linux-kernel - Re: WARNING: suspicious RCU usage in idtentry

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <CACT4Y+bVPSZVkWJquu5gk11ymhirsFvVFYHkexjqgBkgga379w@mail.gmail.com>
Date:   Fri, 29 May 2020 08:20:12 +0200
From:   Dmitry Vyukov <dvyukov@...gle.com>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        syzbot <syzbot+3ae5eaae0809ee311e75@...kaller.appspotmail.com>,
        Paolo Bonzini <pbonzini@...hat.com>,
        Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Andy Lutomirski <luto@...nel.org>,
        Ingo Molnar <mingo@...nel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        "the arch/x86 maintainers" <x86@...nel.org>
Subject: Re: WARNING: suspicious RCU usage in idtentry_exit

On Thu, May 28, 2020 at 10:48 PM Paul E. McKenney <paulmck@...nel.org> wrote:
>
> On Thu, May 28, 2020 at 10:19:02PM +0200, Thomas Gleixner wrote:
> > Paul,
> >
> > "Paul E. McKenney" <paulmck@...nel.org> writes:
> > > On Thu, May 28, 2020 at 03:33:44PM +0200, Thomas Gleixner wrote:
> > >> syzbot <syzbot+3ae5eaae0809ee311e75@...kaller.appspotmail.com> writes:
> > >> Weird. I have no idea how that thing is an EQS here.
> > >
> > > No argument on the "Weird" part!  ;-)
> > >
> > > Is this a NO_HZ_FULL=y kernel?
> >
> > No, it has only NO_HZ_IDLE.
> >
> >   https://syzkaller.appspot.com/x/.config?x=47b0740d89299c10
>
> OK, from the .config, another suggestion is to build the kernel
> with CONFIG_RCU_EQS_DEBUG=y.  This still requires that this issue be
> reproduced, but it might catch the problem earlier.

How much does it slow down execution? If we enable it on syzbot, it
will affect all fuzzing done by syzbot always.
It can tolerate significant slowdown and it's far from a production
kernel (it enables KASAN, KCOV, LOCKDEP and more). But I am still
asking because some debugging features are built without performance
in mind at all (like let's just drop a global lock in every
kmalloc/free, which may be too much even for a standard debug build).


> > > If so, one possibility is that the call
> > > to rcu_user_exit() went missing somehow.  If not, then RCU should have
> > > been watching userspace execution.
> > >
> > > Again, the only thing I can think of (should this prove to be
> > > reproducible) is the rcu_dyntick trace event.
> >
> > :)
> >
> > Thanks,
> >
> >         tglx
>
>                                                         Thanx, Paul
>
> --
> You received this message because you are subscribed to the Google Groups "syzkaller-bugs" group.
> To unsubscribe from this group and stop receiving emails from it, send an email to syzkaller-bugs+unsubscribe@...glegroups.com.
> To view this discussion on the web visit https://groups.google.com/d/msgid/syzkaller-bugs/20200528204839.GR2869%40paulmck-ThinkPad-P72.