden, I now assume that any "theoretical" attack vector has a Team, a Project Manager, and a half-completed Kanban board somewhere deep in the NSA…

If I'm reading the last few slides correctly, the tl;dr is something like: - They haven't found any actual attacks. - Because the secure enclave runs so little code, there's very little attack surface in software, and much of what there is (mainly message passing between the secure and normal environments) seems solid. The only likely possibility is the wrapper code around IMG4. - However, if there is an exploit in I…

Post by kevincox » Fri, Aug 05, 2016, 10:56 PM UTC

Post by tptacek » Sat, Aug 06, 2016, 7:45 PM UTC

kevincox wrote: post #23

This seems like a lot of code to be running in a security-critical relatively simple device. Does anyone else have the impression that I would rather this device be much, much simpler. Of course that might raise development costs but that seems like a fair trade off in this case, especially if it causes some "features" not to be implemented because they would be too hard.

Post by tptacek » Sat, Aug 06, 2016, 8:01 PM UTC

kevincox wrote: post #26

tptacek wrote: post #25

Earlier quoted context omitted.

What "lot of code"? It's running L4, which is perhaps the simplest operating system that still deserves the name. A lot of the complexity they're documenting is in hardware: the AES-XEX memory encryption scheme that protect's SEP's memory from the AP (or any other component of the system), the fuse array that controls its settings, the memory filter that restricts AP reads/writes to the mailbox range. Still more of t…

I guess I would have expected it to not have an operating system. I understand that and operating system can provide security through isolation but when you are running small amounts of highly security critical code it seems like the isolation benefit would be outweighed by the extra attack surface. Everything is a trade off I guess...

Post by tptacek » Sat, Aug 06, 2016, 9:30 PM UTC

kevincox wrote: post #28

tptacek wrote: post #27

Earlier quoted context omitted.

Can you be more specific about the extra attack surface to which you're referring? What vantage point does an attacker need to have to target that attack surface?

Well most data is going through more layers of code. And as a rough approximation the more code running the more vulnerabilities. I guess this "internal" code isn't as critical of a surface because you have to get through the applications but there is certainly still risk.