On Fri, Nov 3, 2017 at 6:39 PM, Kees Cook <[email protected]> wrote: > On Fri, Nov 3, 2017 at 5:24 PM, Al Viro <[email protected]> wrote: >> On Fri, Nov 03, 2017 at 05:14:05PM -0700, Kees Cook wrote: >>> > x86 turns out to be easier since the safe and unsafe paths are mostly >>> > disjoint so we don't have to worry about gcc optimizing out access_ok. >>> > I tweaked the Kconfig to someting a bit more generic. >>> > >>> > The size increase was ~8K in text with a config I tested. >>> >>> Specifically, this feature would have caught the waitid() bug in 4.13 >>> immediately. >> >> You mean, as soon as waitid() was given a kernel address. At which point >> you'd get a shiny way to generate a BUG(), and if something like that >> happened under a mutex - it's even more fun... > > Nope, any usage at all would BUG. This would have been immediately noticed. :)
Sorry, ignore that; yes, on any kernel address. But as always reduction of impact is important: from exploitable flaw to DoS. Much better! -Kees -- Kees Cook Pixel Security
