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bpf: allow extended BPF programs access skb fields

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introduce user accessible mirror of in-kernel 'struct sk_buff':
struct __sk_buff {
    __u32 len;
    __u32 pkt_type;
    __u32 mark;
    __u32 queue_mapping;
};

bpf programs can do:

int bpf_prog(struct __sk_buff *skb)
{
    __u32 var = skb->pkt_type;

which will be compiled to bpf assembler as:

dst_reg = *(u32 *)(src_reg + 4) // 4 == offsetof(struct __sk_buff, pkt_type)

bpf verifier will check validity of access and will convert it to:

dst_reg = *(u8 *)(src_reg + offsetof(struct sk_buff, __pkt_type_offset))
dst_reg &= 7

since skb->pkt_type is a bitfield.

Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Alexei Starovoitov 2015-03-13 11:57:42 -07:00 • committed by David S. Miller
commit 9bac3d6d54
5 changed files with 234 additions and 35 deletions
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10
include/uapi/linux/bpf.h
View file

@ -170,4 +170,14 @@ enum bpf_func_id {
__BPF_FUNC_MAX_ID,
};
/* user accessible mirror of in-kernel sk_buff.
* new fields can only be added to the end of this structure
*/
struct __sk_buff {
__u32 len;
__u32 pkt_type;
__u32 mark;
__u32 queue_mapping;
};
#endif /* _UAPI__LINUX_BPF_H__ */