Re: Re: [Linux-fbdev-devel] Redesign of kernel graphics interface

["Ville Syrjälä" <syrjala@sci.fi>]

On Sat, May 15, 2004 at 09:27:34AM +0200, Holger Waechtler wrote:
> Ville Syrjälä wrote:
> >On Fri, May 14, 2004 at 11:40:04AM -0700, Jon Smirl wrote:
> >
> >>Does DirectFB work on anything beside Matrox now?
> >
> >
> >It works on any card with a working fbdev driver (vga16fb excluded). 
> >Hardware acceleration is available on quite a few chips these days.
> >
> >ati128  cyber5k  mach64  neomagic  nvidia  savage  tdfx
> >cle266  i810     matrox  nsc       radeon  sis315
> 
> Keep in mind that beside the matrox driver almost none of them 
> implements the full accelerated 2D API

cle266 is about the same level as matrox. I could get mach64 into this 
group with some modifications to the memory allocator. I think for some of 
the other drivers the biggest problem is lack of developers.

> and that most are misusing the 3D 
> engine to implement 2D functionality. Alpha blended stretch blits are 
> almost always implemented using the 3D texture engines on PC graphics cards.

I don't consider that mis-use, simply use.

> About one third of these drivers have been written using specs and 
> documentation files that have never been officially released by the 
> hardware vendors, so I'm not really sure whether they are much better 
> from a security point of view than a closed source driver -- what's the 
> point of a open source hardware driver without hardware specs? - you're 
> not really able to review it seriously.

I don't think the specs would help in that regard much. For all you know 
the specs could be all wrong. If you have the code and can see the 
expected results that usually means the code works correctly. And closed 
source kernel drivers could do a lot of other nasty stuff even without 
touching the hardware.

> The specs for the remaining ones usually showed up as soon the hardware 
> was getting outdated. Basically the same situation like the one you see 
> with DRI drivers.

Except now the specs are getting harder to get even for old hardware. The 
vendors seem to be returning to the old ways :(

> >I use matrox and mach64 drivers daily. It's been a few years since I 
> >seriously used XFree86.
> 
> Have you ever thought about the inherent security risks of memory mapped 
> i/o registers when executing non-trusted applications? Imagine what 
> happens if every single application is allowed to program the blitter 
> and texture engines to copy host memory from anywhere in the system to 
> graphics memory and back - a single misbehaving application can damage 
> your entire system.

I am aware of the risks. Currently it's not an issue for me. And if I 
limit myself to running only XDirectFB the risk is equal to running 
accelerated XFree86. Of course I would be glad to make it all secure but 
only without losing any of the nice features.

> And do you really have the time to review every line of code you execute 
> on your system?

Clearly not. There is some stuff you just have to trust (or not care).

> >>2) mesa supports a broad number of cards, basically everything there is 
> >>doc for
> >
> >
> >Just about as broad as DirectFB.
> 
> be honest.

I am. This is the list of drivers in Mesa cvs:
i810   mga     radeon  tdfx 
ffb    i830    r128  savage  unichrome
gamma  mach64  r200  sis

The list is almost the same as the DirectFB driver list. Granted that some 
of the Mesa drivers use more of the hardware's capabilities, but that's 
only because I don't have the hardware ;)

> >I'm not suggesting that everyone start using DirectFB. Everyong should be 
> >able to use any API they want. The kernel should provide just enough to 
> >allow these APIs to be implemented.
> 
> that would be always possible, don't worry.

I do worry a bit because of this OpenGL as the one and only API talk.

> Please keep in mind that we developed DirectFB at Convergence as API to 
> access SettopBox and Game Console functionality in a convenient way, it 
> was never intended and has not been designed for use in 
> security-critical desktop or workstation environments.

I am aware of that and that's why I don't recommend it to everyone. 
Personally I just find it to my liking. Even the code itself makes me 
a happy camper whereas XFree86 code gives me a headache...

-- 
Ville Syrjälä
syrjala@sci.fi
http://www.sci.fi/~syrjala/


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