netdev - Re: [PATCH bpf-next v4 12/21] xdp: Add checksum hint

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <ZNEOf3vTu6pmNG1J@lincoln>
Date: Mon, 7 Aug 2023 17:32:15 +0200
From: Larysa Zaremba <larysa.zaremba@...el.com>
To: Alexei Starovoitov <alexei.starovoitov@...il.com>, Jesper Dangaard Brouer
	<hawk@...nel.org>, Stanislav Fomichev <sdf@...gle.com>
CC: Willem de Bruijn <willemdebruijn.kernel@...il.com>, bpf
	<bpf@...r.kernel.org>, Alexei Starovoitov <ast@...nel.org>, Daniel Borkmann
	<daniel@...earbox.net>, Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau
	<martin.lau@...ux.dev>, Song Liu <song@...nel.org>, Yonghong Song
	<yhs@...com>, John Fastabend <john.fastabend@...il.com>, KP Singh
	<kpsingh@...nel.org>, Stanislav Fomichev <sdf@...gle.com>, Hao Luo
	<haoluo@...gle.com>, Jiri Olsa <jolsa@...nel.org>, David Ahern
	<dsahern@...il.com>, Jakub Kicinski <kuba@...nel.org>, Willem de Bruijn
	<willemb@...gle.com>, Jesper Dangaard Brouer <brouer@...hat.com>, "Anatoly
 Burakov" <anatoly.burakov@...el.com>, Alexander Lobakin
	<alexandr.lobakin@...el.com>, Magnus Karlsson <magnus.karlsson@...il.com>,
	Maryam Tahhan <mtahhan@...hat.com>, <xdp-hints@...-project.net>, "Network
 Development" <netdev@...r.kernel.org>, Simon Horman
	<simon.horman@...igine.com>
Subject: Re: [PATCH bpf-next v4 12/21] xdp: Add checksum hint

On Mon, Jul 31, 2023 at 06:03:26PM -0700, Alexei Starovoitov wrote:
> On Mon, Jul 31, 2023 at 3:56 AM Larysa Zaremba <larysa.zaremba@...el.com> wrote:
> >
> > On Sun, Jul 30, 2023 at 09:13:02AM -0400, Willem de Bruijn wrote:
> > > Alexei Starovoitov wrote:
> > > > On Sat, Jul 29, 2023 at 9:15 AM Willem de Bruijn
> > > > <willemdebruijn.kernel@...il.com> wrote:
> > > > >
> > > > > Alexei Starovoitov wrote:
> > > > > > On Fri, Jul 28, 2023 at 07:39:14PM +0200, Larysa Zaremba wrote:
> > > > > > >
> > > > > > > +union xdp_csum_info {
> > > > > > > +   /* Checksum referred to by ``csum_start + csum_offset`` is considered
> > > > > > > +    * valid, but was never calculated, TX device has to do this,
> > > > > > > +    * starting from csum_start packet byte.
> > > > > > > +    * Any preceding checksums are also considered valid.
> > > > > > > +    * Available, if ``status == XDP_CHECKSUM_PARTIAL``.
> > > > > > > +    */
> > > > > > > +   struct {
> > > > > > > +           u16 csum_start;
> > > > > > > +           u16 csum_offset;
> > > > > > > +   };
> > > > > > > +
> > > > > >
> > > > > > CHECKSUM_PARTIAL makes sense on TX, but this RX. I don't see in the above.
> > > > >
> > > > > It can be observed on RX when packets are looped.
> > > > >
> > > > > This may be observed even in XDP on veth.
> > > >
> > > > veth and XDP is a broken combination. GSO packets coming out of containers
> > > > cannot be parsed properly by XDP.
> > > > It was added mainly for testing. Just like "generic XDP".
> > > > bpf progs at skb layer is much better fit for veth.
> > >
> > > Ok. Still, seems forward looking and little cost to define the
> > > constant?
> > >
> >
> > +1
> > CHECKSUM_PARTIAL is mostly for testing and removing/adding it doesn't change
> > anything from the perspective of the user that does not use it, so I think it is
> > worth having.
> 
> "little cost to define the constant".
> Not really. A constant in UAPI is a heavy burden.

Sorry for the delayed response.

I still do not comprehend the problem fully for this particular case, 
considering it shouldn't block any future changes to the API by itself.

But, I personally have no reason to push hard the veth-supporting changes 
(aside from wanting the tests to look nicer).

Still, before removing this in v5, I would like to get some additional feedback 
on this, preferably from Jesper (who, if I remember correctly, takes an interest 
in XDP on veth) or Stanislav.

If instead of union xdp_csum_info we will have just checksum as a second 
argument, there will be no going back for this particular kfunc, so I want to be 
sure nobody will ever need such feature.

[...]