linux-kernel - Re: [PATCH 6/6] x86: kaslr: relocate base offset at boot

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Message-ID: <CAE9FiQXZcXpyEqHvON0D3u2ivcWQo1=rC1kkt5GLU4rEYaVoQw@mail.gmail.com>
Date:	Mon, 15 Apr 2013 15:57:09 -0700
From:	Yinghai Lu <yinghai@...nel.org>
To:	Kees Cook <keescook@...omium.org>
Cc:	"H. Peter Anvin" <hpa@...or.com>,
	Eric Northup <digitaleric@...gle.com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"kernel-hardening@...ts.openwall.com" 
	<kernel-hardening@...ts.openwall.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"the arch/x86 maintainers" <x86@...nel.org>,
	Jarkko Sakkinen <jarkko.sakkinen@...el.com>,
	Matthew Garrett <mjg@...hat.com>,
	Matt Fleming <matt.fleming@...el.com>,
	Dan Rosenberg <drosenberg@...curity.com>,
	Julien Tinnes <jln@...gle.com>, Will Drewry <wad@...omium.org>
Subject: Re: [PATCH 6/6] x86: kaslr: relocate base offset at boot

On Mon, Apr 15, 2013 at 3:42 PM, Kees Cook <keescook@...omium.org> wrote:
> On Mon, Apr 15, 2013 at 3:38 PM, Yinghai Lu <yinghai@...nel.org> wrote:
>
>> so the decompressed image is not moved high?
>
> No, I mean the size of the relocated image is using z_extract_offset
> as the end size of the relocated memory. See select_aslr_address. It
> takes the chosen aslr offset plus the location of z_extract_offset and
> keeps reducing the offset until it's inside the physical end of
> memory.

My point is:
If you move the decompressed high, for example, before aslr uncompressed
vmlinx is on [1024g+16M, 1024g+256M).
after aslr, it is on [1024g+16M + 32M, 1024g+256M + 32M).

You will need to make sure that 32M is still RAM in e820 memmap.
also those range should not be with boot_param, command line, and initrd.
as bootloader could put boot_param, commandline and initrd in that 32M range.

Yinghai
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