Message-ID: <CAKMK7uGNC0FmDs6XrFju+adSV0UcNcuZcGESqEq54LJWMEFQ9A@mail.gmail.com>
Date:   Tue, 31 Mar 2020 14:57:28 +0200
From:   Daniel Vetter <daniel@...ll.ch>
To:     Bartlomiej Zolnierkiewicz <b.zolnierkie@...sung.com>
Cc:     Dmitry Vyukov <dvyukov@...gle.com>,
        Linux Fbdev development list <linux-fbdev@...r.kernel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        syzbot <syzbot+e84d7ebd1361da13c356@...kaller.appspotmail.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        syzkaller-bugs <syzkaller-bugs@...glegroups.com>,
        LKML <linux-kernel@...r.kernel.org>,
        DRI <dri-devel@...ts.freedesktop.org>,
        Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: INFO: trying to register non-static key in try_to_wake_up

On Tue, Mar 31, 2020 at 2:50 PM Daniel Vetter <daniel@...ll.ch> wrote:
>
> On Tue, Mar 31, 2020 at 2:18 PM Bartlomiej Zolnierkiewicz
> <b.zolnierkie@...sung.com> wrote:
> >
> >
> > On 3/31/20 12:18 PM, Dmitry Vyukov wrote:
> > > On Tue, Mar 31, 2020 at 11:57 AM Peter Zijlstra <peterz@...radead.org> wrote:
> > >>
> > >> On Mon, Mar 30, 2020 at 10:01:12PM -0700, syzbot wrote:
> > >>> Hello,
> > >>>
> > >>> syzbot found the following crash on:
> > >>>
> > >>> HEAD commit:    9420e8ad Merge tag 'for-linus' of git://git.kernel.org/pub..
> > >>> git tree:       upstream
> > >>> console output: https://protect2.fireeye.com/url?k=0756a78d-5a9a6c49-07572cc2-0cc47a314e9a-e4dc8b657d340686&u=https://syzkaller.appspot.com/x/log.txt?x=1206ed4be00000
> > >>> kernel config:  https://protect2.fireeye.com/url?k=43211072-1eeddbb6-43209b3d-0cc47a314e9a-3bd45a19932c37c8&u=https://syzkaller.appspot.com/x/.config?x=27392dd2975fd692
> > >>> dashboard link: https://protect2.fireeye.com/url?k=bf7a6153-e2b6aa97-bf7bea1c-0cc47a314e9a-c64073ee605efb7b&u=https://syzkaller.appspot.com/bug?extid=e84d7ebd1361da13c356
> > >>> compiler:       gcc (GCC) 9.0.0 20181231 (experimental)
> > >>>
> > >>> Unfortunately, I don't have any reproducer for this crash yet.
> > >>>
> > >>> IMPORTANT: if you fix the bug, please add the following tag to the commit:
> > >>> Reported-by: syzbot+e84d7ebd1361da13c356@...kaller.appspotmail.com
> > >>>
> > >>> INFO: trying to register non-static key.
> > >>> the code is fine but needs lockdep annotation.
> > >>> turning off the locking correctness validator.
> > >>> CPU: 1 PID: 1014 Comm: syz-executor.0 Not tainted 5.6.0-rc7-syzkaller #0
> > >>> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> > >>> Call Trace:
> > >>>  <IRQ>
> > >>>  __dump_stack lib/dump_stack.c:77 [inline]
> > >>>  dump_stack+0x188/0x20d lib/dump_stack.c:118
> > >>>  assign_lock_key kernel/locking/lockdep.c:880 [inline]
> > >>>  register_lock_class+0x14c4/0x1540 kernel/locking/lockdep.c:1189
> > >>>  __lock_acquire+0xfc/0x3ca0 kernel/locking/lockdep.c:3836
> > >>>  lock_acquire+0x197/0x420 kernel/locking/lockdep.c:4484
> > >>>  __raw_spin_lock_irqsave include/linux/spinlock_api_smp.h:110 [inline]
> > >>>  _raw_spin_lock_irqsave+0x8c/0xbf kernel/locking/spinlock.c:159
> > >>>  try_to_wake_up+0x9f/0x17c0 kernel/sched/core.c:2547
> > >>
> > >> That's p->pi_lock, which gets initialized in rt_mutex_init_task() in
> > >> copy_process(). This should be impossible. Very odd.
> > >
> > > The stack mentions fbdev, which is a red flag at the moment. There are
> > > a dozen of bad bugs in fbdev and around. Just few days ago Andy
> > > pointed to another "impossible" crash "general protection fault in
> > > do_syscall_64" which is related to dri:
> > > https://protect2.fireeye.com/url?k=0cb8ad06-517466c2-0cb92649-0cc47a314e9a-a20c11191483c65b&u=https://syzkaller.appspot.com/bug?id=0ec7b2602b1ff40f0d34f38baa4ba1640727c3d9
> > > https://protect2.fireeye.com/url?k=614292e3-3c8e5927-614319ac-0cc47a314e9a-aeda6d72c01a7b0e&u=https://groups.google.com/forum/#!msg/syzkaller-bugs/ePqhfYx0-8M/Q_Urt97iAAAJ
> > >
> > > There are probably more random manifestations of these bugs already,
> > > and I guess we will be getting more.
> > >
> > > +fbdev maintainers
> >
> > Thank you for the report.
> >
> > fbdev is in the maintenance mode and no new features or drivers are
> > being added so syzbot reports are not for a new bugs (regressions) and
> > are not a priority (at least to me).
>
> Yup same here, I've seen a pile of syzbot reports for fbdev (and also
> vt, or combinations of them since fbdev is linked to vt through fbcon)
> fly by. But I really don't have to deal with these, my recommendation
> to anyone who cares about security are:
> - Don't enable vt
> - Don't enable fbdev
>
> All that code has been developed long ago, in a much more innocent
> time. If someone wants to fix this you'd not just need to fix all the
> syzbot stuff, but also ramp up a full testsuite for all the ioctl, and
> all the corner-cases. Plus also fix some of the horrendous locking in
> there, probably.
>
> Multi-year effort, easily.
>
> Regressions I'll obviously try to handle, but none of these are. It's
> just syzbot has become smarter at hitting bugs in fbdev and vt
> subsystems (or maybe the hw the virtual machines emulate has become
> more varied, some of the reports are for fun stuff like vgacon ...).

Forgot to mention: Just yesterday I did merge an fbcon overflow bugfix:
commit b139f8b00db4a8ea75a4174346eafa48041aa489 (HEAD ->
drm-misc-next-fixes, drm-misc/for-linux-next,
drm-misc/drm-misc-next-fixes)
Author: Qiujun Huang <hqjagain@...il.com>
Date:   Sun Mar 29 16:56:47 2020 +0800

    fbcon: fix null-ptr-deref in fbcon_switch

There's also a pending patch in the vt subsystem to catch overflow for
unicode fonts on consoles, that's reviewed and waiting for Greg to
pick it up.
-Daniel

> Cheers, Daniel
>
> > I have only resources to review/merge pending fbdev patches from time
> > to time so any help in fixing these syzbot reports is welcomed (there
> > have been a few fbdev related syzbot reports recently).
> >
> > Also please note that fbdev is maintained through drm-misc tree so
> > patches can also be handled by other drm-misc maintainers in case I'm
> > not available / busy with other things.
> >
> > Best regards,
> > --
> > Bartlomiej Zolnierkiewicz
> > Samsung R&D Institute Poland
> > Samsung Electronics
> >
> > >>>  wake_up_worker kernel/workqueue.c:836 [inline]
> > >>>  insert_work+0x2ad/0x3a0 kernel/workqueue.c:1337
> > >>>  __queue_work+0x50d/0x1280 kernel/workqueue.c:1488
> > >>>  call_timer_fn+0x195/0x760 kernel/time/timer.c:1404
> > >>>  expire_timers kernel/time/timer.c:1444 [inline]
> > >>>  __run_timers kernel/time/timer.c:1773 [inline]
> > >>>  __run_timers kernel/time/timer.c:1740 [inline]
> > >>>  run_timer_softirq+0x412/0x1600 kernel/time/timer.c:1786
> > >>>  __do_softirq+0x26c/0x99d kernel/softirq.c:292
> > >>>  invoke_softirq kernel/softirq.c:373 [inline]
> > >>>  irq_exit+0x192/0x1d0 kernel/softirq.c:413
> > >>>  exiting_irq arch/x86/include/asm/apic.h:546 [inline]
> > >>>  smp_apic_timer_interrupt+0x19e/0x600 arch/x86/kernel/apic/apic.c:1146
> > >>>  apic_timer_interrupt+0xf/0x20 arch/x86/entry/entry_64.S:829
> > >>>  </IRQ>
> > _______________________________________________
> > dri-devel mailing list
> > dri-devel@...ts.freedesktop.org
> > https://lists.freedesktop.org/mailman/listinfo/dri-devel
>
>
>
> --
> Daniel Vetter
> Software Engineer, Intel Corporation
> +41 (0) 79 365 57 48 - http://blog.ffwll.ch



-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch

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