GoFetch: New side-channel attack using data memory-dependent prefetchers

https://gofetch.fail

by kingsleyopara • 2 years ago

297 92 2 years ago

gofetch.fail

woadwarrior01• 2 years ago

Reminded me of the Augury attack[1] from 2022, which also exploits the DMP prefetcher on Apple Silicon CPUs.

[1] https://www.prefetchers.info

loeg• 2 years ago

Yes, they specifically mention that in the article and FAQ.

Findecanor• 2 years ago

BTW. Three of the authors of GoFetch where also behind Augury.

martinky242• 2 years ago

Why does every attack needs its own branding, marketing page, etc...? Genuine question.

xena• 2 years ago

So people talk about it

sapiogram• 2 years ago

Well, names are useful for the same reason people's names are useful. The rest just kinda happens naturally, I think.

yborg• 2 years ago

Yes, it saves time vs. starting a discussion on "that crypto cache sidechannel attack that one team in China found".

martinky242• 2 years ago

Name makes enough sense. "Branding, marketing page, etc..." was my question.

"Happens naturally" isn't really an answer.

fruktmix• 2 years ago

It's science these days. They need funding, one way is to get people to recognize the importance of their work

modeless• 2 years ago

Science isn't just about discovering information. Dissemination is critical. Communicating ideas is just as important as discovering them and promotion is part of effective communication. It's natural and healthy for researchers to promote their ideas.

FiloSottile4• 2 years ago

Names are critical to enable discussion.

The "marketing" page is where documentation is. Summaries that don't require reading a whole academic papers are a good thing, and they are the place where all the different links are collected. Same reason software has READMEs.

Logos... are cute and take 10-60 minutes? If you spend months on some research might as well take the satisfaction of giving it a cute logo, why not.

saagarjha12• 2 years ago

Why does the comments of every such attack need a question about why it has its own branding, marketing page, etc…? Genuine question.

(Seriously, this comes up every time, just do a search for it if you actually want to figure out why.)

0xedd2• 2 years ago

Because it makes it feel like you need some marketing department if you want to publish your work. Rather than give _only_ the work merit, we give too much merit to its colorful presentation. That shouldn't be the case.

12_throw_away• 2 years ago

Dunno, but I'm glad they do it. In other fields of research, researchers often purposely hold off on naming something, so that the community kind of has no choice but to name it after the authors themselves.

Eg in my field, they would have called Spectre "the Horn-Genkin-Hamburg vulnerability" or something. Which one of these is hard-to-remember jargon, and which one is catchy and evocative?

jerf• 2 years ago

As long as we're getting efficiency cores and such, maybe we need some "crypto cores" added to modern architectures, that make promises specifically related to constant time algorithms like this and promise not to prefetch, branch predict, etc. Sort of like the Itanium, but confined to a "crypto processor". Given how many features these things wouldn't have, they wouldn't be much silicon for the cores themselves, in principle.

This is the sort of thing that would metaphorically drive me to drink if I were implementing crypto code. It's an uphill battle at the best of times, but even if I finally get it all right, there's dozens of processor features both current and future ready to blow my code up at any time.

FiloSottile4• 2 years ago

Speaking as a cryptography implementer, yes, these drive us up the wall.

However, crypto coprocessors would be a tremendously disruptive solution: we'd need to build mountains of scaffolding to allow switching to and off these cores, and to share memory with them, etc.

Even more critically, you can't just move the RSA multiplication to those cores and call it a day. The key is probably parsed from somewhere, right? Does the parser need to run on a crypto core? What if it comes over the network? And if you even manage to protect all the keys, what if a CPU side channel leaks the message you encrypted? Are you ok with it just because it's not a key? The only reason we don't see these attacks against non-crypto code is that finding targets is very application specific, while in crypto libraries everyone can agree leaking a key is bad.

No, processor designers "just" need to stop violating assumptions, or at least talk to us before doing it.

bee_rider9• 2 years ago

I don’t think the security community is also going to become experts in chip design, these are two full skill sets that are already very difficult to obtain.

We must stop running untrustworthy code on modern full-performance chips.

The feedback loop that powers everything is: faster chips allow better engineering and science, creating faster chips. We’re not inserting the security community into that loop and slowing things down just so people can download random programs onto their computers and run them at random. That’s just a stupid thing to do, there’s no way to make it safe, and there never will be.

I mean we’re talking about prefetching. If there was a way to give ram cache-like latencies why wouldn’t the hardware folks already have done it?

saagarjha12• 2 years ago

Processor designers are very unlikely to do that for you, because everyone not working on constant time crypto gives them a whole lot of money to keep doing this. The best you might get is a mode where the set of assumptions they violate is reduced.

olliej7• 2 years ago

No, processor designers "just" need to stop violating assumptions, or at least talk to us before doing it.

No, you don't get to say processor designers need to stop violating your assumptions. You need to stop making assumptions about behaviour if that behavior is important (for cryptographic or other reasons). Your assumptions being faulty are not a valid justification, because that would mean no one could have ever added any caches or predictors at any point because that would be "violating your assumptions". Also lets be real here: even if "not violating your assumptions" was a reasonable position to take, it is not reasonable in any way to make any kind of assumption about modern processors (<30 years old) processors not caching, predicting, buffering, or speculating anything.

If you care about constant time behaviour you should either be writing your code such that it is timing agnostic, or you could read the platform documentation rather than making assumptions. The apple documentation tells you how to actually get constant time behavior, rather than making assumptions.

eximius• 2 years ago

Wouldn't that "just" allow someone to see if a key was present (and any information that informs) but dramatically help prevent secret key extraction?

heresie-dabord• 2 years ago

processor designers "just" need to stop violating assumptions

"Security" rarely (almost never) seems to be part of any commercially-significant spec.

Almost as if by design...

gabrielhidasy• 2 years ago

Many modern architectures have crypto extensions, usually to accelerate a few common algorithms, maybe it would be good to add a few crypto-primitives instructions to allow new algorithms?

sargun• 2 years ago

I think what's more likely is "mode switching" in which you can disable these components of the CPU for a certain section of executing code (the abstraction would probably be at the thread level).

bee_rider9• 2 years ago

One option would be for people to stop downloading viruses and then running them.

SpaghettiCthulu• 2 years ago

Except when these vulnerabilities are exploitable from JavaScript in your web browser.

Joel_Mckay• 2 years ago

Encrypted bus mmu have existed since the 1990's.

However, the trend to consumer-grade hardware for cost-optimized cloud architecture ate the CPU market.

Thus, the only real choice now is consumer CPUs even in scaled applications.

Kluggy• 2 years ago

Isn't that the entire point of the secure enclave[1]?

https://support.apple.com/guide/security/secure-enclave-sec5...

john_alan3• 2 years ago

If you look at the cryptokit API docs the Secure Enclave essentially only supports P-256. Which is maybe why they didn’t include ECC crypto in the examples.

lxgr3• 2 years ago

The secure enclave is not a general-purpose/user-programmable processor. It only runs Apple-signed code, and access is only exposed via the Keychain APIs, which only support a very limited set of cryptographic operations.

Presumably latency for any operation is also many orders of magnitude higher than in-thread crypto, so that just doesn't work for many applications.

a-dub• 2 years ago

see DIT and DOIT flags referenced in the paper and in the faq question about mitigations. newer CPUs apparently provide functions to do just that.

theobservor• 2 years ago

The end result of these side channel attacks would be to have CPUs that perform no optimizations at all and all opcodes would run in the same number of cycles in all situations. But that will never happen. No one wants a slow CPU.

As long as these effects cannot be exploited remotely, it's not a concern. Of course multi-tenant cloud-based virtualization would be a no go.

bee_rider9• 2 years ago

We need to drop all the untrusted code on some horrible in-order, no speculative execution, no prefetching, 5 stage pipeline from architectures 101 class core.

graemep• 2 years ago

It might be preferable.

We have ridiculously fast hardware. In many use cases (client machines in particular) we do not usually really need that. I would gladly drop features for security.

wmf• 2 years ago

If untrusted code includes JavaScript that would make Web apps ridiculously slow. (I know what you're thinking...)

_factor• 2 years ago

This is why high core counts and isolation matter. Isolate the code to a specific core. Assuming everything is working as intended, an exploit won’t compromise other tenants.

lenerdenator• 2 years ago

multi-tenant cloud-based virtualization

And that's why I'm not as worried about this as I was about the same vulnerability in Intel chips a few years ago.

There are a few cloud service providers that will rent you clock cycles on a rack-mounted Mac Mini, but not many, and even then they're for highly-specific workloads or build tasks. I suppose that's a problem for people paying far out the butt for that kind of service, but the vast majority of Apple Silicon devices are never, ever going to host cloud services.

xiconfjs• 2 years ago

From the paper: "OpenSSL reported that local side-channel attacks (...) fall outside of their threat model. The Go Crypto team considers this attack to be low severity".

lxgr3• 2 years ago

At least one Go crypto developer publicly expressed concern about this very issue in 2021: https://github.com/golang/go/issues/49702

john_alan3• 2 years ago

On reading it seems a lib like libsodium can simply set the disable bit prior to cryptographic operations that are sensitive on M3 and above.

Also looks like they need to predetermine aspects of the key.

Very cool but I don’t think it looks particularly practical.

saagarjha12• 2 years ago

Can the DMP be disabled?
Yes, but only on some processors. We observe that the DIT bit set on m3 CPUs effectively disables the DMP. This is not the case for the m1 and m2.

Surely there is a chicken bit somewhere to do this?

john_alan3• 2 years ago

I’ve often wondering how are these bits set?

Like can you do it from Swift? Or need assembly?

saagarjha12• 2 years ago

It's probably in a MSR accessible from the kernel?

Shtirlic• 2 years ago

Is it naive to ask whether implementing this mitigation would impact performance and memory interaction speed?

d-z-m• 2 years ago

what's the attack vector here? access to an encrypt oracle and co-location on the target machine?

0xedd2• 2 years ago

Why does Apple have so many hardware backd... innocent bugs?

olliej7• 2 years ago

why do we even need caches?

why do we need prefetchers?

But in answer to your bullshit backdoor conspiracy theory (JFC processors have caches and timing variants because people want fast CPUs, you cannot have constant time and fast, apple is not the only company with prefetchers), here's some apple provided documentation on how disable the hardware backd... enable constant time operations specifically for the purpose of cryptography, almost like it's designed into the hardware. So weird. https://developer.apple.com/documentation/xcode/writing-arm6...

howinteresting2• 2 years ago

The M1 and M2 don't have that bit.

m0rshu• 2 years ago

Same reason Intel and AMD had Meltdown and Specter.

olliej7• 2 years ago

If you're writing cryptographic routines you should either use the platform cryptography libraries, or follow the documentation:

https://developer.apple.com/documentation/xcode/writing-arm6...

slowmovintarget• 2 years ago

So malware scanning and virus scanners just became relevant for Macs and IPads.

(Compromise must be running on the same hardware.)

GoFetch: New side-channel attack using data memory-dependent prefetchers

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