linux-kernel - Re: [syzbot] [virt?] KCSAN: data-race in virtqueue_disable_cb / vring

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: <CANpmjNN+3TwdxkvnFzzeQNOVXq-smqpi+xtkw0j+Pd-BGkrgFw@mail.gmail.com>
Date: Thu, 12 Sep 2024 15:48:32 +0200
From: Marco Elver <elver@...gle.com>
To: "Michael S. Tsirkin" <mst@...hat.com>
Cc: syzbot <syzbot+8a02104389c2e0ef5049@...kaller.appspotmail.com>, 
	eperezma@...hat.com, jasowang@...hat.com, linux-kernel@...r.kernel.org, 
	syzkaller-bugs@...glegroups.com, virtualization@...ts.linux.dev, 
	xuanzhuo@...ux.alibaba.com
Subject: Re: [syzbot] [virt?] KCSAN: data-race in virtqueue_disable_cb /
 vring_interrupt (4)

On Thu, 12 Sept 2024 at 13:03, Michael S. Tsirkin <mst@...hat.com> wrote:
>
> On Thu, Sep 12, 2024 at 01:11:21AM -0700, syzbot wrote:
> > Hello,
> >
> > syzbot found the following issue on:
> >
> > HEAD commit:    7c6a3a65ace7 minmax: reduce min/max macro expansion in ato..
> > git tree:       upstream
> > console output: https://syzkaller.appspot.com/x/log.txt?x=1608e49f980000
> > kernel config:  https://syzkaller.appspot.com/x/.config?x=1e7d02549be622b2
> > dashboard link: https://syzkaller.appspot.com/bug?extid=8a02104389c2e0ef5049
> > compiler:       Debian clang version 15.0.6, GNU ld (GNU Binutils for Debian) 2.40
> >
> > Unfortunately, I don't have any reproducer for this issue yet.
> >
> > Downloadable assets:
> > disk image: https://storage.googleapis.com/syzbot-assets/a1f7496fa21f/disk-7c6a3a65.raw.xz
> > vmlinux: https://storage.googleapis.com/syzbot-assets/f423739e51a9/vmlinux-7c6a3a65.xz
> > kernel image: https://storage.googleapis.com/syzbot-assets/b65a0f38cbd7/bzImage-7c6a3a65.xz
> >
> > IMPORTANT: if you fix the issue, please add the following tag to the commit:
> > Reported-by: syzbot+8a02104389c2e0ef5049@...kaller.appspotmail.com
> >
> > ==================================================================
> > BUG: KCSAN: data-race in virtqueue_disable_cb / vring_interrupt
> >
> > write to 0xffff88810285ef52 of 1 bytes by interrupt on cpu 0:
> >  vring_interrupt+0x12b/0x180 drivers/virtio/virtio_ring.c:2591
>
>
> Yes, it's racy!
>
> 2589:        /* Just a hint for performance: so it's ok that this can be racy! */
> 2590:        if (vq->event)
> 2591:            vq->event_triggered = true;
>
>
> Question: is there a way to annotate code to tell syzbot it's ok?

In this case, "if (data_race(vq->event))" might be the right choice.

This is a quick guide on which access primitive to use in concurrent
code: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/tools/memory-model/Documentation/access-marking.txt

Thanks,
-- Marco