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Tim Sweeney has a point about Fortnite EAC support

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One of the big topics of discourse in the Linux gaming sphere recently has been Tim Sweeney's statement on porting Fortnite to the Steam Deck, where Sweeney argues that Linux would be too difficult of a target and the market not big enough to warrant the amount of resources it would take to bring all of Fortnite on the platform.

The central crux of the issue, from Sweeney's point of view, is that making Easy Anti-Cheat, with all of its capabilities, run on Steam Deck (and thus on Linux) would be extremely difficult. He argues, that for a game of Fortnite's size this would open the flood-gates to significant influx of cheaters.

There have been some responses to this from the Linux side, with some accusing Sweeney of exaggerating the difficulty of such a port or that his statements are conflicting, because he simultaneously believes the Linux market is too small to be worthwhile but also would provide a way for too many cheaters. I will address some of these aspects a bit later, but for now let's focus on the main technical blocker, which is Easy Anti-Cheat.

Easy Anti-Cheat, or EAC, is an anti-cheat solution which apparently comes in a few configurations. We know that it can be run in a configuration where it is compatible with Linux/Proton apparently with just a relatively simple toggle. However, this mode of operation is seemingly a comparatively high-trust configuration, where only part of the anti-tampering protections of EAC are active. This may prevent some cheats but fail to detect others, which can be perfectly reasonable for games, where the number of cheaters and potential cheaters are fairly low or other systems complement the anti-cheat solution. There are plenty of games, even some popular free-to-play titles, which at best have this level of anti-tamper protection and they don't seem to have a major cheating epidemic, so clearly in many cases this should be enough. We also don't know the scope of cheats that are detected by EAC in this configuration, so this system by itself may already be fairly comprehensive.

EAC also contains a kernel-level component, which on Windows is installed as a kernel driver. This allows EAC code to run at a very privileged level and inspect essentially any and all parts of the system in order to detect tampering. This provides a very broad level of monitoring, which is also harder to bypass. Based on Sweeney's comments, this is the mode of operation used by Fortnite. It is also a mode of operation that is technically incompatible with the Linux way of doing things.

In Linux, the standard way of delivering drivers is by submitting the driver into the kernel source code tree, which naturally requires that the driver be open source. Most drivers are delivered this way, where the driver gets tightly integrated into the kernel and the drivers are updated when the kernel is updated. There are of course some notable exceptions to this rule, the largest of which is the Nvidia driver. The Nvidia driver is instead loaded as a separate kernel module, which allows Nvidia to keep its source code hidden, but also allows the driver to be updated separately from the kernel. So, EAC could surely use this approach as well, right?

The separate kernel module approach comes with some gotchas. Firstly, the kernel is licensed under GPLv2 and many of the parts in the kernel require the calling code to also be GPLv2 due to the "viral" quality of GPL. This means that, legally speaking, if Epic were to turn EAC into a kernel module and started poking around the kernel APIs, they'd have to open source EAC or they'd be in a legal grey area. The first approach is obviously not possible due to their business model and the second is at least not a great look.

Another problem with separate kernel modules is that the Linux kernel only guarantees a stable user-facing interface. This means that almost anything is allowed to change inside the kernel as long as user-level programs continue functioning. This is also the reason why sometimes the Nvidia driver stops working when you upgrade from one kernel to the next without installing an up-to-date Nvidia driver as well. So, when Sweeney is complaining about the multitude of kernel configurations, he's not wrong. EAC would need to maintain a compatibility shim similar to that of the Nvidia driver, which ensures that the EAC kernel module functions with each kernel version out there. Every time the kernel updates, an EAC engineer would need to go over the changes and update the compatibility shim every time there's a breaking change while still maintaining the compatibility with older kernel versions.

Theoretically you could overcome this problem somewhat by only targeting the Steam Deck and its SteamOS. This would give you a single kernel version to target, although Epic would need to negotiate with Valve in order to ensure their driver is somehow shipped with SteamOS.

But the problems don't end there. Since Linux is a fully open platform, there is technically nothing that would prevent a determined cheater from cracking open the Linux source code and making some tactical changes to how the kernel behaves, building the kernel and then making the EAC kernel module blind. On Windows the EAC developers can assume that the black box that is the NT kernel is at least somewhat difficult to modify by users. This means that in kernel-space they can assume some level of security through obscurity. On Linux this assumption does not hold. The only way for Epic to overcome that problem would be to negotiate with Valve to lock down the Steam Deck, which Valve has already decided not to do.

So, from EAC's point of view the Linux platform can never be quite fully trusted, which is entirely fair, because from the user's point of view EAC can never be quite fully trusted.

But surely Epic could still somehow bring Fortnite to the Steam Deck, right? Surely they could ship a version of Fortnite without the kernel-level component, right?

That they could, which brings us to the points about market share and the viability of cheating. Sweeney argues that the Linux market is too small, which initially sounds a bit odd because he then goes on to worry about the large numbers of cheaters. The kicker is here that the small Linux market doesn't necessarily guarantee a low number of cheaters. If it turns out that certain cheats are possible via a Linux version of Fortnite, this will attract some cheaters to use the platform in order to bypass EAC. It won't be all of the cheaters, many casual cheaters would likely not bother to learn Linux in order to cheat in a video game, but there is no doubt a group of cheaters that would take the opportunity. So, Fortnite would see some increase in cheating, but without good data it is hard to determine how big that effect would be. However, considering the popularity and free-to-play nature of Fortnite, it could very well be that it would be an attractive enough target for cheaters to attack even if there is a slightly higher initial investment. Cheat makers on the other hand would probably eventually find ways to package their offerings in an accessible enough format, like boot-to-cheat USBs or pre-configured VM images.

Some solutions to this problem have been proposed. For example, they could silo Steam Deck/Linux users in such a way that they will never come into contact with the rest of the playerbase. This would contain cheating, but it's also a hard-handed measure that would likely be unpopular. It would also require some amount of work to accomplish and I think it's fair for Epic to discount options that would cause extra work on them.

So, what's the solution to the problem? Here's the thing: I don't think there is one. My personal opinion is that client-side anti-cheat is fundamentally limited and taking it into the kernel is a bandaid that comes with excessive cost and is simply incompatible with the Linux platform. So, as long as Epic insists on maintaining its current anti-cheat approach with Fortnite, I just don't think there's going to be Fortnite on Linux.

And that doesn't mean Tim Sweeney is wrong or lying about the difficulties of adapting that approach to Linux. It just means that a new or different approach is needed in the future.

Article taken from GamingOnLinux.com.
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I'm a Linux gamer from Finland. I like reading, long walks on the beach, dying repeatedly in roguelikes and ripping and tearing in FPS games. I also sometimes write code and sometimes that includes hobbyist game development.
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148 comments
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F.Ultra 17 Feb
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Quoting: EagleDelta
Quoting: Koopacabraswhat I don't get about this whole article... is how does the heck Fortnite for Android works? and I think there's enough android "distros" out there, that have plenty of different kernels. Did google let them run a proprietary module on their kernels?
I'm sorry if my question is too stupid I simply ignore this.

They will detect if you are running with root, or running with an unlocked bootloader, or try to see if you're running a custom ROM and block those things.

All of which could be completely be worked around by creating a forked kernel in the very way that Tim says will definitely happen on the deck or Linux even though it so far haven't happened on Android which have a userbase that is several orders of magnitude larger than either the Deck or Linux native.
F.Ultra 17 Feb
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Quoting: 14I once scored too high on a WPM typing test. In order to save my score, I had to achieve it again in a different session with various text. That was super annoying!

Something like that could work for players who get automatically flagged or voted as possibly cheating. Modern, multiplayer shooters have some pretty detailed player statistics. You could use those, maybe add player's camera angle and how much of the target's hit box was even visible, to form an algorithm to detect anomalies.

Sure takes the fun out of game development, huh? Well, it could still be handled by a 3rd party in the form of licensed software you package into the game or your game servers and feed its API data from your game. It's all behind the scenes to the player and will work on any operating system that the game's engine works. The game dev has to put some effort into implementation but doesn't have to "recreate the wheel" every new game.

Or here's a thought. Use all that statistics to flag potential cheaters and then have moderators connecting to the server<->client stream of such a flagged user and see what they should see and how they play and thus be able to detect if they can hit people behind walls and so forth. It's common on esports games to be able to switch to the players view so why not on any other highly competitive game.
marcus 17 Feb
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Quoting: HoolyDoesn't matter, the private key has to get there somehow. And how would you verify server-side that the client uses a specific individual TPM? The client could just lie to the server and then reroute the attestation request again.

The private key is generated by the TPM and never leaves it. The public key transmitted to the server for encryption is signed with the private key from the TPM vendor and thus cannot be "spoofed". The server knows all "known good" TPM vendors and their (public) signing keys.

Quoting: HoolyIf your security model involves placing trust onto the client in any shape or form, then it is deeply flawed, period.

Then FPS are basically impossible to make cheat proof. You *need* to trust the client to actually render walls ...
lets not forget that EAC used to work on linux natively prior to Epic buying it.
Cyba.Cowboy 22 Feb
Quoting: catbox_fuguelets not forget that EAC used to work on linux natively prior to Epic buying it.

I've not heard this before, but if true, it's not a good look for Epic Games... I suspect though, that they'll try and downplay this fact, so that people don't point out the hypocrisy of refusing to support Linux-based operating systems.
Mal 22 Feb
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Quoting: Cyba.Cowboy
Quoting: catbox_fuguelets not forget that EAC used to work on linux natively prior to Epic buying it.

I've not heard this before, but if true, it's not a good look for Epic Games... I suspect though, that they'll try and downplay this fact, so that people don't point out the hypocrisy of refusing to support Linux-based operating systems.

link to article

Officially it was announced as a "paused support". But I believe everyone here should be educated enough to understand corporate language.

BTW, since I start to get lost here... linux remains unsupported pausesupported correct? What we are disccussing here is just the official partial/non intrusive EAC 4 windows support for proton. Or is partial support also for linux native?
Cyba.Cowboy 22 Feb
Quoting: MalBTW, since I start to get lost here... linux remains unsupported pausesupported correct? What we are disccussing here is just the official partial/non intrusive EAC 4 windows support for proton. Or is partial support also for linux native?

EAC now has native support for Linux-based operating systems (again?); don't quote me, but I believe this applies only to the most recent version of EAC... However, Epic Games has publicly stated that they will not support a version of 'Fortnite: Battle Royale' (which uses EAC) for Linux-based operating systems at this time, either natively or via Proton.

This thread is about the reasoning behind that, as there is debate as to whether Epic Games' arguments in support of this stance are justified or not.


Last edited by Cyba.Cowboy on 22 February 2022 at 8:40 pm UTC
Hooly 25 Feb
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Quoting: marcus
Quoting: HoolyDoesn't matter, the private key has to get there somehow. And how would you verify server-side that the client uses a specific individual TPM? The client could just lie to the server and then reroute the attestation request again.

The private key is generated by the TPM and never leaves it. The public key transmitted to the server for encryption is signed with the private key from the TPM vendor and thus cannot be "spoofed". The server knows all "known good" TPM vendors and their (public) signing keys.

Quoting: HoolyIf your security model involves placing trust onto the client in any shape or form, then it is deeply flawed, period.

Then FPS are basically impossible to make cheat proof. You *need* to trust the client to actually render walls ...
You can still redirect the original signing request, how would the server know which TPM resides on which machine?

Yes, FPS are impossible to prevent against cheaters, but that's nothing new.
Detecting cheaters and banning them later however, can be done on the server-side just fine.
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