linux-kernel - Re: [PATCH v7u1 24/31] x86, boot: Not need to check setup_header version for setup

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Date:	Mon, 14 Jan 2013 09:37:36 -0800
From:	"H. Peter Anvin" <hpa@...or.com>
To:	Borislav Petkov <bp@...en8.de>, Yinghai Lu <yinghai@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...e.hu>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Jan Kiszka <jan.kiszka@....de>,
	Jason Wessel <jason.wessel@...driver.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7u1 24/31] x86, boot: Not need to check setup_header
 version for setup_data

On 01/14/2013 03:26 AM, Borislav Petkov wrote:
> On Thu, Jan 03, 2013 at 04:48:44PM -0800, Yinghai Lu wrote:
>> That is for bootloader.
>>
>> setup_data is in setup_header, and all bootloader is copying that
>> for bzImage. So for old bootloader should keep that as 0.
>
> Are you sure all old bootloaders have kept setup_data as 0 so that you
> can drop the check.
>
> And besides, the check doesn't hurt but prevents insane old boot loaders
> from handing in crap into the kernel so I'd leave it in.
>

No, this is a case of cargo-cult programming.  I asked Yinghai to remove it.

It is cargo-cult programming because the value of boot_params.hdr comes 
from the kernel itself, so all you're doing is telling you the boot 
protocol version associated with the kernel itself, which we already know.

If we find a bootloader that does that incorrectly (e.g. if kexec were 
to blindly copy struct boot_params from the older kernel... which 
ironically would be better than the current situation) then the right 
thing to do would be to have a central place which scrub out the fields 
and just force them to zero rather than putting a bunch of tests all 
over the place.

	-hpa

-- 
H. Peter Anvin, Intel Open Source Technology Center
I work for Intel.  I don't speak on their behalf.

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