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SubjectRe: [PATCHv2 1/2] x86/mm: Do not allow non-MAP_FIXED mapping across DEFAULT_MAP_WINDOW border
On Tue, Nov 14, 2017 at 09:54:52PM +0100, Thomas Gleixner wrote:
> On Tue, 14 Nov 2017, Kirill A. Shutemov wrote:
>
> > On Tue, Nov 14, 2017 at 05:01:50PM +0100, Thomas Gleixner wrote:
> > > @@ -198,11 +199,14 @@ arch_get_unmapped_area_topdown(struct fi
> > > /* requesting a specific address */
> > > if (addr) {
> > > addr = PAGE_ALIGN(addr);
> > > + if (!mmap_address_hint_valid(addr, len))
> > > + goto get_unmapped_area;
> > > +
> >
> > Here and in hugetlb_get_unmapped_area(), we should align the addr after
> > the check, not before. Otherwise the alignment itself can bring us over
> > the borderline as we align up.
>
> Hmm, then I wonder whether the next check against vm_start_gap() which
> checks against the aligned address is correct:
>
> addr = PAGE_ALIGN(addr);
> vma = find_vma(mm, addr);
>
> if (end - len >= addr &&
> (!vma || addr + len <= vm_start_gap(vma)))
> return addr;

I think the check is correct. The check is against resulting addresses
that end up in vm_start/vm_end. In our case we want to figure out what
user asked for.

--
Kirill A. Shutemov

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