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

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Date:	Fri, 07 Feb 2014 08:04:13 -0800
From:	"H. Peter Anvin" <hpa@...ux.intel.com>
To:	Vivek Goyal <vgoyal@...hat.com>, Kees Cook <keescook@...omium.org>
CC:	"H. Peter Anvin" <hpa@...or.com>,
	Richard Weinberger <richard.weinberger@...il.com>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Cong Ding <dinggnu@...il.com>, Ingo Molnar <mingo@...e.hu>,
	Ingo Molnar <mingo@...nel.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>,
	Dave Young <dyoung@...hat.com>
Subject: Re: [GIT PULL] x86/kaslr for v3.14

On 02/07/2014 06:49 AM, Vivek Goyal wrote:
> 
> Hi Kees,
> 
> Dave Young is testing kdump with kaslr enabled. He is facing some issues.
> 
> One issue he mentioned is that when second kernel boots, it might be
> placed in an area which is outside the reserved area for second kernel.
> 
> We reserve a certain memory for second kernel. And modify memory map of
> second kernel using memmap=exactmap parameter. Looks like kernel placement
> is happening before memmap=exactmap takes effect. And that seems to be
> the reason that second kernel can be placed outside the reserved memory.
> 
> IOW, memmap=exactmap and kaslr don't work together. Is it possible to
> first let memmap=exactmap take affect and then kaslr does its job. Or it
> is too late by the time memmap=exactmap is parsed.
> 
> As a workaround, Dave is currently using "nokaslr" command line parameter
> for second kernel. He is still facing issues where makedumpfile segment
> faults. He is looking into it further.
> 
> I thought I will atleast bring up with issue of memmap=exactmap and kaslr
> being incompatible.
> 

Yes, because memmap=exactmap gets parsed too late; kaslr assumes that
the e820 information passed to it is actually correct.

Yet another cause of breakage caused by the decision on the part of
kdump to rely on command-line options.

	-hpa


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