From: Jamie Lokier <jamie@shareable.org>
To: Scott Wood <scott@timesys.com>
Cc: Russell King <rmk+lkml@arm.linux.org.uk>,
Ian Molton <spyro@f2s.com>,
linux-arm-kernel@lists.arm.linux.org.uk,
linux-kernel@vger.kernel.org
Subject: Re: A question about PROT_NONE on ARM and ARM26
Date: Fri, 2 Jul 2004 00:53:54 +0100 [thread overview]
Message-ID: <20040701235354.GD8950@mail.shareable.org> (raw)
In-Reply-To: <20040701152728.GA20634@yoda.timesys>
Scott Wood wrote:
> > However, plain ldr and str instructions will access the page, but
> > get_user/put_user doesn't use them, and copy_from_user/copy_to_user
> > are carefully crafted to ensure that we hit the necessary permission
> > checks for each page it touches on the first access.
>
> What if CONFIG_PREEMPT is enabled, and you get preempted after that
> first access, and another thread unmaps the page before you're
> finished with it?
The code in uaccess.S:__arch_copy_{from,to}_user doesn't disable
pre-emption, and neither does its caller.
Pages can be unmapped just due to background paging. I.e. it's a
normal occurrence, it doesn't require anything contrived.
So I think you're right: that looks like a bug.
The ARM uaccess code was written before CONFIG_PREEMPT was added, and
this couldn't happen then. It could panic a kernel now. I wonder why
it hasn't been noticed. Maybe nobody turns on CONFIG_PREEMPT on ARM?
-- Jamie
next prev parent reply other threads:[~2004-07-01 23:54 UTC|newest]
Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top
2004-06-30 2:44 A question about PROT_NONE on ARM and ARM26 Jamie Lokier
2004-06-30 3:38 ` William Lee Irwin III
2004-07-01 3:26 ` Testing PROT_NONE and other protections, and a surprise Jamie Lokier
2004-07-01 3:35 ` William Lee Irwin III
2004-07-01 4:01 ` Jamie Lokier
2004-07-01 3:44 ` Kyle Moffett
2004-07-01 4:11 ` Jamie Lokier
2004-07-01 4:59 ` Kyle Moffett
2004-07-01 12:39 ` Jamie Lokier
2004-07-01 14:43 ` [OT] " Kyle Moffett
2004-07-01 14:50 ` Jamie Lokier
2004-07-01 15:01 ` Kyle Moffett
2004-07-01 16:37 ` Matt Mackall
2004-07-01 17:26 ` Michael Driscoll
2004-07-02 7:37 ` Gabriel Paubert
2004-07-01 12:52 ` Russell King
2004-07-01 14:26 ` Richard Curnow
2004-06-30 8:16 ` A question about PROT_NONE on ARM and ARM26 Russell King
2004-06-30 14:59 ` Jamie Lokier
2004-06-30 15:22 ` Ian Molton
2004-06-30 18:26 ` Russell King
2004-06-30 19:14 ` Jamie Lokier
2004-06-30 19:23 ` Russell King
2004-06-30 20:15 ` Jamie Lokier
2004-06-30 22:59 ` Russell King
2004-06-30 23:30 ` Jamie Lokier
2004-06-30 23:48 ` Ian Molton
2004-07-01 1:59 ` Jamie Lokier
2004-07-01 1:05 ` Nicolas Pitre
2004-07-01 1:50 ` Jamie Lokier
2004-07-02 18:39 ` Russell King
2004-07-01 15:27 ` Scott Wood
2004-07-01 23:53 ` Jamie Lokier [this message]
2004-07-02 14:36 ` Scott Wood
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