Re: general protection fault in perf_misc_flags

[Dmitry Vyukov]

On Tue, Sep 29, 2020 at 10:33 AM Borislav Petkov <bp@xxxxxxxxx> wrote:
>
> On Mon, Sep 28, 2020 at 10:23:53PM +0200, Borislav Petkov wrote:
> > 2020/09/28 22:21:01 VMs 3, executed 179, corpus cover 11792, corpus signal 10881, max signal 19337, crashes 0, repro 0
>
> Ok, so far triggered two things:
>
> WARNING in f2fs_is_valid_blkaddr        1       2020/09/29 10:27        reproducing
> WARNING in reiserfs_put_super           1       2020/09/28 22:42
>
> you've probably seen them already.
>
> Anyway, next question. Let's say I trigger the corruption: is there a
> way to stop the guest VM which has triggered it so that I'm able to
> examine it with gdb?
>
> What about kdump? Can I dump the guest memory either with kdump or
> through the qemu monitor (I believe there's a command to dump memory) so
> that it can be poked at?
>
> Because as it is, we don't have a reproducer and as I see it, the fuzzing simply
> gets restarted:
>
> 2020/09/29 10:27:03 vm-3: crash: WARNING in f2fs_is_valid_blkaddr
> ...
> 2020/09/29 10:27:05 loop: phase=1 shutdown=false instances=1/4 [3] repro: pending=0 reproducing=1 queued=1
> 2020/09/29 10:27:05 loop: starting instance 3
>
> so it would be good to be able to say, when a vm encounters a crash, it
> should be stopped immediately so that the guest can be examined through
> qemu's gdb interface, i.e.,
>
> -gdb tcp::<portnum>
>
> or so?

Currently there is no such feature. I think some people did it because
something similar was mentioned on the mailing IIRC, but I don't know
how they did it, probably with some local code changes.