From: Jamie Lokier <jamie@shareable.org>
To: Ian Molton <spyro@f2s.com>
Cc: 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: Thu, 1 Jul 2004 02:59:02 +0100 [thread overview]
Message-ID: <20040701015902.GB1094@mail.shareable.org> (raw)
In-Reply-To: <20040701004847.3b7a173b.spyro@f2s.com>
Ian Molton wrote:
> > "ge" is a signed comparison, and unsigned is needed here, unless I
> > missed something subtle. So "bge" and "ldrge" should be "bhi" and "ldrhi".
>
> technically, I think you're right here.
>
> in practise, the arm26 address space is too small (64MB) for this to
> ever cause a problem.
No -- there is still a bug.
The bug is that userspace can pass an address like 0x90000000 to the
kernel. This is possible even on arm26.
If you follow the logic in getuser.S, it won't branch to
__get_user_bad, and it won't execute _either_ of the "ldrlst" or
"ldrge" instructions.
So it'll end up returning the value that happens to be in r1 and/or
r2, and using that for the syscall, instead of the syscall returning
-EFAULT as it should.
In rare cases, that's a security information leakage. Usually it's
just rubbish.
-- Jamie
next prev parent reply other threads:[~2004-07-01 1:59 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 [this message]
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
2004-07-02 14:36 ` Scott Wood
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