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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 Alexei Starovoitov
parent 836e66c218
commit 7cdec54f97
3 changed files with 122 additions and 2 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

43
include/uapi/linux/bpf.h
View File

@ -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),

38
net/core/filter.c
View File

@ -2015,6 +2015,40 @@ static const struct bpf_func_proto bpf_csum_update_proto = {
.arg2_type = ARG_ANYTHING,
};
BPF_CALL_2(bpf_csum_level, struct sk_buff *, skb, u64, level)
{
/* The interface is to be used in combination with bpf_skb_adjust_room()
* for encap/decap of packet headers when BPF_F_ADJ_ROOM_NO_CSUM_RESET
* is passed as flags, for example.
*/
switch (level) {
case BPF_CSUM_LEVEL_INC:
__skb_incr_checksum_unnecessary(skb);
break;
case BPF_CSUM_LEVEL_DEC:
__skb_decr_checksum_unnecessary(skb);
break;
case BPF_CSUM_LEVEL_RESET:
__skb_reset_checksum_unnecessary(skb);
break;
case BPF_CSUM_LEVEL_QUERY:
return skb->ip_summed == CHECKSUM_UNNECESSARY ?
skb->csum_level : -EACCES;
default:
return -EINVAL;
}
return 0;
}
static const struct bpf_func_proto bpf_csum_level_proto = {
.func = bpf_csum_level,
.gpl_only = false,
.ret_type = RET_INTEGER,
.arg1_type = ARG_PTR_TO_CTX,
.arg2_type = ARG_ANYTHING,
};
static inline int __bpf_rx_skb(struct net_device *dev, struct sk_buff *skb)
{
return dev_forward_skb(dev, skb);
@ -6280,6 +6314,8 @@ tc_cls_act_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
return &bpf_csum_diff_proto;
case BPF_FUNC_csum_update:
return &bpf_csum_update_proto;
case BPF_FUNC_csum_level:
return &bpf_csum_level_proto;
case BPF_FUNC_l3_csum_replace:
return &bpf_l3_csum_replace_proto;
case BPF_FUNC_l4_csum_replace:
@ -6613,6 +6649,8 @@ lwt_xmit_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
return &bpf_skb_store_bytes_proto;
case BPF_FUNC_csum_update:
return &bpf_csum_update_proto;
case BPF_FUNC_csum_level:
return &bpf_csum_level_proto;
case BPF_FUNC_l3_csum_replace:
return &bpf_l3_csum_replace_proto;
case BPF_FUNC_l4_csum_replace:

43
tools/include/uapi/linux/bpf.h
View File

@ -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),