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bpf: Add csum_level helper for fixing up csum levels

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Add a bpf_csum_level() helper which BPF programs can use in combination
with bpf_skb_adjust_room() when they pass in BPF_F_ADJ_ROOM_NO_CSUM_RESET
flag to the latter to avoid falling back to CHECKSUM_NONE.

The bpf_csum_level() allows to adjust CHECKSUM_UNNECESSARY skb->csum_levels
via BPF_CSUM_LEVEL_{INC,DEC} which calls __skb_{incr,decr}_checksum_unnecessary()
on the skb. The helper also allows a BPF_CSUM_LEVEL_RESET which sets the skb's
csum to CHECKSUM_NONE as well as a BPF_CSUM_LEVEL_QUERY to just return the
current level. Without this helper, there is no way to otherwise adjust the
skb->csum_level. I did not add an extra dummy flags as there is plenty of free
bitspace in level argument itself iff ever needed in future.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Reviewed-by: Alan Maguire <alan.maguire@oracle.com>
Acked-by: Lorenz Bauer <lmb@cloudflare.com>
Link: https://lore.kernel.org/bpf/279ae3717cb3d03c0ffeb511493c93c450a01e1a.1591108731.git.daniel@iogearbox.net
This commit is contained in:
Daniel Borkmann 2020-06-02 16:58:33 +02:00 committed by Andrii Nakryiko
parent 3aadd91e97
commit adb5dd203c
1 changed files with 42 additions and 1 deletions
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43
include/uapi/linux/bpf.h
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@ -3220,6 +3220,38 @@ union bpf_attr {
* calculation.
* Return
* Requested value, or 0, if flags are not recognized.
*
* int bpf_csum_level(struct sk_buff *skb, u64 level)
* Description
* Change the skbs checksum level by one layer up or down, or
* reset it entirely to none in order to have the stack perform
* checksum validation. The level is applicable to the following
* protocols: TCP, UDP, GRE, SCTP, FCOE. For example, a decap of
* | ETH | IP | UDP | GUE | IP | TCP | into | ETH | IP | TCP |
* through **bpf_skb_adjust_room**\ () helper with passing in
* **BPF_F_ADJ_ROOM_NO_CSUM_RESET** flag would require one call
* to **bpf_csum_level**\ () with **BPF_CSUM_LEVEL_DEC** since
* the UDP header is removed. Similarly, an encap of the latter
* into the former could be accompanied by a helper call to
* **bpf_csum_level**\ () with **BPF_CSUM_LEVEL_INC** if the
* skb is still intended to be processed in higher layers of the
* stack instead of just egressing at tc.
*
* There are three supported level settings at this time:
*
* * **BPF_CSUM_LEVEL_INC**: Increases skb->csum_level for skbs
* with CHECKSUM_UNNECESSARY.
* * **BPF_CSUM_LEVEL_DEC**: Decreases skb->csum_level for skbs
* with CHECKSUM_UNNECESSARY.
* * **BPF_CSUM_LEVEL_RESET**: Resets skb->csum_level to 0 and
* sets CHECKSUM_NONE to force checksum validation by the stack.
* * **BPF_CSUM_LEVEL_QUERY**: No-op, returns the current
* skb->csum_level.
* Return
* 0 on success, or a negative error in case of failure. In the
* case of **BPF_CSUM_LEVEL_QUERY**, the current skb->csum_level
* is returned or the error code -EACCES in case the skb is not
* subject to CHECKSUM_UNNECESSARY.
*/
#define __BPF_FUNC_MAPPER(FN) \
FN(unspec), \
@ -3356,7 +3388,8 @@ union bpf_attr {
FN(ringbuf_reserve), \
FN(ringbuf_submit), \
FN(ringbuf_discard), \
FN(ringbuf_query),
FN(ringbuf_query), \
FN(csum_level),
/* integer value in 'imm' field of BPF_CALL instruction selects which helper
* function eBPF program intends to call
@ -3433,6 +3466,14 @@ enum {
BPF_F_CURRENT_NETNS = (-1L),
};
/* BPF_FUNC_csum_level level values. */
enum {
BPF_CSUM_LEVEL_QUERY,
BPF_CSUM_LEVEL_INC,
BPF_CSUM_LEVEL_DEC,
BPF_CSUM_LEVEL_RESET,
};
/* BPF_FUNC_skb_adjust_room flags. */
enum {
BPF_F_ADJ_ROOM_FIXED_GSO = (1ULL << 0),