linux-kernel - Re: [patches] [PATCH] [21/22] x86_64: Extend bzImage protocol for relocatable bzImage

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Message-ID: <m1mz0r6ohm.fsf@ebiederm.dsl.xmission.com>
Date:	Sun, 29 Apr 2007 12:10:13 -0600
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Jeremy Fitzhardinge <jeremy@...p.org>,
	Jeff Garzik <jeff@...zik.org>, Andi Kleen <ak@...e.de>,
	patches@...-64.org, Vivek Goyal <vgoyal@...ibm.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [patches] [PATCH] [21/22] x86_64: Extend bzImage protocol for relocatable bzImage

"H. Peter Anvin" <hpa@...or.com> writes:

> Jeremy Fitzhardinge wrote:
>> Eric W. Biederman wrote:
>>> All it does is set a flag that tells a bootloader.
>>> "Hey. I can run when loaded a non-default address, and this is what
>>>  you have to align me to."
>>>
>>> All relocation processing happens in the kernel itself.
>>>   
>> 
>> Is it possible to decompress and extract the kernel image from the
>> bzImage without executing it?  Ie, is there enough information to find
>> the compressed data part of the bzImage by inspection?
>> 
>> At some point we'll need to change the Xen domain builder to handle
>> bzImage files, and it would be best if we didn't need to run them.
>> 
>
> Probabilistically, you might be able to (search for a gzip header), but
> it is *definitely* not guaranteed by protocol.

I suspect the issue isn't so much skipping the decompression
but either getting at the Xen ELF notes or bypassing privileged instructions.


Eric
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