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a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1763458338; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version: content-transfer-encoding:content-transfer-encoding; bh=+L4nsluUkpJVtRYxdSU6smFDneQWUovA9pfDq6jKaa0=; b=Lx4+ktlsCUKWtl8Kv18/avcddvAy4AnSI2U24W8b+zLH7y0xO8yIyRl9HY1GNS2wvF3TuA zWYXDKYvA9n1AzWS2Ybq8TFq72FM8wOdPDD0rjCurBzPpDUCtICmvQSCQuwqoKEFRjqbsw hli2NllRqjum30awlXyvxY5O05YXJI0= X-MC-Unique: PoLpf0RpOk6EjV5GKJ7syw-1 X-Mimecast-MFC-AGG-ID: PoLpf0RpOk6EjV5GKJ7syw_1763458331 From: Thomas Huth To: qemu-s390x@nongnu.org, Christian Borntraeger , Halil Pasic , Eric Farman , Matthew Rosato Cc: qemu-devel@nongnu.org, David Hildenbrand , =?UTF-8?q?C=C3=A9dric=20Le=20Goater?= , Cornelia Huck Subject: [PATCH] hw/s390x: Fix a possible crash with passed-through virtio devices Date: Tue, 18 Nov 2025 10:32:04 +0100 Message-ID: <20251118093204.34324-1-thuth@redhat.com> MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Scanned-By: MIMEDefang 3.4.1 on 10.30.177.93 Received-SPF: pass (zohomail.com: domain of gnu.org designates 209.51.188.17 as permitted sender) client-ip=209.51.188.17; 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charset="utf-8" From: Thomas Huth Consider the following nested setup: An L1 host uses some virtio device (e.g. virtio-keyboard) for the L2 guest, and this L2 guest passes this device through to the L3 guest. Since the L3 guest sees a virtio device, it might send virtio notifications to the QEMU in L2 for that device. But since the QEMU in L2 defined this device as vfio-ccw, the function handle_virtio_ccw_notify() cannot handle this and crashes: It calls virtio_ccw_get_vdev() that casts sch->driver_data into a VirtioCcwDevice, but since "sch" belongs to a vfio-ccw device, that driver_data rather points to a CcwDevice instead. So as soon as QEMU tries to use some VirtioCcwDevice specific data from that device, we've lost. We must not take virtio notifications for such devices. Thus fix the issue by adding a check to the handle_virtio_ccw_notify() handler to refuse all devices that are not our own virtio devices. Signed-off-by: Thomas Huth --- hw/s390x/s390-hypercall.c | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/hw/s390x/s390-hypercall.c b/hw/s390x/s390-hypercall.c index ac1b08b2cd5..7bee63aac67 100644 --- a/hw/s390x/s390-hypercall.c +++ b/hw/s390x/s390-hypercall.c @@ -42,6 +42,18 @@ static int handle_virtio_ccw_notify(uint64_t subch_id, u= int64_t data) if (!sch || !css_subch_visible(sch)) { return -EINVAL; } + if (sch->id.cu_type !=3D VIRTIO_CCW_CU_TYPE) { + /* + * This might happen in nested setups: If the L1 host defined the + * L2 guest with a virtio device (e.g. virtio-keyboard), and the + * L2 guest passes this device through to the L3 guest, the L3 gue= st + * might send virtio notifications to the QEMU in L2 for that devi= ce. + * But since the QEMU in L2 defined this device as vfio-ccw, it's = not + * a VirtIODevice that we can handle here! + */ + warn_report_once("Got virtio notification for unsupported device!"= ); + return -EINVAL; + } =20 vdev =3D virtio_ccw_get_vdev(sch); if (vq_idx >=3D VIRTIO_QUEUE_MAX || !virtio_queue_get_num(vdev, vq_idx= )) { --=20 2.51.1