linux-kernel - Re: Bug: fio traps into kernel without exiting because futex has a deadloop

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Date:	Mon, 15 Jun 2009 10:27:02 +0200 (CEST)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	"Zhang, Yanmin" <yanmin_zhang@...ux.intel.com>
cc:	Peter Zijlstra <peterz@...radead.org>,
	Darren Hart <dvhltc@...ibm.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: Bug: fio traps into kernel without exiting because futex has a
 deadloop

On Mon, 15 Jun 2009, Zhang, Yanmin wrote:
> On Fri, 2009-06-12 at 10:39 +0200, Thomas Gleixner wrote:
>
> > +	ret = get_user_writeable(uaddr);
>
> X86 pte entry has no READABLE flag. Other platforms might have. If their pte
> only set WRITE flag, Is it poosible to create a similiar DOS attack with
> WRITEONLY area on such platforms?

Just checked with Peter. The kernel assumes that when its present we
can read. We looked at the arches that do support wr-only and it seems
that this is a valid assumption. i.e. we don't support wr-only
mappings.

Thanks,

	tglx
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