linux-kernel - Re: upstream kernel crashes

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Message-ID: <1660718191.3631961-1-xuanzhuo@linux.alibaba.com>
Date:   Wed, 17 Aug 2022 14:36:31 +0800
From:   Xuan Zhuo <xuanzhuo@...ux.alibaba.com>
To:     Dmitry Vyukov <dvyukov@...gle.com>
Cc:     James.Bottomley@...senpartnership.com, andres@...razel.de,
        axboe@...nel.dk, c@...hat.com, davem@...emloft.net,
        edumazet@...gle.com, gregkh@...uxfoundation.org,
        jasowang@...hat.com, kuba@...nel.org, linux-kernel@...r.kernel.org,
        linux@...ck-us.net, martin.petersen@...cle.com,
        netdev@...r.kernel.org, pabeni@...hat.com,
        torvalds@...ux-foundation.org,
        virtualization@...ts.linux-foundation.org,
        kasan-dev@...glegroups.com, mst@...hat.com
Subject: Re: upstream kernel crashes

On Wed, 17 Aug 2022 08:13:59 +0200, Dmitry Vyukov <dvyukov@...gle.com> wrote:
> On Mon, 15 Aug 2022 17:32:06 -0400, Michael wrote:
> > So if you pass the size parameter for a legacy device it will
> > try to make the ring smaller and that is not legal with
> > legacy at all. But the driver treats legacy and modern
> > the same, it allocates a smaller queue anyway.
> >
> > Lo and behold, I pass disable-modern=on to qemu and it happily
> > corrupts memory exactly the same as GCP does.
>
> Ouch!
>
> I understand that the host does the actual corruption,
> but could you think of any additional debug checking in the guest
> that would caught this in future? Potentially only when KASAN
> is enabled which can verify validity of memory ranges.
> Some kind of additional layer of sanity checking.
>
> This caused a bit of a havoc for syzbot with almost 100 unique
> crash signatures, so would be useful to catch such issues more
> reliably in future.

We can add a check to vring size before calling vp_legacy_set_queue_address().
Checking the memory range directly is a bit cumbersome.

Thanks.

diff --git a/drivers/virtio/virtio_pci_legacy.c b/drivers/virtio/virtio_pci_legacy.c
index 2257f1b3d8ae..0673831f45b6 100644
--- a/drivers/virtio/virtio_pci_legacy.c
+++ b/drivers/virtio/virtio_pci_legacy.c
@@ -146,6 +146,8 @@ static struct virtqueue *setup_vq(struct virtio_pci_device *vp_dev,
                goto out_del_vq;
        }

+       BUG_ON(num != virtqueue_get_vring_size(vq));
+
        /* activate the queue */
        vp_legacy_set_queue_address(&vp_dev->ldev, index, q_pfn);


>
> Thanks