Re: Re: [PATCH v7 04/12] virtio-blk: Add validation for block size in config space

From: "Michael S. Tsirkin" <mst@redhat.com>
To: Yongji Xie <xieyongji@bytedance.com>
Cc: "Jens Axboe" <axboe@kernel.dk>,
	linux-kernel <linux-kernel@vger.kernel.org>,
	kvm <kvm@vger.kernel.org>, "Jonathan Corbet" <corbet@lwn.net>,
	"Mika Penttilä" <mika.penttila@nextfour.com>,
	netdev@vger.kernel.org, "Randy Dunlap" <rdunlap@infradead.org>,
	iommu@lists.linux-foundation.org,
	"Matthew Wilcox" <willy@infradead.org>,
	virtualization <virtualization@lists.linux-foundation.org>,
	"Christoph Hellwig" <hch@infradead.org>,
	"Christian Brauner" <christian.brauner@canonical.com>,
	bcrl@kvack.org, viro@zeniv.linux.org.uk,
	"Stefan Hajnoczi" <stefanha@redhat.com>,
	linux-fsdevel@vger.kernel.org, joro@8bytes.org,
	"Dan Carpenter" <dan.carpenter@oracle.com>
Subject: Re: Re: [PATCH v7 04/12] virtio-blk: Add validation for block size in config space
Date: Thu, 20 May 2021 01:43:25 -0400	[thread overview]
Message-ID: <20210520013921-mutt-send-email-mst@kernel.org> (raw)
In-Reply-To: <CACycT3veubBFCg9omxLDJJFP7B7QH8++Q+tKmb_M_hmNS45cmw@mail.gmail.com>

On Thu, May 20, 2021 at 01:25:16PM +0800, Yongji Xie wrote:
> On Wed, May 19, 2021 at 10:42 PM Dan Carpenter <dan.carpenter@oracle.com> wrote:
> >
> > On Wed, May 19, 2021 at 09:39:20PM +0800, Yongji Xie wrote:
> > > On Mon, May 17, 2021 at 5:56 PM Xie Yongji <xieyongji@bytedance.com> wrote:
> > > >
> > > > This ensures that we will not use an invalid block size
> > > > in config space (might come from an untrusted device).
> >
> > I looked at if I should add this as an untrusted function so that Smatch
> > could find these sorts of bugs but this is reading data from the host so
> > there has to be some level of trust...
> >
> 
> It would be great if Smatch could detect this case if possible. The
> data might be trusted in traditional VM cases. But now the data can be
> read from a userspace daemon when VDUSE is enabled.
> 
> > I should add some more untrusted data kvm functions to Smatch.  Right
> > now I only have kvm_register_read() and I've added kvm_read_guest_virt()
> > just now.
> >
> > > >
> > > > Signed-off-by: Xie Yongji <xieyongji@bytedance.com>
> > > > ---
> > > >  drivers/block/virtio_blk.c | 2 +-
> > > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > >
> > > > diff --git a/drivers/block/virtio_blk.c b/drivers/block/virtio_blk.c
> > > > index ebb4d3fe803f..c848aa36d49b 100644
> > > > --- a/drivers/block/virtio_blk.c
> > > > +++ b/drivers/block/virtio_blk.c
> > > > @@ -826,7 +826,7 @@ static int virtblk_probe(struct virtio_device *vdev)
> > > >         err = virtio_cread_feature(vdev, VIRTIO_BLK_F_BLK_SIZE,
> > > >                                    struct virtio_blk_config, blk_size,
> > > >                                    &blk_size);
> > > > -       if (!err)
> > > > +       if (!err && blk_size > 0 && blk_size <= max_size)
> > >
> > > The check here is incorrect. I will use PAGE_SIZE as the maximum
> > > boundary in the new version.
> >
> > What does this bug look like to the user?
> 
> The kernel will panic if the block size is larger than PAGE_SIZE.

Kernel panic at this point is par for the course IMHO.
Let's focus on eliminating data corruption for starters.

> > A minimum block size of 1 seems pretty crazy.  Surely the minimum should be > higher?
> >
> 
> Yes, 512 is better here.
> 
> Thanks,
> Yongji

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