Re: [GIT PULL] x86/kaslr for v3.14

[Ingo Molnar <mingo@kernel.org>]

* H. Peter Anvin <hpa@zytor.com> wrote:

> > The thing is, one of my first remarks on this whole KASLR series 
> > was that tooling needs to work. I suggested that the kernel should 
> > only expose non-randomized addresses and that all facilities need 
> > to continue to 'just work' with those. That argument was ignored 
> > AFAICS and the problem still isn't solved.
> > 
> > I'd argue that solving it in the kernel instead of making all 
> > tooling variants aware of KASLR one by one is a far more 
> > intelligent and efficient solution ...
> 
> Not ignored, but found not to really work all that well (we had that 
> discussion in the context of relocated kernels, too.)  The problem 
> you end up with is that as soon as you run into situations where you 
> have to deal with pointers during debugging, be it using kgdb, stack 
> dumps or whatever, all the work that you have done in the kernel to 
> try to hide relocation from the debug infrastructure all of a sudden 
> becomes a huge liability, and ends up backfiring in a horrific way.

The thing is, that 'huge liability' is now pushed into tooling, which 
isn't in any better position to judge a piece of data in a backtrace 
than the kernel - in fact it's in an arguably worse position, as it 
does not generate that data.

kgdb is an entirely different animal, I'm talking about the 99% 
usecase: code profiling and tooling interpreting code addresses that 
come from the kernel.

Thanks,

	Ingo