On Thu, Nov 17, 2016 at 3:36 PM, Josh Poimboeuf <jpoim...@redhat.com> wrote: > On Thu, Nov 17, 2016 at 09:25:58AM -0500, Vince Weaver wrote: >> On Thu, 17 Nov 2016, Josh Poimboeuf wrote: >> >> > On Thu, Nov 17, 2016 at 10:48:27AM +0100, Dmitry Vyukov wrote: >> > > Just in case, there is currently a known KASAN false positive related >> > > to longjmp's on GPFs. When a syscall hits GPF stack is unwound to >> > > kernel entry point, this leaves a bunch of stray poisoned redzones on >> > > the thread stack. They later cause false stack-out-of-bounds reports. >> > > >> > > But this does not seem to be the case here. Kernel is not tainted. And >> > > shadow at the bottom of the reports looks sane. >> > > >> > > But if that's the case somehow, we will need to add >> > > kasan_unpoison_remaining_stack() call before a longjmp like we did for >> > > jprobe_return(): >> > > https://groups.google.com/d/msg/kasan-dev/Hzox58yZ4MU/TOdFoWMuBQAJ >> > >> > I'm pretty sure this isn't a KASAN false positive. The unwinder does >> > actually seem to be accessing a bad area of the stack, in the middle of >> > a function's stack frame. >> >> I'm having trouble reproducing it on a few other machines I have fuzzing. >> So there might be some kernel option contributing, I need to compare >> .configs. >> >> Also the machine that easily triggers the problem I'm compiling with >> gcc-5.4 where the machines I can't are using gcc-4.9. > > I believe KASAN only works with gcc 5 and later, so that would explain > why you aren't seeing it with gcc 4.9.
Right. 4.9 has limited support for KASAN. It supports general instrumentation, but only with CONFIG_KASAN_OUTLINE, and it does not support stack poisoning. Which is required to detect stack OOBs.
