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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

#81

Earlier quoted context omitted.

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

Why would they do that?

I can't imagine why someone would hide details of the product they are selling. That is dishonest and should be illegal. Imagine if someone was selling food and would omit some ingredients from the list or you buy a house with a basement and you don't get a key nor info what's inside.

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

#83
post #43
post #30

Earlier quoted context omitted.

Plot twist: there’s been a few ME vulnerabilities. And who knows what other purposeful ME backdoors there may or may not be.

Sure, which is why this is useful to researchers. But the access someone needs to your system in order to exploit the ME vulnerabilities is sufficiently extreme that if someone achieves it you probably have other things to worry about.

I can't get with justifying one serious security problem using another. Attackers increasingly combine local privilege escalations to move laterally, but only need one RCE to get in.

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

#85

Earlier quoted context omitted.

Why would they do that?

I can't imagine why someone would hide details of the product they are selling. That is dishonest and should be illegal. Imagine if someone was selling food and would omit some ingredients from the list or you buy a house with a basement and you don't get a key nor info what's inside.

Quite the contrary, I suspect that telling the details would be illegal. The ME engine predates Snowden and is widely believed in the security community to be subject to NSA meddling. It may be that Intel is the recipient of a NSL preventing them from disclosing too many details.

But for whatever reason they have been very tight-lipped.

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

#86
post #54

Earlier quoted context omitted.

Hold up there you don't know if someone's been tampering with the trees, you'll have to grow your own forest first

The “trusting trust” flaw still applies, better sequence your own species of tree.

And trust the same chemical processes that eventually resulted in the mess we’re in? Start a new universe.

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

#87

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?

In most cases there is a public API which is documented and a private API which is not.

In this specific case, users do not have the ability to use this instruction, so there is no reason to document it.

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

#88

So, which CPUs are actually open-hardware and available to consumers with mainboards that support them? Is RISC-V going to be this?

None. Well, yeah, I think SiFive has HDL sources for quite a lot of their stuff up on GitHub, but it's not like you can just compile them into production silicon at home, heck, you can't even verify that the silicon was actually compiled from that source. (Yes there's research into verifiable silicon, but it's not like everyone has ultra high end electron microscopes and whatnot at home lol)

And of course nothing about RISC-V implies that production implementations will be open source at all.

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

#89
post #70

Earlier quoted context omitted.

The previous publicly known mechanism required signed updates. This mechanism allows anyone to twiddle the bits.

> This mechanism allows anyone to twiddle the bits. This remained unclear to me. Other comments say the CPU needs to be in red unlocked state, whatever that is. The screenshot shows UEFI. So one could guess the CPU is in such state before the operating system gets loaded. But the operating system typically loads a microcode update, after that the CPU should no longer be in unlocked state. So for "everyone can fiddle…

Firmware is not protected by Secure Boot. It can be protected by things like Boot Guard, but at least that one (Intel's) requires pairing the board and the CPU, so it can only be done in laptops and other prebuilt OEM systems.

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

#90

Earlier quoted context omitted.

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

In most cases there is a public API which is documented and a private API which is not. In this specific case, users do not have the ability to use this instruction, so there is no reason to document it.

Why is it acceptable for companies to keep such information away from a consumer?
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