[PATCH 3/4] drivers/misc: Add ASpeed LPC control driver

Benjamin Herrenschmidt benh at kernel.crashing.org
Fri Jan 13 03:31:30 AEDT 2017

On Thu, 2017-01-12 at 17:26 +0100, Greg KH wrote:
> I think, you can change things after access_ok() happens, there used to
> be bugs in that area a few years ago.  I think we fixed them by moving
> the offending drivers to use copy_*() instead.

Ok, I'm surprised though, we still have a metric ton of code,
especially in filesystems, who do access_ok. Generally the idea here is
that the enforcement is done by the MMU normally via the permission in
the page tables. access_ok() is simply needed to make sure we access
the portion of the page tables representing user space, not kernel
space, and that is a pretty fixed dichotomy.

Anyway, this is academic, I agree that copy_to/from_... is nicer.


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