KFunc bpf_rdonly_cast

v6.2

Definition

This kfunc tries to cast the object to a specified type.

The function returns the same obj but with PTR_TO_BTF_ID with btf_id. The verifier will ensure btf_id being a struct type.

Since the supported type cast may not reflect what the 'obj' represents, the returned btf_id is marked as PTR_UNTRUSTED, so the return value and subsequent pointer chasing cannot be used as helper/kfunc arguments.

void *bpf_rdonly_cast(void *obj__ign, u32 btf_id__k)

Usage

This tries to support use case like below:

#define skb_shinfo(SKB) ((struct skb_shared_info *)(skb_end_pointer(SKB)))

where skb_end_pointer(SKB) is a unsigned char * and needs to be casted to struct skb_shared_info *.

Program types

The following program types can make use of this kfunc:

• BPF_PROG_TYPE_CGROUP_SKB
• BPF_PROG_TYPE_CGROUP_SOCK_ADDR
• BPF_PROG_TYPE_LSM
• BPF_PROG_TYPE_LWT_IN
• BPF_PROG_TYPE_LWT_OUT
• BPF_PROG_TYPE_LWT_SEG6LOCAL
• BPF_PROG_TYPE_LWT_XMIT
• BPF_PROG_TYPE_NETFILTER
• BPF_PROG_TYPE_SCHED_ACT
• BPF_PROG_TYPE_SCHED_CLS
• BPF_PROG_TYPE_SK_SKB
• BPF_PROG_TYPE_SOCKET_FILTER
• BPF_PROG_TYPE_STRUCT_OPS
• BPF_PROG_TYPE_SYSCALL
• BPF_PROG_TYPE_TRACING
• BPF_PROG_TYPE_XDP

Example

Docs could be improved

This part of the docs is incomplete, contributions are very welcome