e1000: Pad short frames to minimum size (60 bytes)

The OpenIndiana (Solaris) e1000g driver drops frames that are too long
or too short.  It expects to receive frames of at least the Ethernet
minimum size.  ARP requests in particular are small and will be dropped
if they are not padded appropriately, preventing a Solaris VM from
becoming visible on the network.
Signed-off-by: NStefan Hajnoczi <stefanha@linux.vnet.ibm.com>
Signed-off-by: NMichael S. Tsirkin <mst@redhat.com>

hw/e1000.c

@@ -55,6 +55,7 @@ static int debugflags = DBGBIT(TXERR) | DBGBIT(GENERAL);
 
 #define IOPORT_SIZE       0x40
 #define PNPMMIO_SIZE      0x20000
+#define MIN_BUF_SIZE      60 /* Min. octets in an ethernet frame sans FCS */
 
 /*
  * HW models:
@@ -635,10 +636,19 @@ e1000_receive(VLANClientState *nc, const uint8_t *buf, size_t size)
     uint32_t rdh_start;
     uint16_t vlan_special = 0;
     uint8_t vlan_status = 0, vlan_offset = 0;
+    uint8_t min_buf[MIN_BUF_SIZE];
 
     if (!(s->mac_reg[RCTL] & E1000_RCTL_EN))
         return -1;
 
+    /* Pad to minimum Ethernet frame length */
+    if (size < sizeof(min_buf)) {
+        memcpy(min_buf, buf, size);
+        memset(&min_buf[size], 0, sizeof(min_buf) - size);
+        buf = min_buf;
+        size = sizeof(min_buf);
+    }
+
     if (size > s->rxbuf_size) {
         DBGOUT(RX, "packet too large for buffers (%lu > %d)\n",
                (unsigned long)size, s->rxbuf_size);