rtl8139: validate rx ring before receiving packets

Commit ff71f2e8cacefae99179993204172bc65e4303df prevent the possible
crash during initialization of linux driver by checking the operating
mode.This seems too strict as:

- the real card could still work in mode other than normal
- some buggy driver who does not set correct opmode after eeprom
 access

So, considering rx ring address were reset to zero (which could be
safely trated as an address not intened to DMA to), in order to
both letting old guest work and preventing the unexpected DMA to
guest, we can forbid packet receiving when rx ring address is zero.

Tested-by: Avi Kivity <avi@redhat.com>
Signed-off-by: Jason Wang <jasowang@redhat.com>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>

1 files changed, 12 insertions, 10 deletions

diff --git a/hw/rtl8139.c b/hw/rtl8139.c
index f6f144b525..7b150475f4 100644
--- a/hw/rtl8139.c
+++ b/hw/rtl8139.c
@@ -781,6 +781,13 @@ static inline dma_addr_t rtl8139_addr64(uint32_t low, uint32_t high)
 #endif
 }
 
+/* Workaround for buggy guest driver such as linux who allocates rx
+ * rings after the receiver were enabled. */
+static bool rtl8139_cp_rx_valid(RTL8139State *s)
+{
+    return !(s->RxRingAddrLO == 0 && s->RxRingAddrHI == 0);
+}
+
 static int rtl8139_can_receive(VLANClientState *nc)
 {
     RTL8139State *s = DO_UPCAST(NICState, nc, nc)->opaque;
@@ -791,11 +798,8 @@ static int rtl8139_can_receive(VLANClientState *nc)
       return 1;
     if (!rtl8139_receiver_enabled(s))
       return 1;
-    /* network/host communication happens only in normal mode */
-    if ((s->Cfg9346 & Chip9346_op_mask) != Cfg9346_Normal)
-	return 0;
 
-    if (rtl8139_cp_receiver_enabled(s)) {
+    if (rtl8139_cp_receiver_enabled(s) && rtl8139_cp_rx_valid(s)) {
         /* ??? Flow control not implemented in c+ mode.
            This is a hack to work around slirp deficiencies anyway.  */
         return 1;
@@ -836,12 +840,6 @@ static ssize_t rtl8139_do_receive(VLANClientState *nc, const uint8_t *buf, size_
         return -1;
     }
 
-    /* check whether we are in normal mode */
-    if ((s->Cfg9346 & Chip9346_op_mask) != Cfg9346_Normal) {
-        DPRINTF("not in normal op mode\n");
-        return -1;
-    }
-
     /* XXX: check this */
     if (s->RxConfig & AcceptAllPhys) {
         /* promiscuous: receive all */
@@ -946,6 +944,10 @@ static ssize_t rtl8139_do_receive(VLANClientState *nc, const uint8_t *buf, size_
 
     if (rtl8139_cp_receiver_enabled(s))
     {
+        if (!rtl8139_cp_rx_valid(s)) {
+            return size;
+        }
+
         DPRINTF("in C+ Rx mode ================\n");
 
         /* begin C+ receiver mode */