netdev - Re: [PATCH RFC bpf-next v2 1/5] netlink: specs: Add XDP RX checksum capability to XDP metadata specs

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: <e03d6d69-73ea-46dc-b632-149ef5831f85@kernel.org>
Date: Fri, 26 Sep 2025 10:59:51 +0200
From: Jesper Dangaard Brouer <hawk@...nel.org>
To: Stanislav Fomichev <stfomichev@...il.com>,
 Lorenzo Bianconi <lorenzo@...nel.org>
Cc: Donald Hunter <donald.hunter@...il.com>, Jakub Kicinski
 <kuba@...nel.org>, "David S. Miller" <davem@...emloft.net>,
 Eric Dumazet <edumazet@...gle.com>, Paolo Abeni <pabeni@...hat.com>,
 Simon Horman <horms@...nel.org>, Alexei Starovoitov <ast@...nel.org>,
 Daniel Borkmann <daniel@...earbox.net>,
 John Fastabend <john.fastabend@...il.com>,
 Stanislav Fomichev <sdf@...ichev.me>, Andrew Lunn <andrew+netdev@...n.ch>,
 Tony Nguyen <anthony.l.nguyen@...el.com>,
 Przemek Kitszel <przemyslaw.kitszel@...el.com>,
 Alexander Lobakin <aleksander.lobakin@...el.com>,
 Andrii Nakryiko <andrii@...nel.org>, Martin KaFai Lau
 <martin.lau@...ux.dev>, Eduard Zingerman <eddyz87@...il.com>,
 Song Liu <song@...nel.org>, Yonghong Song <yonghong.song@...ux.dev>,
 KP Singh <kpsingh@...nel.org>, Hao Luo <haoluo@...gle.com>,
 Jiri Olsa <jolsa@...nel.org>, Shuah Khan <shuah@...nel.org>,
 Maciej Fijalkowski <maciej.fijalkowski@...el.com>, netdev@...r.kernel.org,
 bpf@...r.kernel.org, intel-wired-lan@...ts.osuosl.org,
 linux-kselftest@...r.kernel.org
Subject: Re: [PATCH RFC bpf-next v2 1/5] netlink: specs: Add XDP RX checksum
 capability to XDP metadata specs

On 26/09/2025 06.20, Stanislav Fomichev wrote:
> On 09/25, Lorenzo Bianconi wrote:
>> Introduce XDP RX checksum capability to XDP metadata specs. XDP RX
>> checksum will be use by devices capable of exposing receive checksum
>> result via bpf_xdp_metadata_rx_checksum().
>> Moreover, introduce xmo_rx_checksum netdev callback in order allow the
>> eBPF program bounded to the device to retrieve the RX checksum result
>> computed by the hw NIC.
>>
>> Signed-off-by: Lorenzo Bianconi <lorenzo@...nel.org>
>> ---
>>   Documentation/netlink/specs/netdev.yaml |  5 +++++
>>   include/net/xdp.h                       | 14 ++++++++++++++
>>   net/core/xdp.c                          | 29 +++++++++++++++++++++++++++++
>>   3 files changed, 48 insertions(+)
>>
>> diff --git a/Documentation/netlink/specs/netdev.yaml b/Documentation/netlink/specs/netdev.yaml
>> index e00d3fa1c152d7165e9485d6d383a2cc9cef7cfd..00699bf4a7fdb67c6b9ee3548098b0c933fd39a4 100644
>> --- a/Documentation/netlink/specs/netdev.yaml
>> +++ b/Documentation/netlink/specs/netdev.yaml
>> @@ -61,6 +61,11 @@ definitions:
>>           doc: |
>>             Device is capable of exposing receive packet VLAN tag via
>>             bpf_xdp_metadata_rx_vlan_tag().
>> +      -
>> +        name: checksum
>> +        doc: |
>> +          Device is capable of exposing receive checksum result via
>> +          bpf_xdp_metadata_rx_checksum().
>>     -
>>       type: flags
>>       name: xsk-flags
>> diff --git a/include/net/xdp.h b/include/net/xdp.h
>> index aa742f413c358575396530879af4570dc3fc18de..9ab9ac10ae2074b70618a9d4f32544d8b9a30b63 100644
>> --- a/include/net/xdp.h
>> +++ b/include/net/xdp.h
>> @@ -586,6 +586,10 @@ void xdp_attachment_setup(struct xdp_attachment_info *info,
>>   			   NETDEV_XDP_RX_METADATA_VLAN_TAG, \
>>   			   bpf_xdp_metadata_rx_vlan_tag, \
>>   			   xmo_rx_vlan_tag) \
>> +	XDP_METADATA_KFUNC(XDP_METADATA_KFUNC_RX_CHECKSUM, \
>> +			   NETDEV_XDP_RX_METADATA_CHECKSUM, \
>> +			   bpf_xdp_metadata_rx_checksum, \
>> +			   xmo_rx_checksum)
>>   
>>   enum xdp_rx_metadata {
>>   #define XDP_METADATA_KFUNC(name, _, __, ___) name,
>> @@ -643,12 +647,22 @@ enum xdp_rss_hash_type {
>>   	XDP_RSS_TYPE_L4_IPV6_SCTP_EX = XDP_RSS_TYPE_L4_IPV6_SCTP | XDP_RSS_L3_DYNHDR,
>>   };
>>   
>> +enum xdp_checksum {
>> +	XDP_CHECKSUM_NONE		= CHECKSUM_NONE,
>> +	XDP_CHECKSUM_UNNECESSARY	= CHECKSUM_UNNECESSARY,
>> +	XDP_CHECKSUM_COMPLETE		= CHECKSUM_COMPLETE,
>> +	XDP_CHECKSUM_PARTIAL		= CHECKSUM_PARTIAL,
>> +};
> 
> Btw, might be worth mentioning, awhile ago we had settled on a smaller set of
> exposed types:
> 
> https://lore.kernel.org/netdev/20230811161509.19722-13-larysa.zaremba@intel.com/
> 
> Maybe go through the previous postings and check if the arguments are
> still relevant? (or explain why we want more checksum now)

IHMO the linked proposal reduced the types too much.

I think Lorenzo's suggested types are much better. One argument is of-
cause that the types corresponds directly to the (time proven) types
used by the SKB.

I could argue, that we are lacking a type that indicate hardware
"failed" to do the checksum, but that is indirectly covered by
CHECKSUM_NONE case.  And having BPF-developers deal with both
CHECKSUM_NONE and CHECKSUM_FAIL correctly is a recipe for bugs.

I will explain in another email, why we need to document what
CHECKSUM_NONE actually means.

--Jesper