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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
parent a498cfe990
commit 9bac3d6d54
5 changed files with 234 additions and 35 deletions
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5
include/linux/bpf.h
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@@ -103,6 +103,9 @@ struct bpf_verifier_ops {
* with 'type' (read or write) is allowed
*/
bool (*is_valid_access)(int off, int size, enum bpf_access_type type);
u32 (*convert_ctx_access)(int dst_reg, int src_reg, int ctx_off,
struct bpf_insn *insn);
};
struct bpf_prog_type_list {
@@ -133,7 +136,7 @@ struct bpf_map *bpf_map_get(struct fd f);
void bpf_map_put(struct bpf_map *map);
/* verify correctness of eBPF program */
int bpf_check(struct bpf_prog *fp, union bpf_attr *attr);
int bpf_check(struct bpf_prog **fp, union bpf_attr *attr);
#else
static inline void bpf_register_prog_type(struct bpf_prog_type_list *tl)
{