diff options
| author | Daniel Borkmann <daniel@iogearbox.net> | 2015-03-19 19:38:27 +0100 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2015-03-20 15:24:26 -0400 |
| commit | 0b8c707ddf37171413fe67350263e5b6ffeedf7c (patch) | |
| tree | e2f6a1849cc78ec2cc41846718ad3076e84de0cd | |
| parent | c4a6853d8fb2b122686bc6a7c472956e87090f4e (diff) | |
ebpf, filter: do not convert skb->protocol to host endianess during runtime
Commit c24973957975 ("bpf: allow BPF programs access 'protocol' and 'vlan_tci'
fields") has added support for accessing protocol, vlan_present and vlan_tci
into the skb offset map.
As referenced in the below discussion, accessing skb->protocol from an eBPF
program should be converted without handling endianess.
The reason for this is that an eBPF program could simply do a check more
naturally, by f.e. testing skb->protocol == htons(ETH_P_IP), where the LLVM
compiler resolves htons() against a constant automatically during compilation
time, as opposed to an otherwise needed run time conversion.
After all, the way of programming both from a user perspective differs quite
a lot, i.e. bpf_asm ["ld proto"] versus a C subset/LLVM.
Reference: https://patchwork.ozlabs.org/patch/450819/
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@plumgrid.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
| -rw-r--r-- | net/core/filter.c | 29 |
1 files changed, 14 insertions, 15 deletions
diff --git a/net/core/filter.c b/net/core/filter.c index b95ae7fe7e4f..bdaac5895def 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -178,16 +178,6 @@ static u32 convert_skb_access(int skb_field, int dst_reg, int 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); @@ -219,8 +209,13 @@ static bool convert_bpf_extensions(struct sock_filter *fp, switch (fp->k) { case SKF_AD_OFF + SKF_AD_PROTOCOL: - cnt = convert_skb_access(SKF_AD_PROTOCOL, BPF_REG_A, BPF_REG_CTX, insn); - insn += cnt - 1; + 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); break; case SKF_AD_OFF + SKF_AD_PKTTYPE: @@ -1224,6 +1219,13 @@ static u32 sk_filter_convert_ctx_access(int dst_reg, int src_reg, int ctx_off, offsetof(struct sk_buff, len)); break; + case offsetof(struct __sk_buff, protocol): + BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, protocol) != 2); + + *insn++ = BPF_LDX_MEM(BPF_H, dst_reg, src_reg, + offsetof(struct sk_buff, protocol)); + break; + case offsetof(struct __sk_buff, mark): return convert_skb_access(SKF_AD_MARK, dst_reg, src_reg, insn); @@ -1233,9 +1235,6 @@ 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); |