Subject: Re: [PATCH ipsec-next 4/6] xfrm: add TX datapath support for IPsec full offload mode

From: Leon Romanovsky <[email-masked]>
Date: Tue, 24 May 2022 21:30:28 +0300

On Wed, May 18, 2022 at 09:49:14AM +0200, Steffen Klassert wrote:
> On Mon, May 16, 2022 at 08:44:58AM +0300, Leon Romanovsky wrote:
> > On Fri, May 13, 2022 at 04:56:58PM +0200, Steffen Klassert wrote:
> > > On Tue, May 10, 2022 at 01:36:55PM +0300, Leon Romanovsky wrote:
> > > > From: Leon Romanovsky <[email-masked]>
> > > > 
> > > > In IPsec full mode, the device is going to encrypt and encapsulate
> > > > packets that are associated with offloaded policy. After successful
> > > > policy lookup to indicate if packets should be offloaded or not,
> > > > the stack forwards packets to the device to do the magic.
> > > > 
> > > > Signed-off-by: Raed Salem <[email-masked]>
> > > > Signed-off-by: Huy Nguyen <[email-masked]>
> > > > Signed-off-by: Leon Romanovsky <[email-masked]>
> > > > ---
> > > >  net/xfrm/xfrm_output.c | 19 +++++++++++++++++++
> > > >  1 file changed, 19 insertions(+)
> > > > 
> > > > diff --git a/net/xfrm/xfrm_output.c b/net/xfrm/xfrm_output.c
> > > > index d4935b3b9983..2599f3dbac08 100644
> > > > --- a/net/xfrm/xfrm_output.c
> > > > +++ b/net/xfrm/xfrm_output.c
> > > > @@ -718,6 +718,25 @@ int xfrm_output(struct sock *sk, struct sk_buff *skb)
> > > >  		break;
> > > >  	}
> > > >  
> > > > +	if (x->xso.type == XFRM_DEV_OFFLOAD_FULL) {
> > > > +		struct dst_entry *dst = skb_dst_pop(skb);
> > > > +
> > > > +		if (!dst) {
> > > > +			XFRM_INC_STATS(net, LINUX_MIB_XFRMOUTERROR);
> > > > +			return -EHOSTUNREACH;
> > > > +		}
> > > > +
> > > > +		skb_dst_set(skb, dst);
> > > > +		err = skb_dst(skb)->ops->local_out(net, skb->sk, skb);
> > > > +		if (unlikely(err != 1))
> > > > +			return err;
> > > > +
> > > > +		if (!skb_dst(skb)->xfrm)
> > > > +			return dst_output(net, skb->sk, skb);
> > > > +
> > > > +		return 0;
> > > > +	}
> > > > +
> > > 
> > > How do we know that we send the packet really to a device that
> > > supports this type of offload? For crypto offload, we check that
> > > in xfrm_dev_offload_ok() and I think something similar is required
> > > here too.
> > 
> > I think that function is needed to make sure that we will have SW
> > fallback. It is not needed in full offload, anything that is not
> > supported/wrong should be dropped by HW.
> 
> Yes, but only if the final output device really supports this kind
> of offload. How can we be sure that this is the case? Packets can be
> rerouted etc. We need to make sure that the outgoing device supports
> full offload, and I think this check is missing somewhere.

I think that something like this is missing (on top of the original patch):

diff --git a/net/xfrm/xfrm_output.c b/net/xfrm/xfrm_output.c
index 2599f3dbac08..a41aef3e8903 100644
--- a/net/xfrm/xfrm_output.c
+++ b/net/xfrm/xfrm_output.c
@@ -726,6 +726,9 @@ int xfrm_output(struct sock *sk, struct sk_buff *skb)
                        return -EHOSTUNREACH;
                }

+               if (!xfrm_dev_offload_ok(skb, x))
+                       return -EOPNOTSUPP;
+
                skb_dst_set(skb, dst);
                err = skb_dst(skb)->ops->local_out(net, skb->sk, skb);
                if (unlikely(err != 1))
(END)