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

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Message-ID: <20070302231103.GA249@tv-sign.ru>
Date:	Sat, 3 Mar 2007 02:11:03 +0300
From:	Oleg Nesterov <oleg@...sign.ru>
To:	Chuck Ebbert <cebbert@...hat.com>
Cc:	John Reiser <jreiser@...Wagon.com>, 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

On 03/02, Chuck Ebbert wrote:
>
> 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.

Yes, but a malicious user can't make any harm to the system, sysexit
jumps to ->sysenter_return when user_mode() is true, right?

(I am asking because I don't know in details what sysexit does).

Oleg.

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