linux-kernel - Re: [tip:x86/urgent] x86: Make sure IDT is page aligned

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Message-ID: <CAGXu5jJOJTb_rd5gqZ8Omz=0V=jwONk8BRCzQN6jqO1fO6DfQg@mail.gmail.com>
Date:	Mon, 15 Jul 2013 11:37:16 -0700
From:	Kees Cook <keescook@...omium.org>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Yinghai Lu <yinghai@...nel.org>, Ingo Molnar <mingo@...nel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	pageexec@...il.com, Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	"linux-tip-commits@...r.kernel.org" 
	<linux-tip-commits@...r.kernel.org>
Subject: Re: [tip:x86/urgent] x86: Make sure IDT is page aligned

Hi,

On Mon, Jul 15, 2013 at 11:09 AM, H. Peter Anvin <hpa@...or.com> wrote:
> On 07/13/2013 02:34 PM, Yinghai Lu wrote:
>>
>> can we use put all idt_table related in to __bss.aligned section ...?
>>
>> like
>> gate_desc idt_table[NR_VECTORS] __page_aligned_bss;
>>
>
> I think this is the best solution all around... it not only solves the
> initializer problem but also reduces the size of data.
>
> A long, long time ago in a galaxy far, far away I believe the IDT got
> set up before we cleared bss, but that is no longer the case as we now
> clear bss very, very early (on 32 bits before paging is even enabled.)
>
> Still, it would seem that the minimal solution, if we need something for
> 3.11/stable, is to simply fix the alignment statement in head_64.S
> (optionally move to .bss..page_aligned) and then do the proper cleanup
> for 3.12.  If you could prepare a patch for the former (please include
> the descriptions we discussed over IRC) and a patchset for the latter it
> would be good.

Sorry for the trouble I caused on this. I've reorganized how I do test
builds now, which should hopefully cut down on my stupid mistakes.

I'll send two patches, one for 3.11/stable with the absolute minimal
change to alignment, and another for 3.12 that moves all the IDT
variables into common places using __page_aligned_bss as Yinghai Lu
recommended.

Thanks,

-Kees


--
Kees Cook
Chrome OS Security
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