> On 09/20/16 18:07, H. Peter Anvin wrote: > > > >> - vvar is highly magical. IMO letting it get mapped with VM_MAYWRITE > >> is asking for trouble, as anything that writes it will COW it, leading > >> to strange malfunctions. > >> > > The vvar page obviously needs to be mapped MAP_SHARED, and the > underlying file needs to reject writes. A solution where this area > doesn't end up MAP_SHARED is obviously defective.
Hmm, maybe. But it does certainly work now, and I'm not sure what we gain by making it more file-like than needed. Using a non-null vm_file removes tons of special cases, but giving it a real address_space doesn't seem very useful to me. > > As far as keeping the user from doing really stupid things... they can > map a RAM page over the vvar area and there is nothing the kernel really > can do to keep them from doing something like that without doing things > that are probably way worse than the disease. At least it will be > obvious looking at the mapping file what is going on. I don't want an overly clever debugger to poke the page. MAP_SHARED might be sufficient.
