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From: Linus Torvalds <torvalds@linux-foundation.org>
To: Oleg Nesterov <oleg@tv-sign.ru>
Cc: Chuck Ebbert <76306.1226@compuserve.com>,
	Ingo Molnar <mingo@elte.hu>, Roland McGrath <roland@redhat.com>,
	linux-kernel@vger.kernel.org
Subject: Re: Q: a bogus set_fs(USER_DS) in setup_frame/setup_rt_frame ?
Date: Tue, 17 Jul 2007 09:05:57 -0700 (PDT)	[thread overview]
Message-ID: <alpine.LFD.0.999.0707170902570.19166@woody.linux-foundation.org> (raw)
In-Reply-To: <20070717154638.GA342@tv-sign.ru>



On Tue, 17 Jul 2007, Oleg Nesterov wrote:
>
> I am really puzzled by set_fs(USER_DS) in setup_frame/setup_rt_frame.
> 
> How is it possible that current->addr_limit != USER_DS ? If this _is_
> possible, how can can we trust the result of access_ok() above?

Heh. I think it's entirely historical.

Please realize that the whole reason that function is called "set_fs()" is 
that it literally used to set the %fs segment register, not 
"->addr_limit".

So I think the "set_fs(USER_DS)" is there _only_ to match the other

        regs->xds = __USER_DS;
        regs->xes = __USER_DS;
        regs->xss = __USER_DS;
        regs->xcs = __USER_CS;

things, and never mattered. And now it matters even less, and has been 
copied to all other architectures where it is just totally insane.

		Linus

  parent reply	other threads:[~2007-07-17 16:07 UTC|newest]

Thread overview: 5+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2007-07-17 15:46 Oleg Nesterov
2007-07-17 16:04 ` [patch] i386: remove unnecessary code Ingo Molnar
2007-07-17 16:05 ` Linus Torvalds [this message]
2007-07-17 17:15   ` Q: a bogus set_fs(USER_DS) in setup_frame/setup_rt_frame ? Oleg Nesterov
2007-07-17 19:36     ` David Miller

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