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

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Date:	Tue, 21 Jan 2014 15:56:15 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Cong Ding <dinggnu@...il.com>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Ingo Molnar <mingo@...e.hu>, Kees Cook <keescook@...omium.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Mathias Krause <minipli@...glemail.com>,
	Michael Davidson <md@...gle.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Wei Yongjun <yongjun_wei@...ndmicro.com.cn>
Subject: Re: [GIT PULL] x86/kaslr for v3.14


* H. Peter Anvin <hpa@...or.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
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