Looks like I'm getting the final kick to Linux on my main gaming PC.

when the new kernel comes out Linux users will be safe

It’s going to take a lot longer than that for most distros to move to latest upstream. This specific fix might be pulled in as a hotfix if you’re lucky, but it still takes time. The latest Ubuntu LTS is on 5.15, for example, which was released in October 2021. Debian Bookworm, which just released last month, uses 6.1 from December 2022.

Time to sit back and relax

That's because of monopolies... There are only two brands of PC CPUs you could own...

Well, this happens to affect the Ryzen 5 3600, which I'm pretty sure is one of AMD's most popular processors ever....so you're certainly not alone.

That's a very bad idea.

The bad news is that the exploit doesn't require physical hardware access and can be triggered by loading JavaScript on a malicious website.

It's worth noting these are the firmware / microcode fixes.

There's already a software solution available,

There is a software workaround, you can set the chicken bit DE_CFG[9]. This may have some performance cost, and the microcode update is preferred.

source: https://www.openwall.com/lists/oss-security/2023/07/24/3

AMD has also already released a fix for the big boy - the EPYC processor.

The more steps in the instruction pipeline the more ways there are for there to be an error where some result doesn't get erased when undoing stuff from the wrong branch. It's basically like telling someone to move into a new house and get settled then stopping them six hours in and trying to make sure you get all their stuff out.

It wasn't branch prediction alone, it was the cache combined with branch prediction. The problem is that even discarded outcomes fill the cache with data. Those older vulnerabilities also had the problem that the access permissions check was done after the branch prediction. It's probably too expensive to do when it's not even clear yet whether the branch is going to be taken (that's just speculation on my part though).

I've got an older 3900X that's Zen 2, but I'm otherwise clear, too.

It's kind of hard to figure out which Zen # a CPU falls under, so here's the Wiki page listing all Zen 2 CPUs.

The guys themselves made a pretty good write-up. https://lock.cmpxchg8b.com/zenbleed.html

The short version is that the very large registers on the modern CPUs aren't fixed things like they used to be, they're allocated from some register area on the die. When they "zero" the upper portion of one of the large registers it doesn't really clear it. It just releases the block back to available.

Another thing all CPUs need these days to keep fast is branch prediction. CPUs are only fast if they can keep the pipeline of upcoming commands (opcodes) to process full. So they often run both possible routes for a branch and discard the loser.

In this case they "trick" the CPU by asking it to "clear" a block of one of these large registers (the upper half). But then have the branch go the other way. What sometimes happens is that the register space is "released" but it has to take it back. In some specific circumstances they are able to have the register come back, but not with the original contents but with some random contents of maybe another register that was used by another thread (maybe even running on a different VM guest).

I have a server with a 3000 series CPU. I can confirm this definitely works. You'll get all kind of random blocks of memory from processes running as all users (and kernel code). For AMD processors running VM servers it is even worse. Because if you have say a VPS running on an AMD Zen2 CPU, you can login as any user run this and get random data from people on other VPS on the same hardware!

There is a linux workaround, and it seems most CPUs will be fixed by December.

Note: If you have access to a VPS that is vulnerable, do note that in most countries it is illegal to even try to exploit this.

They've had a couple. Spectre is the one to which you're referring, I bet.

A CPU performs operations like "read a small bit of thing from the memory into the CPU" and "do a small bit of computation on things inside the CPU" and "put a small bit of thing from the CPU into the memory".

Doing small bits of computation on things inside the CPU is very fast but moving bits of things from or to the memory is slow in comparison. In order to not be slowed down, CPUs read the code ahead of what is currently being executed, and try to guess what is going to happen and what will need to be moved from the memory into the CPU, so they can do it ahead of time, and have the small bit of thing from the memory already available right there in the CPU when it's time to do a bit of computation on it. That way, there is no need to wait on slow memory, and the CPU runs much faster overall. That's a good thing.

In this case, a researcher found a way to make certain CPUs guess what is going to happen with the code wrong, in such a way that the small bits of things that were read from the memory ahead of time do not get properly cleaned up, and can still be found inside the CPU by another program. Those small bits of things might be your password or banking details, so that's bad.