On Sunday 20 March 2005 23:30, Daniel Phillips wrote: > > Once the video memory has been mmapped, the userspace process can do > > with it whatever it wants, including accessing it while it doesn't > > have the hardware lock. > > > > So the only way to force it would be to unmap video memory whenever a > > process gives up the lock and fault it back in only if the process > > owns the lock. I don't know if there's any precedent for something > > like this in the kernel. > > There is: cluster mmap. The lock would have to be kernel based, and > passing it would be a really heavyweight operation, but this doesn't > kill the idea.
That's good to know. > > Besides, you'd only want this for window > > security, and window security has deeper issues even if you don't > > mmap the video memory. > > Assuming that we use ownership test and extend it to reads, which deeper > issues would those be? The fact that the underlying X11 protocol knows nothing about window security, so you can perform all security attacks you want without messing with mmap. Yes, we're kind of moving in a circle here. cu, Nicolai
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