Re: [PATCH 4.4 00/37] 4.4.110-stable review

[Andy Lutomirski]

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.