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Undocumented x86 instructions in Intel CPUs that can modify microcode

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Re: Undocumented x86 instructions in Intel CPUs that can modify microcode

#11

Post by strstr »

mjg59 wrote: post #2

The followup tweet indicates that the CPU has to be in an unlocked state before this is possible, which on a typical system requires there to be a Management Engine vulnerability first. Given what we currently know, this is going to be interesting for people interested in researching the behaviour and security of Intel CPUs and might well lead to discovery of security issues in future, but in itself I don't think thi…

This seems like yet another thing on the list of “x86 hardware issues that sound worse than they are”.

I’m interested to see what people are able to reverse engineer with these sorts of tools. It wasn’t even that long ago that ucode wasn’t even encrypted with integrity. I don’t think AMD started doing that until around 2010.

I’m also curious which hardware versions this works on, since it’s not obvious it’s universal. I’ll be amused if it’s some forlorn low power chip from 10 years ago.

Re: Undocumented x86 instructions in Intel CPUs that can modify microcode

#12

Post by yjftsjthsd-h »

intricatedetail wrote: post #9
yjftsjthsd-h wrote: post #5

Nothing against the original post (which just says what they found), but this seems to be really overblown. Yes, of course Intel has instructions to update the micro code, since that's a thing that they do. Neither is it particularly surprising that they didn't bother to document operations that only they would ever have reason to use (in their eyes). If, as sibling comment notes, you have to be in a specific unlocke…

Should products be fully documented so that consumers can make an informed decision?

I don't know. It's Windows vs Linux all over; I think Open is better, but Intel has never (AFAIK) pretended to do that. If a customer knows "Intel/Microsoft controls this", I personally feel like that's an acceptable tradeoff. And for people who find that unacceptable, there's Debian on POWER9. But if you're picking Intel, it's not like these opcodes change anything; we already have ME sitting there controlling the machine.

Re: Undocumented x86 instructions in Intel CPUs that can modify microcode

#13

Post by intricatedetail »

yjftsjthsd-h wrote: post #12
intricatedetail wrote: post #9

Earlier quoted context omitted.

Should products be fully documented so that consumers can make an informed decision?

I don't know. It's Windows vs Linux all over; I think Open is better, but Intel has never (AFAIK) pretended to do that. If a customer knows "Intel/Microsoft controls this", I personally feel like that's an acceptable tradeoff. And for people who find that unacceptable, there's Debian on POWER9. But if you're picking Intel, it's not like these opcodes change anything; we already have ME sitting there controlling the m…

Did they release specs so that customer could build their own ME to manage the CPU? That would be interesting.

Re: Undocumented x86 instructions in Intel CPUs that can modify microcode

#14

Post by dooglius »

mjg59 wrote: post #2

The followup tweet indicates that the CPU has to be in an unlocked state before this is possible, which on a typical system requires there to be a Management Engine vulnerability first. Given what we currently know, this is going to be interesting for people interested in researching the behaviour and security of Intel CPUs and might well lead to discovery of security issues in future, but in itself I don't think thi…

This would still break SGX/remote attestation, no? The chip can correctly say it's running some piece of assembly but if "ret" has been redefined to do whatever I want...

Re: Undocumented x86 instructions in Intel CPUs that can modify microcode

#17

Post by userbinator »

bedros wrote: post #16

Good thing Apple is moving to M1; no more of that Intel crap. and stick with AMD for Linux.

I wonder what interesting things are in Apple's completely undocumented chips? There is that famous saying about known unknowns and unknown unknowns...

Re: Undocumented x86 instructions in Intel CPUs that can modify microcode

#18

Post by userbinator »

dooglius wrote: post #14
mjg59 wrote: post #2

The followup tweet indicates that the CPU has to be in an unlocked state before this is possible, which on a typical system requires there to be a Management Engine vulnerability first. Given what we currently know, this is going to be interesting for people interested in researching the behaviour and security of Intel CPUs and might well lead to discovery of security issues in future, but in itself I don't think thi…

This would still break SGX/remote attestation, no? The chip can correctly say it's running some piece of assembly but if "ret" has been redefined to do whatever I want...

That would be a good thing, given what those features are usually used for (DRM and other user-hostility).

Re: Undocumented x86 instructions in Intel CPUs that can modify microcode

#19

Post by sodality2 »

dooglius wrote: post #14
mjg59 wrote: post #2

The followup tweet indicates that the CPU has to be in an unlocked state before this is possible, which on a typical system requires there to be a Management Engine vulnerability first. Given what we currently know, this is going to be interesting for people interested in researching the behaviour and security of Intel CPUs and might well lead to discovery of security issues in future, but in itself I don't think thi…

This would still break SGX/remote attestation, no? The chip can correctly say it's running some piece of assembly but if "ret" has been redefined to do whatever I want...

This is what I'm interested in since they pushed that so heavily.
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