On Fri, Jan 05, 2018 at 02:12:33AM -0800, Kees Cook wrote: > On Thu, Jan 4, 2018 at 9:33 PM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote: > > On Thu, Jan 4, 2018 at 12:43 PM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote: > >> > >>> On Jan 4, 2018, at 12:29 PM, Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: > >>> > >>>> On Thu, Jan 4, 2018 at 12:16 PM, Thomas Voegtle <tv@xxxxxxxx> wrote: > >>>> > >>>> Attached a screenshot. > >>>> Is that useful? Are there some debug options I can add? > >>> > >>> Not much of an oops, because the SIGSEGV happens in user space. The > >>> only reason you get any kernel stack printout at all is because 'init' > >>> dying will make the kernel print that out. > >>> > >>> The segfault address for init looks like the fixmap area to me (first > >>> byte in the last page of the fixmap?). "Error 5" means that it's a > >>> user-space read that got a protection fault. So it's not a LDT of GDT > >>> update or anything like that, it's a normal access from user space (or > >>> a qemu emulation bug, but that sounds unlikely). > >>> > >>> Is that the vsyscall page? > >>> > >>> Adding Luto to the participants. I think he noticed one of the > >>> vsyscall patches missing earlier in the 4.9 series. Maybe the 4.4 > >>> series had something similar.. > >>> > >> > >> That's almost certainly it. > >> > >> I'll try to find some time today or tomorrow to add a proper selftest. > >> > > > > Give this a shot: > > > > https://git.kernel.org/pub/scm/linux/kernel/git/luto/linux.git/commit/?h=x86/pti&id=17c5ebeb2e00879b0af1a9c32bf37ecdd9b9b31b > > > > Boot with each of vsyscall=none, vsyscall=native, and vsyscall=emulate > > and run both the 32-bit and 64-bit variants of that test. All six > > combinations should pass. But I bet they don't on 4.4. > > With my 4.4.110-rc1 under QEMU -cpu=host (Xeon E5-2690 v3) > > vsyscall=emulate: > > # ./test_vsyscall_64 > ... > [RUN] Checking read access to the vsyscall page > [FAIL] We don't have read access, but we should > > vsyscall=native: > > # ./test_vsyscall_64 > ... > [RUN] Checking read access to the vsyscall page > [FAIL] We don't have read access, but we should > > Everything else passes. I get this same error with the latest 4.9-rc tree as well, but it works just fine on 4.15-rc6. I'll look at the proposed patches now for this... thanks so much for the test tool. greg k-h