linux-kernel - Re: [PATCH] THE LINUX/I386 BOOT PROTOCOL

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Date:	Mon, 28 Aug 2006 09:02:16 +0300
From:	Alon Bar-Lev <alon.barlev@...il.com>
To:	"H. Peter Anvin" <hpa@...or.com>
CC:	Andi Kleen <ak@...e.de>, Andrew Morton <akpm@...l.org>,
	linux-kernel@...r.kernel.org, johninsd@....rr.com,
	Matt_Domsch@...l.com
Subject: Re: [PATCH] THE LINUX/I386 BOOT PROTOCOL - Breaking the 256 limit
 (ping)

H. Peter Anvin wrote:
> Found the references.  This seems to imply that EDD overwrites the area 
> used by LILO 22.6.1.  LILO 22.6.1 uses the new boot protocol, with the 
> full pointer, and seems to obey the spec as far as I can read the code. 
>  I'm going to try to run it in simulation and observe the failure that way.
> 
> However, something is still seriously out of joint.  The EDD data 
> actually overlays the setup code, not the bootsect code, and thus there 
> "shouldn't" be any way that this could interfere.  My best guess at this 
> time is that either the EDD code or LILO uses memory it's not supposed 
> to use, and the simulation should hopefully reveal that.
> 
> Sorry if I seem snarky on this, but if we can't get to the bottom of 
> this we can't ever fix it.
> 
>     -hpa
> 

I think I've found one problem... But I it should not be the major one.
The EDD code scans the command-line as fixed string.
What about something like the following?

Best Regards,
Alon Bar-Lev.

diff -urNp linux-2.6.18-rc4-mm2/arch/i386/boot/edd.S linux-2.6.18-rc4-mm2.new/arch/i386/boot/edd.S
--- linux-2.6.18-rc4-mm2/arch/i386/boot/edd.S   2006-06-18 04:49:35.000000000 +0300
+++ linux-2.6.18-rc4-mm2.new/arch/i386/boot/edd.S       2006-08-28 08:55:01.000000000 +0300
@@ -29,6 +29,8 @@
         movl    $(COMMAND_LINE_SIZE-7), %ecx
  # loop through kernel command line one byte at a time
  cl_loop:
+       cmpb    $0,(%si)
+       jz      done_cl
         cmpl    $EDD_CL_EQUALS, (%si)
         jz      found_edd_equals
         incl    %esi
-
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