How the Nintendo Switch prevents downgrades by irreparably blowing its own fuses

https://blog.jonlu.ca/posts/nintendo-switch?ref=hn

by jonluca • 6 years ago

136 107 6 years ago

blog.jonlu.ca

camgunz2• 6 years ago

Are these fuses extremely small? I would assume they’re easy to bypass otherwise.

wutbrodo• 6 years ago

From the beginning of the article:

It’s theoretically possible to physically modify the SoC and replace the fuses, but it’s so prohibitively invasive and expensive that it’s not a real option.

camgunz2• 6 years ago

Yeah I read that but, I wanted to know why.

mlyle2• 6 years ago

They are produced by lithography and are on the actual die of the system-on-chip that contains the processor. I believe they're IBM's eFUSE technology on Tegra, but antifuses have been used for similar purposes:

https://www.semanticscholar.org/paper/IBM-System-z9-eFUSE-ap...

mmglr• 6 years ago

A few questions:

1. What was the intended use case behind the Tegra having 32 blowable fuses? Did Nvidia intend for those fuses to be used in this manner?

2. What is a non-retail switch?

mlyle2• 6 years ago

Fuses and OTP are a very common thing to throw in to systems. Most microcontrollers offer capabilities like this, and now they're drifting into more general purpose, larger SOCs. Maybe you use it to keep a serial number, or to separate product families, or for something like this.

Tegra's main purpose of the fuses is to handle holding cryptographic keys, boot parameters, and to disable the debug port. But since they have a fuse unit already, they provide a few words for the end-user to use as they please.

I too am curious what "non-retail" means in this context.

sirn• 6 years ago

I too am curious what "non-retail" means in this context.

Maybe dev kits? AFAIK Switch has at least two dev kits (SDEV/EDEV) for different purposes so it kinda makes sense to call them non-retail.

Luuseens• 6 years ago

"non-retail" are usually either devkits, or units used for demo stands in shops.

izacus• 6 years ago

1. Most likely - Switch isn't the first console which used fuses like this. Xbox 360 had them as well.

henrikeh• 6 years ago

One common use case of the fuses is to prevent attack vectors which downgrade software to a vulnerable version. Using the OTP fuses older versions can be prevented from running to some extend.

pjc502• 6 years ago

Lots of system-on-chip devices have an array of fuses. Usually there's one for "permanently turn off JTAG" after factory testing, and most of the rest will be user-defined. Other uses include embedding serial numbers and cryptographic keys.

dvhh• 6 years ago

This was already in use in other game system (for example the xbox 360, see https://en.wikipedia.org/wiki/IBM_eFUSE )

felipelemos• 6 years ago

The article explicit says that on the very first paragraph.

CodeArtisan• 6 years ago

Also in use in Samsung smartphones: https://en.wikipedia.org/wiki/Samsung_Knox#e-fuse

Mindwipe• 6 years ago

Lots of embedded devices really. Pretty much all satellite/cable set top boxes too.

slim• 6 years ago

It backfires like this : users are trained to never upgrade. Games that target a specific version lose sales.

syspec• 6 years ago

In practice users don't even know what version they're on

daveFNbuck• 6 years ago

I don't think this applies to consoles like the Switch. I don't think the average user ever feels the need to revert to an earlier firmware version, and games don't target particular firmware versions. They tend to just work.

ElCapitanMarkla• 6 years ago

How many people running CFW are buying games though?

jowsie• 6 years ago

We do exist!

hrktb3• 6 years ago

As a user, I feel Nintendo has been pretty good about updates: they don't update a lot, and each updates has user facing features with QOL improvements.

It's not in the same situation as iOS updates that were effectively slowing down the devices or Windows Update that don't seem to the user to bring anything.

FakeRemore3• 6 years ago

each updates has user facing features with QOL improvements

You must be joking. The meme about "stability intensifies" with Switch updates isn't just a joke. Most of their updates are minor bugfixes and "increasing stability" (fixing exploits). They're far more interested in fixing exploits than they ever were in improving the OS in any meaningful way for the user. It's been 3 years and the only major QOL change I see on that list is making the all software page not useless.

https://en.wikipedia.org/wiki/Nintendo_Switch_system_softwar...

hd43• 6 years ago

There is an easy workaround developed by the Switch homebrew community, simply upgrade from within a custom firmware (such as Atmosphere-NX) and run a tool called ChoiDuJourNX which bypasses the fuse-burning.

If you're careful you can keep a backup trail going all the way back to your original device firmware and restore/downgrade it using the Hekate system tool. It has already been pointed out that there isn't much reason to do this, AFAIK the main reason people either held out on older firmwares or kept up a backup trail to them was in order to take advantage of possible firmware-version-specific exploits, the gold standard being a coldboot exploit.

rekoil2• 6 years ago

And for those who stayed on the 4.1.0 fuseset (or certain versions below that) there are warmboot exploits available. So those who are able to "normally" boot those firmwares do not need to use AutoRCM (or an RCM-"jig") to access RCM anymore.

hd43• 6 years ago

While this is true, I was essentially saying that you don't have to remain on an older firmware as long as you're careful about how you move around between versions. I'm on 10.0 but I could go back to 3.1.0 anytime, and then move somewhere in between those versions if we got a coldboot exploit for example (which according to notable members of the Switch homebrew community is not likely).

roblabla2• 6 years ago

The reason this "easy workaround" works at all is that there is a BootROM exploit that trivially allows running arbitrary code in the BootROM. This allows us to run our own bootloader instead of Nintendo's, bypassing their fuse burning logic. Had Nvidia not fucked up their USB implementation (along with other part of their platform), this would have been harder to bypass.

[0] https://www.reddit.com/r/SwitchHacks/comments/7rq0cu/jamais_...

artsyca2• 6 years ago

I don't want to sound like I'm pontificating or defecating on the corporacy at everyone's favorite hardware company but it strikes me that these sorts of lapses are cultural and stem from this tedious emphasis everyone places on having "relaxed working environments"[0]

Does it surprise you that the product of this culture also has relaxed security characteristics?

[0] https://www.nvidia.com/en-us/about-nvidia/culture-at-nvidia/

outadoc2• 6 years ago

I'm unclear on how these hardware fuses actually work. Are they actual fuses that can be burnt on will by excessive power?

When the article says:

The boot loader verifies a specific fuse, FUSE_RESERVED_ODM7, to prevent downgrading. Each software version expects a different number of fuses to be blown [...]

Does this mean FUSE_RESERVED_ODM7 actually contains multiple fuses?

ThePowerOfFuet• 6 years ago

I'm unclear on how these hardware fuses actually work. Are they actual fuses that can be burnt on will by excessive power?

No, they're not like the fuses in your house. These can be blown by software to irrevocably change something which can then be verified later, or in other cases to prevent reprogramming of a microcontroller (which can be programmed only if the programming fuse is still intact.

Does this mean FUSE_RESERVED_ODM7 actually contains multiple fuses?

No, that's the name of one fuse. Once you upgrade the device next time, the upgrade tool would, for example, blow FUSE_RESERVED_ODM8; older software would verify that this fuse (and the higher-numbered ones) are NOT blown, and refuse to boot otherwise.

outadoc2• 6 years ago

Thanks! Definitely more clear.

arghwhat2• 6 years ago

No, that's the name of one fuse.

No, it's a 32-bit segment belonging to the 256-bit odm_reserved segment. FUSE_RESERVED_ODM7 is specifically the last 32-bit segment.

Some fuse information can be read here: https://docs.nvidia.com/jetson/archives/l4t-archived/l4t-323....

arghwhat2• 6 years ago

"Fuses" in this context are just non-volatile memory that cannot be reset. Once a bit is set to 1, it stays there. They're often used for configuration and for things like sealing off programming/readout on microcontrollers.

FUSE_RESERVED_ODM7 is 32 bits wide, hence contains "32 fuses". The system has many fuses, but 256 bits (RESERVED_ODM0-RESERVED_ODM7) are for the device manufacturers to use for their own purpose, which is what Nintendo is doing here.

londons_explore2• 6 years ago

On some chips they are literally bits of polysilicon that burn. On most devices they're flash memory that doesn't have any circuitry to do erases.

pjc502• 6 years ago

They are the same concept, yes, but implemented in silicon; this short paper shows how it works with diagrams and a microscope photo. https://people.maths.ox.ac.uk/fowler/papers/2010.6.pdf

m101• 6 years ago

Why do they bother with this if someone is going to make a software workaround? Seems like people who would look to downgrade firmware might also be the same that would be able to implement the workaround.

hd43• 6 years ago

Apathy. The vast majority of consumers won't bother. Also, the Switch's security was actually comparatively solid. It was a flaw in the Tegra X1 (thanks Nvidia!) component that led to an exploit being discovered.

wolfgke• 6 years ago

There are 256 bits in the set of ODM_RESERVED fuses, and there are 8 ODM_RESERVED. This allows for 32 fuses, or 32 future FW versions (provided they burn a fuse on every major release).

Can someone explain how the author gets from the numbers 256 and 8 to the count of 32 fuses?

nitrogen• 6 years ago

Maybe that's 256 bits divided into eight chunks of 32?

indigo945• 6 years ago

I think it's the other way around, there's 32 fuse-bytes of 8 fuse-bits each, adding up to 256 bits of PROM.

marcan_424• 6 years ago

Fuses are in 32 bit words. There are 8 such words available for ODM usage, giving a total of 256 fuse bits. However, of those only one word is used for the anti-downgrade stuff. So that's just 32 firmware levels.

adrr• 6 years ago

What happens if some hacker finds a remote exploit and starts blowing all the fuses on people's devices?

Maxious• 6 years ago

Local exploits are popular anyway, trick people into downloading the latest game which just wipes out the operating system https://www.nintendolife.com/news/2018/07/fake_nintendo_swit...

londons_explore2• 6 years ago

If this was widespread, Nintendo would just release a firmware without fuse checks.

roblabla2• 6 years ago

More like, they'd just release a firmware without the remote exploit in the first place. The consoles that got their fuses wiped would be bricked anyways, you wouldn't be able to install the firmware without fuse-checks on it through normal methods (Nintendo, however, could replace them easily).

kiplkipl2• 6 years ago

Then they can already brick your device by replacing the firmware.

This is the reason for threat models. Don't waste your time worrying about theoretical but redundant attacks.

m-p-3• 6 years ago

A massive recall and a world of hurt for Nintendo and Nvidia

unnouinceput• 6 years ago

Nintendo switch emulator. Game over.

classics2• 6 years ago

Clickbait title.

monadic23• 6 years ago

Shameful, honestly.

bibabaloo3• 6 years ago

I'm curious, how do Nintendo justify such an anti-consumer protection? It seems like it only really has upside for them.

orloffm• 6 years ago

Justify to whom? I am a consumer and this is irrelevant to me. And Nintendo has always been aggressively fighting emulation/homebrew, so it is nothing new.

Jonnax• 6 years ago

They sell the machine as a single purpose box that plays games sold by them in their store.

If someone buys it expecting something different that's really on them.

manojlds• 6 years ago

Why is the upside only to Nintendo? If Nintendo can maintain a proper "hack free" device more third parties will be willing to release their games on the Switch - as a consumer my upside is that I get the games.

bibabaloo3• 6 years ago

Huh, that's a really nice way of looking at it. I suppose I was thinking that it's my device that I've paid for so there shouldn't have unnecessary restrictions imposed on it. But it's true that I'd prefer a restricted device with a greater game library over an unrestricted device with no games!

monadic23• 6 years ago

How do you figure? You could also argue this restricts the switch market by only allowing capital-infused creators.

tasogare2• 6 years ago

This is not anti-consumer as consumers don’t care, nor running homebrew or pirated games are supported or advertised features. This is something that target precisely people who doesn’t want to be consumer: those that want to get and play games for free. Now, there is also the very very minor homebrew community, which should buy a devkit instead if running code is their main goal.

marcan_424• 6 years ago

Devkits are not available to the general public, only to licensed developers who signed NDAs, and are severely restricted in how they can distribute their software.

syshum• 6 years ago

>This is not anti-consumer as consumers don’t care

consumers "caring" about something is not the definition of Anti-Consumer at all, there are all manner of business practices that have been made illegal because they were anti-consumer that the majority of consumers did not care about (and still do not). For example the Warranty if Removed Stickers on electronics. Most consumers do not care if the manufacturers place them on devices however this practice is very much Anti-Consumer and is illegal in the US

> This is something that target precisely people who doesn’t want to be consumer: those that want to get and play games for free.

Ahh yes, If I want complete control over my device, what to use my device in a non-standard way, or some other reason I do not want a manufacturer to permanently alter my device with a firmware change it must mean I only oppose it because I want free games...

I also oppose the war on drugs, do i only do that because I want to get high as well? or is it a fundamental ethical reason around property ownership and the role of manufacturers as SELLERS not leasing agents of a device

Wowfunhappy• 6 years ago

Is this any different from Apple with the iPhone?

The iPhone bothers me much more because it's a general-purpose computer.

_sbrk• 6 years ago

No, it's not and has never been held out as such. iPhones are a captive market. If you bought one, you bought into the closed ecosystem. Be that for convenience or ignorance, you are now subject to the whims of Apple.

Android is another path, but perhaps just as capitalistic as Apple, but by different mechanisms.

You are always free to buy raw hardware and build your own phone from scratch, and write all the software for it.

Life is a series of compromises. Choose wisely.

nottorp5• 6 years ago

As far as i know Nintendo is the only console maker still having region locks and being extremely fussy about transferring your purchases when your hardware dies/is replaced.

I'd call THAT anti consumer.

Correct me if i'm wrong, but that's the impression I got from reading here and there and the reason I don't own Nintendo products.

currymj• 6 years ago

Nintendo’s portable systems (going back to the Game Boy and including the Switch) have never had region locks, on the logic that somebody might want to buy a new game while traveling. The consoles (except for Switch) do, though.

mttjj2• 6 years ago

The Nintendo Switch is not region locked. You can play any game from any region on it.

Moving to new hardware is more complicated than it needs to be but is not restrictive.

Hamuko2• 6 years ago

I've had Japanese and European cartridges in my Switch without issues. (Haven't tried American cartridges yet despite owning four.)

koonsolo• 6 years ago

On a side note: a product is always a 2 party deal, and needs to be win/win.

For example increasing the price is always anti-consumer, but it might be part of the deal.

So I don't like to look at products from the perspective of 1 party, since it is always a negotiation between 2 parties where both end up with a win.

kiplkipl2• 6 years ago

The switch is 3 years old and - as the other comments have noted - this technique is much older. Yet, on a website for self-styled hackers, so many are learning about it for the first time. Did people really care that much?

If the device depends on write-once ROM that was written in the factory, is that also anti-consumer?

anoncake• 6 years ago

If the device depends on write-once ROM that was written in the factory, is that also anti-consumer?

That depends on the intent.

stordoff3• 6 years ago

I don't think it's quite as cut and dry as that. In some sense, the restrictions _enhance_ THE thing I bought it for - playing a wide range of games. A platform where piracy is trivial is less attractive to some publishers, which may mean they don't release games there, or release later than on other platforms. If the largely theoretical benefits of a more open platform (I'm simply not interested in using the hardware for other purposes, whether I can or not) cause even modest damage to the range of games available, that's not a good trade off for me.

Sony[1] with the PSP claimed that:

There's a number of titles from American publishers that will be there, but are we getting full-line support? No. I'm not going to bullshit you on that.
A lot of the stuff that will be announced at E3 we're very excited about, because they are huge titles. And we also believe that there's a way that you will be able to, not stop, but slow down the piracy in the first 30 to 60 days from a tech perspective. [...] That's been the biggest problem, no question about it. It's become a very difficult proposition to be profitable, given the piracy right now.

Of course they're incentivised to portray piracy as damaging to the platform even if it isn't changing publisher decision making to any significant extent, but it's an argument that makes sense, and I find it difficult to believe that it wasn't dampening publisher enthusiasm to at least some extent.

In some ways, I'd like to see a phased path to openness, where say ten years down the line or when official support is dropped, some of the barriers are taken away (most platforms get there anyway due to third party efforts, and as Sony allude to above, _slowing_ piracy can be sufficient), even if only to aid game preservation and avoid games being forever tied to a particular physical hardware platform.

[1] Specifically, Sony Computer Entertainment America's then senior vice president of publisher relations, Rob Dyer - https://www.gamasutra.com/view/feature/133097/the_sony_situa...

lkjaero• 6 years ago

Maybe this is a dumb question, but can these fuses be blown by accident? Eg: too much power in the switch. How do they mitigate this?

How the Nintendo Switch prevents downgrades by irreparably blowing its own fuses

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