Earlier quoted context omitted.
Don't use CPUs from companies.
Don't use anything
Don't be so paranoid. Just build your own CPU from discrete NAND gates like everyone else.
Undocumented x86 instructions in Intel CPUs that can modify microcode
31–40 of 145 posts
Re: Undocumented x86 instructions in Intel CPUs that can modify microcode
#32The Chinese and other state actors may have already dug it up, or been provided it.
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Re: Undocumented x86 instructions in Intel CPUs that can modify microcode
#33Can it be used to make RDRAND always return the same number?
Nah. Just use an AMD Ryzen for that: https://almonde.org/posts/how-to-check-for-rdrand-bug-on-ryz...
Re: Undocumented x86 instructions in Intel CPUs that can modify microcode
#34Re: Undocumented x86 instructions in Intel CPUs that can modify microcode
#35The 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...
The keys are stripped out if you put it into the required unlock
mode.
Re: Undocumented x86 instructions in Intel CPUs that can modify microcode
#36Now the question is "What does the microarchitecture really look like so we can write our own x86 microcode?"
Re: Undocumented x86 instructions in Intel CPUs that can modify microcode
#37The 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…
>It wasn’t even that long ago that ucode wasn’t even encrypted with integrity
whether they're encrypted or not doesn't really matter. what actually matters is whether they're signed or not. There was a talk given in 2017 about trying to modify the microcode in AMD processors, but they were using processors from a decade ago (AMD K10, introduced 2007). That makes me think that processors made in the past decade are probably using signed microcode.
Re: Undocumented x86 instructions in Intel CPUs that can modify microcode
#38Nothing 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?
Yes! God, I miss tge days when things actually shipped with manuals on how everything works. I have a fiew old pieces of hardware I keep manuals around for just to remind me of what the writing style is supposed to look like.
Re: Undocumented x86 instructions in Intel CPUs that can modify microcode
#39Earlier quoted context omitted.
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…
>It wasn’t even that long ago that ucode wasn’t even encrypted with integrity whether they're encrypted or not doesn't really matter. what actually matters is whether they're signed or not. There was a talk given in 2017 about trying to modify the microcode in AMD processors, but they were using processors from a decade ago (AMD K10, introduced 2007). That makes me think that processors made in the past decade are pr…
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Re: Undocumented x86 instructions in Intel CPUs that can modify microcode
#40Earlier quoted context omitted.
Don't be so paranoid. Just build your own CPU from discrete NAND gates like everyone else.
A pen and paper is everything you need.
But what if it’s some of that fancy paper or a pen that records everything you write! Might need to manufacture your own pen and paper now...