On Thu, Jan 4, 2018 at 12:43 PM, Andy Lutomirski <l...@amacapital.net> wrote: > >> On Jan 4, 2018, at 12:29 PM, Linus Torvalds <torva...@linux-foundation.org> >> wrote: >> >>> On Thu, Jan 4, 2018 at 12:16 PM, Thomas Voegtle <t...@lio96.de> 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.
