Re: [RFC][PATCH] linux-2.5.34_vsyscall_A0

[george anzinger <george@mvista.com>]

Linus Torvalds wrote:
> 
> On Fri, 18 Oct 2002, Andrea Arcangeli wrote:
> 
> > On Fri, Oct 18, 2002 at 09:45:41AM -0700, george anzinger wrote:
> > > Stephen Hemminger wrote:
> > > > current cpu (and maybe current pid) somehow.  And it would be possible
> > > > to avoid  preemption while in a vsyscall text page, some other Unix
> > > > variants do this to implement portions of the thread library in kernel
> > > > provided user text pages.
> > > >
> > > Now there is an idea!  Lock preemption in user space if and
> >
> > sounds not good to me, you would miss a wakeup and you would delay the
> > schedule of 1/HZ in the worst (close to the common) case.
> 
> That's not the real problem.
> 
> The real problem is that somebody can jump into the middle of a function
> (or even into the middle of an instruction), causing the function to do
> something totally different from the intended effect.
> 
> In particular, it can cause the function to loop forever.
> 
> If you disable preemption of user space, you now killed the machine.
> 
> In short - others may do it, but it's a total _DISASTER_ from a security
> and stability standpoint. Don't go there.

Oops, hadn't thought of that.  Back out, undo, etc. :)

-- 
George Anzinger   george@mvista.com
High-res-timers: 
http://sourceforge.net/projects/high-res-timers/
Preemption patch:
http://www.kernel.org/pub/linux/kernel/people/rml