On Fri, Dec 15, 2017 at 04:20:31PM -0800, Linus Torvalds wrote: > On Thu, Dec 14, 2017 at 11:51 PM, Peter Zijlstra <pet...@infradead.org> wrote: > > > > So we actually need the pte_access_permitted() stuff if we want to > > ensure we're not stepping on !PAGE_USER things. > > We really don't. Not in that complex and broken format, and not for every > level. > > Also, while I think we *should* check the PAGE_USER bit when walking > 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 > > (b) not tie it together with this issue at all, since the PAGE_USER > 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).
Details, please - how *can* access_ok() be taught of that?
