Re: Kernel Concurrency Sanitizer (KCSAN)

[Dmitry Vyukov]

On Thu, Oct 3, 2019 at 3:13 PM Dmitry Vyukov <dvyukov@xxxxxxxxxx> wrote:
>
> On Wed, Oct 2, 2019 at 9:52 PM Marco Elver <elver@xxxxxxxxxx> wrote:
> >
> > Hi Joel,
> >
> > On Tue, 1 Oct 2019 at 23:19, Joel Fernandes <joel@xxxxxxxxxxxxxxxxx> wrote:
> > >
> > > On Fri, Sep 20, 2019 at 04:18:57PM +0200, Marco Elver wrote:
> > > > Hi all,
> > > >
> > > > We would like to share a new data-race detector for the Linux kernel:
> > > > Kernel Concurrency Sanitizer (KCSAN) --
> > > > https://github.com/google/ktsan/wiki/KCSAN  (Details:
> > > > https://github.com/google/ktsan/blob/kcsan/Documentation/dev-tools/kcsan.rst)
> > > >
> > > > To those of you who we mentioned at LPC that we're working on a
> > > > watchpoint-based KTSAN inspired by DataCollider [1], this is it (we
> > > > renamed it to KCSAN to avoid confusion with KTSAN).
> > > > [1] http://usenix.org/legacy/events/osdi10/tech/full_papers/Erickson.pdf
> > > >
> > > > In the coming weeks we're planning to:
> > > > * Set up a syzkaller instance.
> > > > * Share the dashboard so that you can see the races that are found.
> > > > * Attempt to send fixes for some races upstream (if you find that the
> > > > kcsan-with-fixes branch contains an important fix, please feel free to
> > > > point it out and we'll prioritize that).
> > > >
> > > > There are a few open questions:
> > > > * The big one: most of the reported races are due to unmarked
> > > > accesses; prioritization or pruning of races to focus initial efforts
> > > > to fix races might be required. Comments on how best to proceed are
> > > > welcome. We're aware that these are issues that have recently received
> > > > attention in the context of the LKMM
> > > > (https://lwn.net/Articles/793253/).
> > > > * How/when to upstream KCSAN?
> > >
> > > Looks exciting. I think based on our discussion at LPC, you mentioned
> > > one way of pruning is if the compiler generated different code with _ONCE
> > > annotations than what would have otherwise been generated. Is that still on
> > > the table, for the purposing of pruning the reports?
> >
> > This might be interesting at first, but it's not entirely clear how
> > feasible it is. It's also dangerous, because the real issue would be
> > ignored. It may be that one compiler version on a particular
> > architecture generates the same code, but any change in compiler or
> > architecture and this would no longer be true. Let me know if you have
> > any more ideas.
> >
> > Best,
> > -- Marco
> >
> > > Also appreciate a CC on future patches as well.
> > >
> > > thanks,
> > >
> > >  - Joel
> > >
> > >
> > > >
> > > > Feel free to test and send feedback.
>
> FYI https://twitter.com/grsecurity/status/1179736828880048128 :)

+Christian opts in for _all_ reports for
kernel/{fork,exit,pid,signal}.c and friends.
Just wanted it to be written down for future reference :)