linux-kernel - Re: + fully-honor-vdso_enabled.patch added to -mm tree

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Message-ID: <45E8A300.9020001@redhat.com>
Date:	Fri, 02 Mar 2007 17:19:44 -0500
From:	Chuck Ebbert <cebbert@...hat.com>
To:	John Reiser <jreiser@...Wagon.com>
CC:	Oleg Nesterov <oleg@...sign.ru>, Andi Kleen <ak@...e.de>,
	Ingo Molnar <mingo@...e.hu>,
	Arjan van de Ven <arjan@...radead.org>,
	Paul Mundt <lethal@...ux-sh.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: + fully-honor-vdso_enabled.patch added to -mm tree

John Reiser wrote:
> The value of ->sysenter_return is interpreted in user space by the
> sysexit instruction; nobody else cares what the value is.  The kernel
> is not required to provide a good value when vdso_enabled is zero,
> because the kernel has not told the process that sysenter is valid
> (by setting AT_SYSINFO.)

Doesn't matter because a malicious user can still execute sysenter.
We do have to deal with that somehow, so we have to put something
safe in there.

> Correct.  Changing vdso_enabled from 0 to non-zero must be prepared
> to lose this race if it is not prevented.  Ordinarily it won't matter
> because the administrator will perform such changes at a "quiet" time.
> 

We have to deal with all the possibilities here, too.
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