fix: machyve#164 virtio-net + UEFI crash

When using virtio-net with an UEFI firmware (bootrom), xhyve crashes on an assertion. See the related bug machyve#164 The complete details are not clear to me, but it seems that during boot, the firmware reads on the interface but doesn't provide big enough read buffers. It seems that the space for VLAN headers is missing. This patch drops the related reads, so normal booting can occur. Network boot probably doesn't work, though. Signed-off-by: Antoine Martin [email protected]
skunkwerks · Oct 17, 2020 · d1ce163 · d1ce163
1 parent 2368a7a
commit d1ce163
Showing 1 changed file with 29 additions and 11 deletions.
diff --git a/src/pci_virtio_net_vmnet.c b/src/pci_virtio_net_vmnet.c
@@ -334,7 +334,10 @@ vmn_read(struct vmnet_state *vms, struct iovec *iov, int n) {
 		v.vm_pkt_size += iov[i].iov_len;
 	}
 
-	assert(v.vm_pkt_size >= vms->max_packet_size);
+	if (v.vm_pkt_size < vms->max_packet_size) {
+			fprintf(stderr, "Read buffer too small: %ld bytes. vmnet expected at least %d.\n", v.vm_pkt_size, vms->max_packet_size);
+			return (-2);
+	}
 
 	v.vm_pkt_iov = iov;
 	v.vm_pkt_iovcnt = (uint32_t) n;
@@ -550,17 +553,32 @@ pci_vtnet_tap_rx(struct pci_vtnet_softc *sc)
 		 */
 		vrx = iov[0].iov_base;
 		riov = rx_iov_trim(iov, &n, sc->rx_vhdrlen);
-
+        
 		len = (int) vmn_read(sc->vms, riov, n);
-
-		if (len < 0 && errno == EWOULDBLOCK) {
-			/*
-			 * No more packets, but still some avail ring
-			 * entries.  Interrupt if needed/appropriate.
-			 */
-			vq_retchain(vq);
-			vq_endchains(vq, 0);
-			return;
+
+		if (len < 0) {
+			if (len == -2) {
+					/*
+						* Buffer passed is too short. The reason is unclear
+						* to me but it seems that at boot some firmwares pass
+						* buffers of the standard 1514 Ethernet length whereas the
+						* size expected by Mac OS is 1518.
+						*/
+					iov[0].iov_base = dummybuf;
+					iov[0].iov_len = sizeof(dummybuf);
+					(void) vmn_read(sc->vms, iov, 1);
+					vq_endchains(vq, 1);
+					return;
+
+			} else if (errno == EWOULDBLOCK) {
+					/*
+						* No more packets, but still some avail ring
+						* entries.  Interrupt if needed/appropriate.
+						*/
+					vq_retchain(vq);
+					vq_endchains(vq, 0);
+					return;
+			}
 		}
 
 		/*