Re: [PATCH] Don't allow the stack to grow into hugetlb reserved regions

["Ken Chen" <kenchen@google.com>]

On 1/29/07, Hugh Dickins <hugh@veritas.com> wrote:
> But, never mind hugetlb, you still not quite convinced me that there's
> no problem at all with get_user_pages find_extend_vma growing on ia64.
>
> I repeat that ia64_do_page_fault has REGION tests to guard against
> expanding either kind of stack across into another region.  ia64_brk,
> ia64_mmap_check and arch_get_unmapped_area have RGN_MAP_LIMIT checks.
> But where is the equivalent paranoia when ptrace calls get_user_pages
> calls find_extend_vma?
>
> If your usual stacks face each other across the same region, they're
> not going to pose problem.  But what if someone mmaps MAP_GROWSDOWN
> near the base of a region, then uses ptrace to touch an address near
> the top of the region below?

OK, now I fully understand what you are after.  I kept on thinking in the
context of hugetlb. You are correct that ia64 does not have proper address
check for find_extend_vma() and it is indeed a potentially very bad bug in
there. I'm with you, I don't see the equivalent RGN_MAP_LIMIT check in the
get_user_pages() path.

Forwarding this to Tony as I don't have any access to ia64 machine anymore
to test/validate a fix.

    - Ken