Subject: Re: [PATCH net v5] net: stmmac: Prevent DSA tags from breaking COE

From: Jakub Kicinski <[email-masked]>
Date: Tue, 16 Jan 2024 07:23:00 -0800

On Tue, 16 Jan 2024 13:14:15 +0100 (CET) Romain Gantois wrote:
> > > @@ -4997,7 +5020,7 @@ static void stmmac_dispatch_skb_zc(struct stmmac_priv *priv, u32 queue,
> > >  	stmmac_rx_vlan(priv->dev, skb);
> > >  	skb->protocol = eth_type_trans(skb, priv->dev);
> > >  
> > > -	if (unlikely(!coe))
> > > +	if (unlikely(!coe) || !stmmac_has_ip_ethertype(skb))  
> > 
> > The lack of Rx side COE checking in this driver is kinda crazy.
> > Looking at enh_desc_coe_rdes0() it seems like RDES0_FRAME_TYPE
> > may be the indication we need here?   
> 
> I don't think that RDES0_FRAME_TYPE would be enough, at least not on its own. 
> That bit is set by checking the length/ethertype field to see if is an 
> Ethernet II frame or an IEEE802.3 frame. But even Ethernet II frames with non-IP 
> ethertypes will not be checksummed. Also protocols with a non-fixed ethertype 
> field such as DSA_TAG_PROTO could trigger the bit, or not, depending on what 
> they put in the DSA tag.

Hm, the comment in enh_desc_coe_rdes0() says:

	/* bits 5 7 0 | Frame status
	 * ----------------------------------------------------------
	 *      0 0 0 | IEEE 802.3 Type frame (length < 1536 octects)
	 *      1 0 0 | IPv4/6 No CSUM errorS.
	 *      1 0 1 | IPv4/6 CSUM PAYLOAD error
	 *      1 1 0 | IPv4/6 CSUM IP HR error
	 *      1 1 1 | IPv4/6 IP PAYLOAD AND HEADER errorS
	 *      0 0 1 | IPv4/6 unsupported IP PAYLOAD
	 *      0 1 1 | COE bypassed.. no IPv4/6 frame
	 *      0 1 0 | Reserved.
	 */

which makes it sound like bit 5 will not be set for a Ethernet II frame
with unsupported IP payload, or not an IP frame. Does the bit mean other
things in different descriptor formats?