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bpf: Add bpf_skc_to_tcp6_sock() helper

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The helper is used in tracing programs to cast a socket
pointer to a tcp6_sock pointer.
The return value could be NULL if the casting is illegal.

A new helper return type RET_PTR_TO_BTF_ID_OR_NULL is added
so the verifier is able to deduce proper return types for the helper.

Different from the previous BTF_ID based helpers,
the bpf_skc_to_tcp6_sock() argument can be several possible
btf_ids. More specifically, all possible socket data structures
with sock_common appearing in the first in the memory layout.
This patch only added socket types related to tcp and udp.

All possible argument btf_id and return value btf_id
for helper bpf_skc_to_tcp6_sock() are pre-calculcated and
cached. In the future, it is even possible to precompute
these btf_id's at kernel build time.

Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Acked-by: Andrii Nakryiko <andriin@fb.com>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Link: https://lore.kernel.org/bpf/20200623230809.3988195-1-yhs@fb.com
This commit is contained in:
Yonghong Song 2020-06-23 16:08:09 -07:00 • committed by Alexei Starovoitov
parent 72e2b2b66f
commit af7ec13833
8 changed files with 148 additions and 12 deletions
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9
tools/include/uapi/linux/bpf.h
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@ -3255,6 +3255,12 @@ union bpf_attr {
* 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.
*
* struct tcp6_sock *bpf_skc_to_tcp6_sock(void *sk)
* Description
* Dynamically cast a *sk* pointer to a *tcp6_sock* pointer.
* Return
* *sk* if casting is valid, or NULL otherwise.
*/
#define __BPF_FUNC_MAPPER(FN) \
FN(unspec), \
@ -3392,7 +3398,8 @@ union bpf_attr {
FN(ringbuf_submit), \
FN(ringbuf_discard), \
FN(ringbuf_query), \
FN(csum_level),
FN(csum_level), \
FN(skc_to_tcp6_sock),
/* integer value in 'imm' field of BPF_CALL instruction selects which helper
* function eBPF program intends to call