Date: Wed, 30 Jun 2004 09:16:21 +0100
From: Russell King <rmk+lkml@arm.linux.org.uk>
To: Jamie Lokier <jamie@shareable.org>
Cc: 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
Message-ID: <20040630091621.A8576@flint.arm.linux.org.uk>
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	Ian Molton <spyro@f2s.com>, linux-arm-kernel@lists.arm.linux.org.uk,
	linux-kernel@vger.kernel.org
References: <20040630024434.GA25064@mail.shareable.org>
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In-Reply-To: <20040630024434.GA25064@mail.shareable.org>; from jamie@shareable.org on Wed, Jun 30, 2004 at 03:44:34AM +0100
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On Wed, Jun 30, 2004 at 03:44:34AM +0100, Jamie Lokier wrote:
> My question is: if the _kernel_ reads a PROT_NONE page, will it fault?
> It looks likely to me.

There are two different types of privileged accesses on ARM.  One is the
standard load/store instruction, which checks the permissions for the
current processor mode.  The other is one which simulates a user mode
access to the address.

We use the latter for get_user/put_user/copy_to_user/copy_from_user.

> This means that calling write() with a PROT_NONE region would succeed,
> wouldn't it?

No, because the uaccess.h function will fault, and we'll end up returning
-EFAULT.

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:  2.6 PCMCIA      - http://pcmcia.arm.linux.org.uk/
                 2.6 Serial core
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