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

[Kirill A. Shutemov]

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