Re: [PATCHv2 1/2] x86/mm: Do not allow non-MAP_FIXED mapping across DEFAULT_MAP_WINDOW border

[Thomas Gleixner]

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;

Thanks,

        tglx