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

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Date:	Tue, 21 Jan 2014 11:27:00 +0100
From:	Ingo Molnar <mingo@...nel.org>
To:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Adrian Hunter <adrian.hunter@...el.com>,
	Arnaldo Carvalho de Melo <acme@...radead.org>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	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


* Linus Torvalds <torvalds@...ux-foundation.org> wrote:

> On Mon, Jan 20, 2014 at 2:54 PM, Linus Torvalds
> <torvalds@...ux-foundation.org> wrote:
> > So I pulled this, but one question:
> 
> .. oh, and since I decided to test it, and was looking for problems: 
> enabling kaslr breaks "perf". The *profile* looks fine, but the 
> disassembly doesn't work.
> 
> I'm not entirely surprised. I decided I wanted to test it for a 
> reason, after all. So it's not unexpected, but perhaps people hadn't 
> thought about it, and clearly hadn't tested it.
> 
> Kernel modules disassemble fine, so clearly perf knows about code 
> that moves around, but apparently it gets surprised when the core 
> vmlinux file disassembly doesn't match addresses.

Hm, live annotation of the kernel image is a relatively new perf 
feature, and KASLR predated that (by years) - which would at least in 
part explain why it went unnoticed. (Although it does not excuse the 
lack of testing.)

I've Cc:-ed Adrian Hunter, the author of the /proc/kcore annotation 
feature.

Adrian: enabling x86 KASLR in Linus's latestest kernel via 
CONFIG_RANDOMIZE_BASE=y [this is also present in the -tip tree] breaks 
/proc/kcore annotation, because the kernel image position is now per 
bootup randomized and perf's annotation code gets surprised by that.

Thanks,

	Ingo
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