On Wed 13-12-17 04:50:53, Matthew Wilcox wrote: > On Wed, Dec 13, 2017 at 10:25:49AM +0100, Michal Hocko wrote: > > +++ b/mm/mmap.c > > @@ -1342,6 +1342,10 @@ unsigned long do_mmap(struct file *file, unsigned long addr, > > if (!(file && path_noexec(&file->f_path))) > > prot |= PROT_EXEC; > > > > + /* force arch specific MAP_FIXED handling in get_unmapped_area */ > > + if (flags & MAP_FIXED_SAFE) > > + flags |= MAP_FIXED; > > + > > if (!(flags & MAP_FIXED)) > > addr = round_hint_to_min(addr); > > > > We're up to 22 MAP_ flags now. We'll run out soon. Let's preserve half > of a flag by giving userspace the definition: > > #define MAP_FIXED_SAFE (MAP_FIXED | _MAP_NOT_HINT) I've already tried to explain why this cannot be a modifier for MAP_FIXED. Read about the backward compatibility note... Or do I misunderstand what you are saying here? > then in here: > > if ((flags & _MAP_NOT_HINT) && !(flags & MAP_FIXED)) > return -EINVAL; > > Now we can use _MAP_NOT_HINT all by itself in the future to mean > something else. -- Michal Hocko SUSE Labs
