On Fri, Oct 27, 2017 at 04:41:13PM +0100, Will Deacon wrote:

Probably a stupid question, but why not just move the access_ok check
into __{get,put}_user and remove it from {get,put}_user? We can also
then move the uaccess_{enable,disable}_not_uao calls out from the __
variants so that we can implement user_access_{begin,end}.

The intent of __{get,put}_user() is to have a fast accessor compared
to {get,put}_user() which does all the full checks.

However, with the uaccess stuff we have now by default, I don't think
it makes much sense - maybe we're better off using copy_{to,from}_user()
in those code paths and fixing up the struct in kernel space rather than
__{get,put}_user()?

I suspect that if we do have the full checks in __{get,put}_user() that
makes the case stronger for doing that - and maybe killing the __
accessors entirely.

Take a look at kernel/signal.c to see a typical usage of the __
accessors.

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