Re: A question about PROT_NONE on ARM and ARM26

[Russell King]

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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