linux-kernel - Re: [rfc] increase struct page size?!

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Date:	Mon, 21 May 2007 11:45:07 +0200
From:	Nick Piggin <npiggin@...e.de>
To:	Helge Hafting <helge.hafting@...el.hist.no>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	William Lee Irwin III <wli@...omorphy.com>,
	Christoph Lameter <clameter@....com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux Memory Management List <linux-mm@...ck.org>,
	linux-arch@...r.kernel.org
Subject: Re: [rfc] increase struct page size?!

On Mon, May 21, 2007 at 11:12:59AM +0200, Helge Hafting wrote:
> Andrew Morton wrote:
> >On Sat, 19 May 2007 11:15:01 -0700 William Lee Irwin III 
> ><wli@...omorphy.com> wrote:
> >
> >  
> >>Much the same holds for the atomic_t's; 32 + PAGE_SHIFT is
> >>44 bits or more, about as much as is possible, and one reference per
> >>page per page is not even feasible. Full-length atomic_t's are just
> >>not necessary.
> >>    
> >
> >You can overflow a page's refcount by mapping it 4G times.  That requires
> >32GB of pagetable memory.  It's quite feasible with remap_file_pages().
> >  
> But do anybody ever need to do that?
> Such an attack is easily thwarted by refusing to map it more
> than, say 3G times? 

That still allows you to DoS the page.

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