[PATCH] arm: port KCOV to arm

[Dmitry Vyukov]

On Fri, Apr 27, 2018 at 6:18 PM, Mark Rutland <mark.rutland at arm.com> wrote:
> On Fri, Apr 27, 2018 at 03:51:22PM +0200, Dmitry Vyukov wrote:
>> On Fri, Apr 27, 2018 at 3:06 PM, Mark Rutland <mark.rutland at arm.com> wrote:
>> > Can you share your kernel config?
>>
>> Attached. It's pretty much vexpress_defconfig with few minor
>> additions. Here is full description of what I am doing:
>> https://github.com/google/syzkaller/blob/master/docs/linux/setup_linux-host_qemu-vm_arm-kernel.md
>
> Cheers!
>
>> FWIW when I do "KCOV_INSTRUMENT_fault.o := n" everything works and I
>> see reasonable coverage.
>
> While this may be the case, I think it's papering over a bug rather than
> solving it.
>
> [...]
>
>> > I can't reproduce the issue on real hardware atop of v4.17-rc2, when
>> > booting and running a standard ARMv7 buildroot userspace. So the kcov
>> > mode check seems fine to me.
>>
>> It happens after brief fuzzing with syzkaller. So it's both kcov
>> opened and some weird syscall workload. Again, here is everything what
>> I am doing:
>> https://github.com/google/syzkaller/blob/master/docs/linux/setup_linux-host_qemu-vm_arm-kernel.md
>
> I've set this up, and while I see RCU stalls and "no output from test
> machine" warnings, I'm not seeing any reports with KCOV splats.
>
> Are you somehow connecting to a VM which failed with no output?

I've started seeing assorted crashes like these:

kernel panic: Fatal exception
unable to handle kernel paging request in migrate_task_rq_fair
BUG: spinlock bad magic in corrupted
unable to handle kernel paging request in trace_hardirqs_off_caller
unable to handle kernel paging request in kick_process
kernel panic: stack-protector: Kernel stack is corrupted in: do_futex
unable to handle kernel paging request in __sanitizer_cov_trace_pc
Unable to handle kernel paging request at virtual address ADDR

Do you see code coverage increasing?

Besides compiler I am not sure what else can be different between our
setups (mine is Debian's 7.2).