linux-kernel - Re: [PATCH] x86, boot: skip relocs when load address unchanged

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Message-ID: <20150226064511.GC4636@dhcp-16-105.nay.redhat.com>
Date:	Thu, 26 Feb 2015 14:45:11 +0800
From:	Baoquan He <bhe@...hat.com>
To:	MegaBrutal <megabrutal@...il.com>
Cc:	Kees Cook <keescook@...omium.org>,
	Linux kernel <linux-kernel@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"x86@...nel.org" <x86@...nel.org>, Vivek Goyal <vgoyal@...hat.com>,
	Jan Beulich <JBeulich@...e.com>,
	Junjie Mao <eternal.n08@...il.com>,
	Andi Kleen <ak@...ux.intel.com>, "Thomas D." <whissi@...ssi.de>
Subject: Re: [PATCH] x86, boot: skip relocs when load address unchanged

On 02/26/15 at 07:29am, MegaBrutal wrote:
> Thanks for this patch, and good to see it in mainline!
> 
> This actually fixes the problem I reported here:
> https://lkml.org/lkml/2014/12/1/15
> 
> I wish it to be backported into the Ubuntu Utopic kernel asap.
> 
> > This patch works for me. And good to see it's being merged. About the
> > patch log, I would say relocations do unexpected things when the kernel
> > is above 1G since randomization is done from 16M to 1G, namely
> > CONFIG_RANDOMIZE_BASE_MAX_OFFSET. So above 1G kernel text mapping will
> > step into kernel module mapping region.
> 
> I'm just speculating, but is it the reason why I only get problems
> when I boot with kexec? Maybe it's only then when the kernel gets
> above 1G. Otherwise, the kernels boot properly when they are booted
> from GRUB.

Yeah, kexec loads kernel at the top of physical memory. And above 1G
kernel mapping will step into module mapping area and collapse system.
Grub doesn't incur this problem.
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