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SubjectRe: linux-next: Tree for Nov 7
On Mon 13-11-17 09:35:22, Khalid Aziz wrote:
> On 11/13/2017 09:06 AM, Michal Hocko wrote:
> > OK, so this one should take care of the backward compatibility while
> > still not touching the arch code
> > ---
> > commit 39ff9bf8597e79a032da0954aea1f0d77d137765
> > Author: Michal Hocko <mhocko@suse.com>
> > Date: Mon Nov 13 17:06:24 2017 +0100
> >
> > mm: introduce MAP_FIXED_SAFE
> > MAP_FIXED is used quite often but it is inherently dangerous because it
> > unmaps an existing mapping covered by the requested range. While this
> > might be might be really desidered behavior in many cases there are
> > others which would rather see a failure than a silent memory corruption.
> > Introduce a new MAP_FIXED_SAFE flag for mmap to achive this behavior.
> > It is a MAP_FIXED extension with a single exception that it fails with
> > ENOMEM if the requested address is already covered by an existing
> > mapping. We still do rely on get_unmaped_area to handle all the arch
> > specific MAP_FIXED treatment and check for a conflicting vma after it
> > returns.
> > Signed-off-by: Michal Hocko <mhocko@suse.com>
> >
> > ...... deleted .......
> > diff --git a/mm/mmap.c b/mm/mmap.c
> > index 680506faceae..aad8d37f0205 100644
> > --- a/mm/mmap.c
> > +++ b/mm/mmap.c
> > @@ -1358,6 +1358,10 @@ unsigned long do_mmap(struct file *file, unsigned long addr,
> > if (mm->map_count > sysctl_max_map_count)
> > return -ENOMEM;
> > + /* force arch specific MAP_FIXED handling in get_unmapped_area */
> > + if (flags & MAP_FIXED_SAFE)
> > + flags |= MAP_FIXED;
> > +
> > /* Obtain the address to map to. we verify (or select) it and ensure
> > * that it represents a valid section of the address space.
> > */
>
> Do you need to move this code above:
>
> if (!(flags & MAP_FIXED))
> addr = round_hint_to_min(addr);
>
> /* Careful about overflows.. */
> len = PAGE_ALIGN(len);
> if (!len)
> return -ENOMEM;
>
> Not doing that might mean the hint address will end up being rounded for
> MAP_FIXED_SAFE which would change the behavior from MAP_FIXED.

Yes, I will move it.
--
Michal Hocko
SUSE Labs

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