[Solved] Non root Xorg on AMD video cards

The Main Man · Last edited by The Main Man on Thu Apr 25, 2019 1:05 pm; edited 3 times in total

Is it possible ?

Ant P. · Watchman Joined: 18 Apr 2009 Posts: 6920

You need to give the X server process read/write access to your input/DRI devices, and it needs to not change VT at startup (that requires root). Some config tweaks required, but it's doable.

The Main Man · Posted: Wed Feb 06, 2019 7:55 am Post subject:

With Intel I had no issues, with AMD I got error, error was modesetting or something, can't remember.
I asked because Wiki mentions just nvidia and intel, plus it says that the article is outdated.
https://wiki.gentoo.org/wiki/Non_root_Xorg

I'll try again more thoroughly, I gave up on first try and error because I needed X asap.

Anon-E-moose · Posted: Wed Feb 06, 2019 10:52 am Post subject:

If you are using modesetting driver, no matter which card, non-suid X doesn't work.
The non-modesetting drivers will work and the wiki needs to be updated to reflect that.
Especially since everyone seems to be heading towards modesetting.
To do modesetting will require a library/kernel change, if I'm not mistaken.
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The Main Man · Posted: Wed Feb 06, 2019 1:21 pm Post subject:

Yeah, I tried again and it says that amdgpu KMS modesetting driver is enabled, that's the error.

Got new hardware and I used genkernel, it's probably enabled in initramfs, didn't have the time to manually configure kernel, hardware rather.
When I do I'll try it again, I guess it will work.
Thanks for the information.

Anon-E-moose · Posted: Wed Feb 06, 2019 2:09 pm Post subject:

The Main Man · Posted: Wed Feb 06, 2019 2:22 pm Post subject:

amdgpu

The Main Man · Posted: Wed Feb 06, 2019 3:56 pm Post subject:

I compiled kernel manually, it still loads modesetting driver

Anon-E-moose · Posted: Wed Feb 06, 2019 5:08 pm Post subject:

To get it not to use modesetting you would have to set (at least part of) xorg.conf for that driver.

The Main Man · Posted: Wed Feb 06, 2019 5:57 pm Post subject:

Well, I'm afraid that KMS is mandatory for AMDGPU
Long story short, to disable modesetting all that was needed was nomodesetting as kernel parameter.
However, xorg (with no suid) changed the error message and now saying something about how DRI needs something... (I know... should have noted that down but I'm tired)
And indeed modesetting wasn't loaded, which I was able to see visually too, but turns out AMDGPU doesn't work without it.
Arch Wiki says that it's mandatory, so I don't know.

I guess, maybe someone with AMDGPU and the desire to use Xorg with -suid can solve this.

@Anon-E-moose, big thanks for trying, maybe I'll try playing with this more in next few days, but for now I give up.

Anon-E-moose · Posted: Wed Feb 06, 2019 6:44 pm Post subject:

You do indeed need KMS in the kernel,

But modesetting in X is separate from KMS.

X can use either modesetting driver which you'll see with the loading modesetting module message or not.

You have to specifically tell it to use the amdgpu driver only using something like the xorg code that I posted earlier, otherwise it tries to use the modesetting driver, which in turn calls the amdgpu driver.

I know it's confusing and I wish they would quit using the same terms for different things.
I feel the same way when the kernel talks about DRM and then we hear about drm applied to movies/media.

Note: Again I haven't played with amdgpu and am going on what I know from the nouveau driver. I assume that amdgpu will work without modesetting module in Xorg.
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The Main Man · Posted: Wed Feb 06, 2019 7:17 pm Post subject:

Forgot to say that I prior to that already made xorg config file /etc/X11/xorg.conf.d/20-amdgpu.conf with this inside :

Anon-E-moose · Posted: Wed Feb 06, 2019 7:49 pm Post subject:

That xorg file you posted should work. It's similar to what I posted.

As long as the modesetting driver doesn't show up, then you might be able to run non-suid X, using what the wiki mentions.

Note: I added my user to these groups, video, input and tty

You might want to read https://forums.gentoo.org/viewtopic-t-1088682-start-50.html scroll down about 1/3 way to see a long post by me talking about modesetting.
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The Main Man · Posted: Thu Feb 07, 2019 9:58 am Post subject:

I'm in those groups, that's not the problem, error would be different, permission denied related.
I was using -suid for a very long time but on Intel.
But this one I don't understand, there's not much info about it.
You say that with modesetting no matter which card, -suid can't work.
More specifically KMS is different than card MS
I tried with disabling KMS as the kernel parameter, then startx reported different error, instead of "...modesetting is loaded...." I got "....DRI needs...." (paraphrasing both error messages)
When I added xorg config file and specified amdgpu driver to be loaded, then the other two (radeonsi and modesetting) drivers weren't loaded.
According to Arch Wiki KMS is mandatory
Now, you say that doesn't matter and the one that matters for -suid is the Xorg modesetting driver.
I'm not loading Xorg modesetting driver anymore since I added xorg config file.

I'll try again but I'm not optimistic about it at this point.

Edit:
actually I'm not in the tty group, wasn't needed for Intel btw, doubt it's any different for amdgpu, I think that part is ok, gpu driver is the problem.

Anon-E-moose · Posted: Thu Feb 07, 2019 10:49 am Post subject:

It just might not run as non root.

I played around with non root, but just went back to suid X, just the way I've been using it for many years. Non root is still too flaky, IMO.
What needs to be done is what bind and apache do, start as root and drop privileges that it doesn't need but that will require changes to at least the video drivers (as that's the basic holdup)
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Goverp · Veteran Joined: 07 Mar 2007 Posts: 1995

AFAIK Arch linux default is usermode X; I did a brief scan of their wiki article on AMDGPU and found no mention of problems. Their wiki article on Xorg has a section on "Rootless Xorg" that might point at relevant configuration. I've tried none of this myself.
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The Main Man · Posted: Mon Apr 22, 2019 1:20 pm Post subject:

The Main Man · Posted: Thu Apr 25, 2019 10:58 am Post subject:

Well, I just had to try and indeed Arch uses Non root Xorg by default.
Even tried Ubuntu 18.04 and they also have it working by default.

I think I tried everything in Gentoo to make it work, well obviously I didn't everything because I can't make it to work, but I'm out of ideas, have no idea what's going on.
Could it maybe be systemd in combination with login manager which somehow makes this work ?

Anon-E-moose · Posted: Thu Apr 25, 2019 12:00 pm Post subject:

systemd does work with non-suid X, that's because systemd is effectively running as root.
Systemd is an effort at creating windows with a linux kernel, with all that that implies.

Doesn't really help those of us not running systemd.

Edit to add: quite frankly I've given up on non-root X and just have it installed suid.
Been that way since X started and there's been no real epidemic of problems because of it.
The whole push for non-suid X only started reaching a fever pitch when X started being hosted at freedesktop.org, which also *magically* hosts systemd and associated crapola.
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The Main Man · Posted: Thu Apr 25, 2019 12:47 pm Post subject:

It's not just about security, it bugs me that it doesn't work in Gentoo, more specifically with amd gpu cards.

btw Void linux is systemd free and there seems to be working too.
Scroll all the way to the bottom , Rootless xorg
https://wiki.voidlinux.org/Xorg

The Main Man · Posted: Thu Apr 25, 2019 1:10 pm Post subject:

I found a way, might not be ideal but it seems it's the only way.

All it takes is in make.conf

DaggyStyle · Watchman Joined: 22 Mar 2006 Posts: 5909

what does startx gives you? login screen or desktop?
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The Main Man · Posted: Thu Apr 25, 2019 3:53 pm Post subject:

Desktop, actually window manager, dwm.
btw I'm not using login managers.

asturm · Developer Joined: 05 Apr 2007 Posts: 8935

DaggyStyle · Watchman Joined: 22 Mar 2006 Posts: 5909

I wonder if there is a way to make it work with login managers
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