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bpf: allow BPF programs access 'protocol' and 'vlan_tci' fields
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as a follow on to patch 70006af ("bpf: allow eBPF access skb fields")
this patch allows 'protocol' and 'vlan_tci' fields to be accessible
from extended BPF programs.

The usage of 'protocol', 'vlan_present' and 'vlan_tci' fields is the same as
corresponding SKF_AD_PROTOCOL, SKF_AD_VLAN_TAG_PRESENT and SKF_AD_VLAN_TAG
accesses in classic BPF.

Signed-off-by: Alexei Starovoitov <[email protected]>
Signed-off-by: David S. Miller <[email protected]>
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@davem330
Alexei Starovoitov authored and davem330 committed Mar 17, 2015
1 parent 9cf7867 commit c249739
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Showing 3 changed files with 62 additions and 22 deletions.
3 changes: 3 additions & 0 deletions include/uapi/linux/bpf.h
View file
Original file line number Diff line number Diff line change
Expand Up @@ -178,6 +178,9 @@ struct __sk_buff {
__u32 pkt_type;
__u32 mark;
__u32 queue_mapping;
__u32 protocol;
__u32 vlan_present;
__u32 vlan_tci;
};

#endif /* _UAPI__LINUX_BPF_H__ */
72 changes: 50 additions & 22 deletions net/core/filter.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -177,6 +177,35 @@ static u32 convert_skb_access(int skb_field, int dst_reg, int src_reg,
*insn++ = BPF_LDX_MEM(BPF_H, dst_reg, src_reg,
offsetof(struct sk_buff, queue_mapping));
break;

case SKF_AD_PROTOCOL:
BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, protocol) != 2);

/* dst_reg = *(u16 *) (src_reg + offsetof(protocol)) */
*insn++ = BPF_LDX_MEM(BPF_H, dst_reg, src_reg,
offsetof(struct sk_buff, protocol));
/* dst_reg = ntohs(dst_reg) [emitting a nop or swap16] */
*insn++ = BPF_ENDIAN(BPF_FROM_BE, dst_reg, 16);
break;

case SKF_AD_VLAN_TAG:
case SKF_AD_VLAN_TAG_PRESENT:
BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, vlan_tci) != 2);
BUILD_BUG_ON(VLAN_TAG_PRESENT != 0x1000);

/* dst_reg = *(u16 *) (src_reg + offsetof(vlan_tci)) */
*insn++ = BPF_LDX_MEM(BPF_H, dst_reg, src_reg,
offsetof(struct sk_buff, vlan_tci));
if (skb_field == SKF_AD_VLAN_TAG) {
*insn++ = BPF_ALU32_IMM(BPF_AND, dst_reg,
~VLAN_TAG_PRESENT);
} else {
/* dst_reg >>= 12 */
*insn++ = BPF_ALU32_IMM(BPF_RSH, dst_reg, 12);
/* dst_reg &= 1 */
*insn++ = BPF_ALU32_IMM(BPF_AND, dst_reg, 1);
}
break;
}

return insn - insn_buf;
Expand All @@ -190,13 +219,8 @@ static bool convert_bpf_extensions(struct sock_filter *fp,

switch (fp->k) {
case SKF_AD_OFF + SKF_AD_PROTOCOL:
BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, protocol) != 2);

/* A = *(u16 *) (CTX + offsetof(protocol)) */
*insn++ = BPF_LDX_MEM(BPF_H, BPF_REG_A, BPF_REG_CTX,
offsetof(struct sk_buff, protocol));
/* A = ntohs(A) [emitting a nop or swap16] */
*insn = BPF_ENDIAN(BPF_FROM_BE, BPF_REG_A, 16);
cnt = convert_skb_access(SKF_AD_PROTOCOL, BPF_REG_A, BPF_REG_CTX, insn);
insn += cnt - 1;
break;

case SKF_AD_OFF + SKF_AD_PKTTYPE:
Expand Down Expand Up @@ -242,22 +266,15 @@ static bool convert_bpf_extensions(struct sock_filter *fp,
break;

case SKF_AD_OFF + SKF_AD_VLAN_TAG:
case SKF_AD_OFF + SKF_AD_VLAN_TAG_PRESENT:
BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, vlan_tci) != 2);
BUILD_BUG_ON(VLAN_TAG_PRESENT != 0x1000);
cnt = convert_skb_access(SKF_AD_VLAN_TAG,
BPF_REG_A, BPF_REG_CTX, insn);
insn += cnt - 1;
break;

/* A = *(u16 *) (CTX + offsetof(vlan_tci)) */
*insn++ = BPF_LDX_MEM(BPF_H, BPF_REG_A, BPF_REG_CTX,
offsetof(struct sk_buff, vlan_tci));
if (fp->k == SKF_AD_OFF + SKF_AD_VLAN_TAG) {
*insn = BPF_ALU32_IMM(BPF_AND, BPF_REG_A,
~VLAN_TAG_PRESENT);
} else {
/* A >>= 12 */
*insn++ = BPF_ALU32_IMM(BPF_RSH, BPF_REG_A, 12);
/* A &= 1 */
*insn = BPF_ALU32_IMM(BPF_AND, BPF_REG_A, 1);
}
case SKF_AD_OFF + SKF_AD_VLAN_TAG_PRESENT:
cnt = convert_skb_access(SKF_AD_VLAN_TAG_PRESENT,
BPF_REG_A, BPF_REG_CTX, insn);
insn += cnt - 1;
break;

case SKF_AD_OFF + SKF_AD_PAY_OFFSET:
Expand Down Expand Up @@ -1215,6 +1232,17 @@ static u32 sk_filter_convert_ctx_access(int dst_reg, int src_reg, int ctx_off,

case offsetof(struct __sk_buff, queue_mapping):
return convert_skb_access(SKF_AD_QUEUE, dst_reg, src_reg, insn);

case offsetof(struct __sk_buff, protocol):
return convert_skb_access(SKF_AD_PROTOCOL, dst_reg, src_reg, insn);

case offsetof(struct __sk_buff, vlan_present):
return convert_skb_access(SKF_AD_VLAN_TAG_PRESENT,
dst_reg, src_reg, insn);

case offsetof(struct __sk_buff, vlan_tci):
return convert_skb_access(SKF_AD_VLAN_TAG,
dst_reg, src_reg, insn);
}

return insn - insn_buf;
Expand Down
9 changes: 9 additions & 0 deletions samples/bpf/test_verifier.c
View file
Original file line number Diff line number Diff line change
Expand Up @@ -658,6 +658,15 @@ static struct bpf_test tests[] = {
BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_1,
offsetof(struct __sk_buff, queue_mapping)),
BPF_JMP_IMM(BPF_JGE, BPF_REG_0, 0, 0),
BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_1,
offsetof(struct __sk_buff, protocol)),
BPF_JMP_IMM(BPF_JGE, BPF_REG_0, 0, 0),
BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_1,
offsetof(struct __sk_buff, vlan_present)),
BPF_JMP_IMM(BPF_JGE, BPF_REG_0, 0, 0),
BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_1,
offsetof(struct __sk_buff, vlan_tci)),
BPF_JMP_IMM(BPF_JGE, BPF_REG_0, 0, 0),
BPF_EXIT_INSN(),
},
.result = ACCEPT,
Expand Down

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