Linus Torvalds writes: (Summary)
Also, while I think we *should* check the PAGE_USER bit when walking
the page tables, like we used to, we should
the page tables, like we used to, we should
(a) do it much more simply, not with that broken interface that takes insane and pointless flags
insane and pointless flags
(b) not tie it together with this issue at all, since the PAGE_USER thing really is largely immaterial.
thing really is largely immaterial.
The fact is, if we have non-user mappings in the user part of the address space, we _need_ to teach access_ok() about them, because fundamentally any "get_user()/put_user()" will happily ignore the lack of PAGE_USER (since those happen from kernel space).
the page tables, like we used to, we should
(a) do it much more simply, not with that broken interface that takes insane and pointless flags
insane and pointless flags
(b) not tie it together with this issue at all, since the PAGE_USER thing really is largely immaterial.
thing really is largely immaterial.
The fact is, if we have non-user mappings in the user part of the address space, we _need_ to teach access_ok() about them, because fundamentally any "get_user()/put_user()" will happily ignore the lack of PAGE_USER (since those happen from kernel space).