On Fri, Nov 18, 2016 at 9:47 AM, Christoph Lameter <cl@xxxxxxxxx> wrote: > On Thu, 17 Nov 2016, Michael Ellerman wrote: > >> Currently ZERO_OR_NULL_PTR() uses a trick of doing a single check that >> x <= ZERO_SIZE_PTR, and ignoring the fact that it also matches 1-15. > > Well yes that was done so we do not add too many branches all over the > kernel..... There are actually very few callers of this macro. (Though it's possible they're executed frequently.) >> That no longer really works once we add the poison delta, so split it >> into two checks. Assign x to a temporary to avoid evaluating it >> twice (suggested by Kees Cook). > > And now you are doing just that. In this case, what about the original < ZERO_SIZE_PTR check Michael suggested? At least the one use in usercopy.c needs to be fixed, but otherwise, it should be fine? -Kees -- Kees Cook Nexus Security -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>