[PATCH] hw/net: fsl_etsec: Do not reject short frames

[PATCH] hw/net: fsl_etsec: Do not reject short frames

[Bin Meng]

As of today both slirp and tap networking do not pad short frames
(e.g.: an ARP packet) to the minimum frame size of 60 bytes.

If eTSEC is programmed to reject short frames, ARP requests will be
dropped, preventing the guest from becoming visible on the network.

The same issue was reported on e1000 and vmxenet3 before, see:

commit 78aeb23eded2 ("e1000: Pad short frames to minimum size (60 bytes)")
commit 40a87c6c9b11 ("vmxnet3: Pad short frames to minimum size (60 bytes)")

Ideally this should be fixed on the slirp/tap networking side to
pad short frames to the minimum frame length, but I am not sure
whether that's doable.

This commit changes to codes to ignore the RCTRL_RSF setting and
still allow receiving the short frame. The log message is updated
to mention the reject short frames functionality is unimplemented.

Signed-off-by: Bin Meng <bin.meng@windriver.com>
---

 hw/net/fsl_etsec/rings.c | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/hw/net/fsl_etsec/rings.c b/hw/net/fsl_etsec/rings.c
index 121415a..503b4d3 100644
--- a/hw/net/fsl_etsec/rings.c
+++ b/hw/net/fsl_etsec/rings.c
@@ -502,10 +502,17 @@ ssize_t etsec_rx_ring_write(eTSEC *etsec, const uint8_t *buf, size_t size)
         return -1;
     }
 
+    /*
+     * Both slirp and tap networking do not pad short frames
+     * (e.g.: an ARP packet) to the minimum frame size of 60 bytes.
+     *
+     * If eTSEC is programmed to reject short frames, ARP requests
+     * will be dropped, preventing the guest from becoming visible
+     * on the network.
+     */
     if ((etsec->regs[RCTRL].value & RCTRL_RSF) && (size < 60)) {
         /* CRC is not in the packet yet, so short frame is below 60 bytes */
-        RING_DEBUG("%s: Drop short frame\n", __func__);
-        return -1;
+        RING_DEBUG("%s: Drop short frame not implemented\n", __func__);
     }
 
     rx_init_frame(etsec, buf, size);
-- 
2.7.4

Re: [PATCH] hw/net: fsl_etsec: Do not reject short frames

[Philippe Mathieu-Daudé]

Cc'ing libSLiRP.

On 2/8/21 7:41 AM, Bin Meng wrote:
> As of today both slirp and tap networking do not pad short frames
> (e.g.: an ARP packet) to the minimum frame size of 60 bytes.
> 
> If eTSEC is programmed to reject short frames, ARP requests will be
> dropped, preventing the guest from becoming visible on the network.
> 
> The same issue was reported on e1000 and vmxenet3 before, see:
> 
> commit 78aeb23eded2 ("e1000: Pad short frames to minimum size (60 bytes)")
> commit 40a87c6c9b11 ("vmxnet3: Pad short frames to minimum size (60 bytes)")
> 
> Ideally this should be fixed on the slirp/tap networking side to
> pad short frames to the minimum frame length, but I am not sure
> whether that's doable.
> 
> This commit changes to codes to ignore the RCTRL_RSF setting and
> still allow receiving the short frame. The log message is updated
> to mention the reject short frames functionality is unimplemented.
> 
> Signed-off-by: Bin Meng <bin.meng@windriver.com>
> ---
> 
>  hw/net/fsl_etsec/rings.c | 11 +++++++++--
>  1 file changed, 9 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/net/fsl_etsec/rings.c b/hw/net/fsl_etsec/rings.c
> index 121415a..503b4d3 100644
> --- a/hw/net/fsl_etsec/rings.c
> +++ b/hw/net/fsl_etsec/rings.c
> @@ -502,10 +502,17 @@ ssize_t etsec_rx_ring_write(eTSEC *etsec, const uint8_t *buf, size_t size)
>          return -1;
>      }
>  
> +    /*
> +     * Both slirp and tap networking do not pad short frames
> +     * (e.g.: an ARP packet) to the minimum frame size of 60 bytes.
> +     *
> +     * If eTSEC is programmed to reject short frames, ARP requests
> +     * will be dropped, preventing the guest from becoming visible
> +     * on the network.
> +     */
>      if ((etsec->regs[RCTRL].value & RCTRL_RSF) && (size < 60)) {
>          /* CRC is not in the packet yet, so short frame is below 60 bytes */
> -        RING_DEBUG("%s: Drop short frame\n", __func__);
> -        return -1;
> +        RING_DEBUG("%s: Drop short frame not implemented\n", __func__);
>      }
>  
>      rx_init_frame(etsec, buf, size);
>