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SubjectRe: kill -9 <pid of X>
Date
> Remember, we're talking about defending against signals from a hostile
> root who wants to crash the video card. In this scenario, not even the
> kernel can do it -- root can install a kernel module which overwrites

Signals are the uninteresting end of the problem, being root is uninteresting.
The bigger problems are that X11 is subject to being killed with sig 9
(which with a horrible kernel hack can be blocked for iopl3 processes)

Now you need the signal 9 blocking hack because any parent process that
sits around to catch X failures does _not_ know the exact state of the
video card.

The related problems are SAK - which is defined to kill all processes on that
VT and out of resource kills from the kernel (oom()). SAK is not that big
a deal - a setuid "sak signal" ioctl akin to the way you take over console
switching covers it. Oom is trickier.

> Boy, it's no wonder Linus is grumpy these days.

Being grumpy and being right are different things.

I'd agree however - you don't need to put all mode switching code in
kernel if you allow iopl3 proceses to lock out sig 9 and you provide
a sak hook. Oom should be solvable its just harder

Alan


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