Re: ARM: vmsplit 4g/4g

afzal mohammed
2020-06-08T11:18:44Z

Hi,

On Sun, Jun 07, 2020 at 09:26:26PM +0200, Arnd Bergmann wrote:

> I think you have to use get_user_pages() though instead of
> get_user_pages_fast(),
> in order to be able to check the permission bits to prevent doing a
> copy_to_user()
> into read-only mappings.

i was not aware of this, is it documented somewhere ?, afaiu,
difference b/n get_user_pages_fast() & get_user_pages() is that fast
version will try to pin pages w/o acquiring mmap_sem if possible.

> Do you want me to review the uaccess patch to look for any missing
> corner cases, or do you want to do the whole set of user access helpers
> first?

i will cleanup and probably post RFC initially for the changes
handling copy_{from,to}_user() to get feedback.

Regards
afzal