On “I don't trust microcode” (2021) • Hacker News Board

Re: On “I don't trust microcode” (2021)

#51

Post by klelatti » Tue, Jan 31, 2023, 9:47 AM UTC

monocasa wrote: post #25

twisteriffic wrote: post #19

Earlier quoted context omitted.

> not microcoded Still microcoded, just not updatable. https://news.ycombinator.com/item?id=21428905

So I've reflected on my previous statements there, and have come to the conclusion that the 6502's PLA isn't microcode or a compression format for a microcode ROM. The big piece it's missing is the microinstruction address counter. There was a T state counter which was tripping me up, but having played with the visual 6502, the T state counter really isn't a full microinstruction addr counter. The PLA is really more…

> So the PLA really is more an encoding of random logic than a microcode ROM.

Thanks for a very succinct summary of a question I've pondered for a bit too.

Re: On “I don't trust microcode” (2021)

#52

Post by temptemptemp111 » Tue, Jan 31, 2023, 1:12 PM UTC

pjmlp wrote: post #10

DethNinja wrote: post #8

Earlier quoted context omitted.

There are good reasons to not trust microcode. For example, a certain instruction chain can be made to trigger backdoors on the CPU and allow direct memory access for attackers. Catching this might be rather hard, though definitely not impossible.

Same applies to CPUs without microcode due to hardware design bugs.

[dead]

Re: On “I don't trust microcode” (2021)

#53

Post by bo1024 » Tue, Jan 31, 2023, 3:05 PM UTC

ip26 wrote: post #38

bo1024 wrote: post #36

The article argues that one should trust microcode updates at least as much as the original microcode. Okay. But why would you trust microcode? It's closed source software running at the base layer of privilege and you have very little idea what it's doing or whether it's correct.

You could say that about the entire CPU. Original microcode should be trusted equal to the rest of the chip.

Yes, agree.

Re: On “I don't trust microcode” (2021)

#54

Post by amstan » Tue, Jan 31, 2023, 7:03 PM UTC

wmf wrote: post #29

The whole pop culture around open source firmware and Coreboot is a disaster based on posturing and misinformation. It's like an infosec version of anti-vaxxing. Unfortunately, educating people about specific facts won't help because they'll just move on to complaining about something else like Pluton.

Reminds me of that libreboot that targetted a very specific rk3288 chromebook (out of the 8 available) even through the original coreboot was blobless on all of them.

Re: On “I don't trust microcode” (2021)

#55

Post by phkahler » Tue, Jan 31, 2023, 8:51 PM UTC

brokenmachine wrote: post #47

phkahler wrote: post #34

Earlier quoted context omitted.

What if the main use of microcode is to provide certain customers custom instructions that the rest of us don't get. Perhaps the instructions themselves hint at algorithms that are not publicly known. That's not a threat to us, just secret instructions that can not be discovered.

An interesting suggestion, if rather fanciful. So we are to trust our entire security to implausible what if scenarios?

>> An interesting suggestion, if rather fanciful.

It has been shown that government agencies were ahead of public research in areas of (specifically) cryptography in the past, so it makes sense that they would still be ahead today (that is one of their goals too I think). There have also been instructions in processors that didn't make a lot of sense at the time, though I don't recall a specific example or what it was speculated to be for.

The only thing I think is fanciful is this being the primary reason to have microcoded instructions in the first place. I wouldn't be surprised at all if certain customers had access to special instructions via microcode updates.

Re: On “I don't trust microcode” (2021)

#56

Post by User23 » Tue, Jan 31, 2023, 11:07 PM UTC

gruez wrote: post #23

User23 wrote: post #17

Earlier quoted context omitted.

It looks like a used SEM can be had for the highish five figures on eBay. Someone who was good at YouTube and other social media could probably justify the expense. Of course there could be unintended consequences of having viral videos showing hardware backdoors in popular electronic devices.

>It looks like a used SEM can be had for the highish five figures on eBay What's the resolution on those like? Also, keep in mind that there's a lot more work to physically inspecting the CPU than just buying a SEM off ebay. You'd also need chemicals/equipment to etch through the different layers, as well the expertise to pull everything off.

Absolutely. And it's not as if the work of popularizing and profiting from that equipment and expertise is trivial either. Nevertheless, I reckon there's an opportunity there.