linux-kernel - Re: [4/6] go BUG on vmallocspace in __pa() (was: Re: [-mm patch] i386: enable 4k stacks by default)

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Date:	Mon, 30 Apr 2007 12:26:02 -0700
From:	Bill Irwin <bill.irwin@...cle.com>
To:	Alan Cox <alan@...rguk.ukuu.org.uk>
Cc:	Andi Kleen <andi@...stfloor.org>,
	Christoph Hellwig <hch@...radead.org>,
	David Chinner <dgc@....com>, Zan Lynx <zlynx@....org>,
	Adrian Bunk <bunk@...sta.de>,
	Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [4/6] go BUG on vmallocspace in __pa() (was: Re: [-mm patch] i386: enable 4k stacks by default)

On Mon, Apr 30, 2007 at 10:38:19AM -0700, William Lee Irwin III wrote:
>>>> Here's what I did for i386 for someone concerned about blowing the
>>>> stack.

On Mon, Apr 30, 2007 at 10:45:10AM -0700, William Lee Irwin III wrote:
>>> Add checks to __pa() so it goes BUG() on vmallocspace addresses.

On Mon, 30 Apr 2007 20:52:42 +0200 Andi Kleen <andi@...stfloor.org> wrote:
>> Sorry I think that's too costly to do. __pa is pretty common

On Mon, Apr 30, 2007 at 08:20:59PM +0100, Alan Cox wrote:
> But not too costly to do if it is done solely with vmalloc the stack
> for
> debug purposes. The bigger problem with the vmalloc approach is there
> are
> still offenders who DMA off the kernel stack on i386 although I'd hope
> they are all ancient... we'll find out with this anyway

Sorry about the email address switch. This is actually work-related.

The stack vmalloc() and __pa() patches were partially intended to catch
or otherwise deliberately break such offenders and go BUG() on them. The
__pa() check in particular is exclusively for the purpose of catching
them. The primary motive being the stack vmalloc() patches remained, of
course, establishing a guard page to trap stack overflows.


-- wli
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