Messages in this thread | | | Subject | Re: linux-next: Tree for Nov 7 | From | Khalid Aziz <> | Date | Mon, 13 Nov 2017 09:35:22 -0700 |
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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.
-- Khalid
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