[PhilipRoman]

My personal opinion is that we should solve it the opposite way - don't run untrusted code in the first place (with rare exceptions like dedicating an entire cpu core and a region of memory to a virtual machine, etc). Speculation is one of many side channel attacks, who knows what kind of crazy RF-based exploits are out there. AFAIK we still haven't fully solved rowhammer.

I think for "normal" users the main risk is JavaScript, which can (kind of) be mitigated in software without affecting the rest of the system, so no one really cares about these attacks. But the fundamental abstraction leak between physics and programming will always be there.

[mort96]

OpenSSL is "trusted code". The problem isn't that OpenSSL is doing something nefarious, but that the CPU breaks assumptions it makes about how one can write constant-time algorithms.

[tsimionescu]

But the problem is not OpenSSL, it's that malicious code on the system can read the keys OpenSSL is using. If you don't run malicious code on the same system as OpenSSL, this attack goes away - there's no way to run a CPU timing attack from a different network.

[jval43]

"Remote Timing Attacks Are Practical" (2003):

https://crypto.stanford.edu/~dabo/papers/ssl-timing.pdf

That's on the local network. I remember a paper doing this over the internet, but couldn't find it. A similar one over the internet:

https://www.usenix.org/conference/usenixsecurity20/presentat...

But in practice it's going to be malicious JS running in your browser: https://www.schneier.com/blog/archives/2021/03/exploiting-sp...

[mort96]

From what I understand, the problem is that algorithms which should be constant time are actually taking a variable amount of time depending on the data. If I have some server software whose security depends on those constant-time algorithms actually being constant time, why shouldn't this be exploitable over the network?

[DougBTX]

The mechanism is described in the FAQ here: https://gofetch.fail

> The GoFetch attack is based on a CPU feature called data memory-dependent prefetcher (DMP), which is present in the latest Apple processors. We reverse-engineered DMPs on Apple m-series CPUs and found that the DMP activates (and attempts to dereference) data loaded from memory that "looks like" a pointer. This explicitly violates a requirement of the constant-time programming paradigm, which forbids mixing data and memory access patterns.

> To exploit the DMP, we craft chosen inputs to cryptographic operations, in a way where pointer-like values only appear if we have correctly guessed some bits of the secret key. We verify these guesses by monitoring whether the DMP performs a dereference through cache-timing analysis. Once we make a correct guess, we proceed to guess the next batch of key bits. Using this approach, we show end-to-end key extraction attacks on popular constant-time implementations of classical (OpenSSL Diffie-Hellman Key Exchange, Go RSA decryption) and post-quantum cryptography (CRYSTALS-Kyber and CRYSTALS-Dilithium).

It sounds like the OpenSSL code is still constant time (it doesn't expect pointers in the intermediate values, to OpenSSL it is just data, not something it will ever dereference) but the attacker-controlled "monitoring" code's runtime changes based on whether the DMP ran or not.

If that's right, then the attacker still needs to run their monitoring code on the target, it isn't sufficient to just run OpenSSL etc itself.

Edit: it is more explicit in the paper, they assume that OpenSSL (the victim) is still constant time:

> In this paper we assume a typical microarchitectural attack scenario, where the victim and attacker have two different processes co-located on the same machine.

> For our cryptographic attacks, we assume the attacker runs unprivileged code and is able to interact with the victim via nominal software interfaces, triggering it to perform private key operations. Next, we assume that the victim is constant-time software that does not exhibit any (known) microarchitectural side-channel leakage. Finally, we assume that the attacker and the victim do not share memory, but that the attacker can monitor any microarchitectural side channels available to it, e.g., cache latency.

[mort96]

Thanks for the details, I concluded more or less the same: https://news.ycombinator.com/item?id=39789307

[tsimionescu]

Because the timing difference is extraordinarily subtle, far too small to measure compared to regular network timing noise.

[mort96]

Noise doesn't protect against that, statistics is a thing.

But I think you might overall be right that this requires two colocated processes: the paper talks about how the DMP breaks assumptions made by "the constant-time programming model", and I took this to mean that constant-time algorithms aren't constant-time any more. Reading more closely, I think maybe the issue is that "the constant-time programming model" was also assumed to make secrets safe from cache timing side-channels leaking the secrets to other processes on the same CPU, and this seems like it might be the assumption that's broken by the DMP...

I'll have to read more, I've just skimmed the abstract and introduction so far.

[usrusr]

My attempt at skimming for "what would be needed": controlled input specifically designed to make the process with the keys speculatively fetch or not fetch address lookalikes depending on key bits, and some observer comparing timing either of fetches to canary addresses after the key has or has not triggered a fetch, or observing how the timing of the crypto parts changes with our without canary fetches beforehand. Or perhaps even outside observability from inputs that would either fetch the same canary address twice, or two separate address, depending on key bits?

In any case, the stack of "this could not possibly be workable / but with enough statistics it can, and computers are plenty fast to generate statistically useful case numbers" is truly mindboggling with these attack vectors.

[adrianN]

That usually just means that you need to collect more data to filter out the network noise.

[vbezhenar]

If you can collect enough data you can break any password just by trying.

"More data" might be not practical.

[eru]

Anything you execute on behalf of a user, even if the binaries are trusted, can effectively become untrusted code.

[pmontra]

So, CPUs or cores (and maybe RAM) dedicated to run only trusted and only untrusted code?

Examples (I'm running Debian)

The kernel, the X11 server, terminal, ssh, bash, anything coming from the official Debian repos including the password manager: in the trusted environment.

browsers, electron apps, anything installed from unofficial repos or language and package managers (npm, rvm, asdf, etc): in the untrusted environment.

It reminds me of mainframes and their redundant and compartmentalized hardware architecture.

[sofixa]

> terminal, ssh, bash

> X11 server

Those can very easily execute untrusted code.

[pmontra]

Yes, but it can be countered by pinning "random-script-from-the-internet.sh" to the untrusted environment. The fork/exec inside bash (or whatever bash is using now) should take care or that, or the kernel itself which is probably a better option. bash + ls -> trusted because ls is in some way marked as trusted, bash + random-script -> untrusted, possibly by default.

[PhilipRoman]

Well it makes no sense to worry about side channel attacks if you don't have isolation in the first place, so there is an implicit assumption that you have a sandboxing layer like VM/container/browser (or the built in unix user separation) which don't care about terminals or X11 (usually a separate X server is used which is running inside the sandbox context).

[JediPig]

the author(s) of the article, completely ignore the cpu itself can be patched. there is microcode underneath the ARM instructions for such scenarios. Look at intel, there has been undocumented microcode for decades I beleive these articles are just hype for street cred.

[eek2121]

From what I have read, the microcode on M-series chips is NOT updatable. If this is the case, tsk tsk Apple.

[not_the_fda]

I thought microcode was an artifact of CISC architectures, while the Arm is a RISC architecture.

[bhawks]

So you browse the Internet with JavaScript turned off? You're a bigger person than I am ;).

The risk here is that there are more individuals with the skills to take this type of attack and bring it to a browser near you.

One apps data is another apps code.

[pmontra]

I use uMatrix and allow first party JS. When some sites break I open the matrix look at what they would like to load and allow one more origin and reload. An example: chatgpt works by allowing JS from the first party domain, *azure.com and oaistatic.com, which looks like something from OpenAI. It would like to load JS from three other domains but it works even if I don't allow them, so there is no need to let that code run.

[rpdillon]

This is the way.

Unfortunately, I've had no luck getting others to buy into the idea that they should understand this level of detail so they can make these calls. Quite frustrating and depressing, since companies will relentlessly exploit their indifference.

[TheDong]

If other people buy into this idea, then every site will begin proxying third-party javascript.

If the only way to get trackers on the average person is to serve it from the same first-party domain, or to bundle it in with the giant 'app.js', you better believe they'll do that.

Right now, the fact that only a small fraction of people run adblockers, and an even smaller fraction block javascript, is what allows it to work.

[pmontra]

Not many developers do that. The general population won't even understand what they are looking at. If you are good at teaching you can give them an idea and a few of them maybe will do it, but the time invested in the allow/reload loop is probably too much unless one is really committed.

In my case when every attempt fails I know it could be the side effect of some other privacy add on. If it's a random blog/news, that's the end of it. If I really have to use that site I open Chrome, do what I have to do, close it. Of course given a choice I pick sites that work well with only JS from a few inevitable sources.

[PhilipRoman]

Indeed, the scary thing is that there is no theoretical limit to how sophisticated a side channel attack could be. Imagine all the timing data that could in theory be gathered from html layout engines and css, even without javascript, just by resource loading times.

I would like to salute my shitty ISP for keeping me safe from timing attacks using their unreliable network infrastructure.

[robin_reala]

This attack is now why browsers segment caching into a combination of requesting domain and asset URL, rather than just caching the asset on its own. It slows down for example Google Fonts, but means that a site can’t check to see that you’ve visited a competitor by timing an asset load from their site to see whether it’s in the cache.

[aaomidi]

The entire point of this chip is to keep secrets hidden from local processes.