Subject: Re: [net PATCH 1/2] net: dsa: qca8k: fix inband mgmt for big-endian systems

From: Christian Marangi <[email-masked]>
Date: Wed, 12 Oct 2022 14:59:17 +0200

On Wed, Oct 12, 2022 at 02:54:54PM +0200, Christian Marangi wrote:
> On Wed, Oct 12, 2022 at 02:42:16PM +0200, Andrew Lunn wrote:
> > On Mon, Oct 10, 2022 at 01:14:58PM +0200, Christian Marangi wrote:
> > > The header and the data of the skb for the inband mgmt requires
> > > to be in little-endian. This is problematic for big-endian system
> > > as the mgmt header is written in the cpu byte order.
> > > 
> > > Fix this by converting each value for the mgmt header and data to
> > > little-endian, and convert to cpu byte order the mgmt header and
> > > data sent by the switch.
> > > 
> > > Fixes: 5950c7c0a68c ("net: dsa: qca8k: add support for mgmt read/write in Ethernet packet")
> > > Tested-by: Pawel Dembicki <[email-masked]>
> > > Tested-by: Lech Perczak <[email-masked]>
> > > Signed-off-by: Christian Marangi <[email-masked]>
> > > Reviewed-by: Lech Perczak <[email-masked]>
> > > ---
> > >  drivers/net/dsa/qca/qca8k-8xxx.c | 63 ++++++++++++++++++++++++--------
> > >  include/linux/dsa/tag_qca.h      |  6 +--
> > >  2 files changed, 50 insertions(+), 19 deletions(-)
> > > 
> > > diff --git a/drivers/net/dsa/qca/qca8k-8xxx.c b/drivers/net/dsa/qca/qca8k-8xxx.c
> > > index 5669c92c93f7..4bb9b7eac68b 100644
> > > --- a/drivers/net/dsa/qca/qca8k-8xxx.c
> > > +++ b/drivers/net/dsa/qca/qca8k-8xxx.c
> > > @@ -137,27 +137,42 @@ static void qca8k_rw_reg_ack_handler(struct dsa_switch *ds, struct sk_buff *skb)
> > >  	struct qca8k_mgmt_eth_data *mgmt_eth_data;
> > >  	struct qca8k_priv *priv = ds->priv;
> > >  	struct qca_mgmt_ethhdr *mgmt_ethhdr;
> > > +	u32 command;
> > >  	u8 len, cmd;
> > > +	int i;
> > >  
> > >  	mgmt_ethhdr = (struct qca_mgmt_ethhdr *)skb_mac_header(skb);
> > >  	mgmt_eth_data = &priv->mgmt_eth_data;
> > >  
> > > -	cmd = FIELD_GET(QCA_HDR_MGMT_CMD, mgmt_ethhdr->command);
> > > -	len = FIELD_GET(QCA_HDR_MGMT_LENGTH, mgmt_ethhdr->command);
> > > +	command = le32_to_cpu(mgmt_ethhdr->command);
> > > +	cmd = FIELD_GET(QCA_HDR_MGMT_CMD, command);
> > > +	len = FIELD_GET(QCA_HDR_MGMT_LENGTH, command);
> > 
> > Humm...
> > 
> > This might have the same alignment issue as the second patch. In fact,
> > because the Ethernet header is 14 bytes in size, it is often
> > deliberately out of alignment by 2 bytes, so that the IP header is
> > aligned. You should probably be using get_unaligned_le32() when
> > accessing members of mgmt_ethhdr.
> > 
> > 	  Andrew
> 
> Should I replace everything to get_unaligned_le32? Or this is only
> needed for the mgmt_ethhdr as it's 12 bytes?
> 
> The skb data is all 32 bit contiguous stuff so it should be safe? Or
> should we treat that also as unalligned just to make sure?
> 
> Same question for patch 2. the rest of the mib in skb data are all 32 or
> 64 values contiguous so wonder if we just take extra care of the
> mgmt_ethhdr. 
> 

Also also... Should I use put_unalligned to fill the mgmt_ethhdr?

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