linux-kernel - Re: [PATCH 2/4] kaslr: check if the random addr is available

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Message-ID: <20140910135555.GA1887@dhcp-17-102.nay.redhat.com>
Date:	Wed, 10 Sep 2014 21:55:55 +0800
From:	Baoquan He <bhe@...hat.com>
To:	Vivek Goyal <vgoyal@...hat.com>
Cc:	Kees Cook <keescook@...omium.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Andi Kleen <ak@...ux.intel.com>,
	Ingo Molnar <mingo@...hat.com>,
	Thomas Deutschmann <whissi@...ssi.de>,
	Dave Young <dyoung@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	WANG Chao <chaowang@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH 2/4] kaslr: check if the random addr is available

On 09/09/14 at 03:41pm, Vivek Goyal wrote:
> On Sat, Sep 06, 2014 at 06:16:57AM +0800, Baoquan He wrote:
> 
> [CC hpa ]
> 
> > Hi Kees,
> > 
> > Yes, process_e820_entry() can make sure the choice+output_len <
> > CONFIG_RANDOMIZE_BASE_MAX_OFFSET, but that can't stop other bootloaders
> > to put kernel in region above CONFIG_RANDOMIZE_BASE_MAX_OFFSET.
> > 
> > E.g in kdump, we can set crashkernel=256M@...4M in cmdline. Then the 1st
> > kernel will reserve 256M memory just at 1024M place. So if load kdump
> > kernel now, the output will be 1024M before choose_kernel_location().
> > With this value, output won't be changed in choose_kernel_location(),
> > then it will do decompress(), then call handle_relocations(). Then since
> > 1024 is not equal to LOAD_PHYSICAL_ADDR, it will start relocatoins
> > handling. And this cause _text stamping into MODULES vaddr range. System
> > will be exceptional.
> 
> Bao,
> 
> If you apply your first patch where output_orig == output, then
> handle_relocations() will not do anything for x86_64 case and bail
> out. That should take care of this issue. Isn't it? And we should
> not require this patch.

Yes, exactly.

> 
> Thanks
> Vivek
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