On 03/13/2015 07:57 PM, Alexei Starovoitov wrote:
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 <a...@plumgrid.com>
...
+static u32 convert_skb_access(int skb_field, int dst_reg, int src_reg,
+ struct bpf_insn *insn_buf)
+{
+ struct bpf_insn *insn = insn_buf;
+
+ switch (skb_field) {
+ case SKF_AD_MARK:
+ BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, mark) != 4);
+
+ *insn++ = BPF_LDX_MEM(BPF_W, dst_reg, src_reg,
+ offsetof(struct sk_buff, mark));
+ break;
+
+ case SKF_AD_PKTTYPE:
+ *insn++ = BPF_LDX_MEM(BPF_B, dst_reg, src_reg,
PKT_TYPE_OFFSET());
+ *insn++ = BPF_ALU32_IMM(BPF_AND, dst_reg, PKT_TYPE_MAX);
+#ifdef __BIG_ENDIAN_BITFIELD
+ *insn++ = BPF_ALU32_IMM(BPF_RSH, dst_reg, 5);
+#endif
+ break;
+
+ case SKF_AD_QUEUE:
+ BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, queue_mapping) != 2);
+
+ *insn++ = BPF_LDX_MEM(BPF_H, dst_reg, src_reg,
+ offsetof(struct sk_buff, queue_mapping));
+ break;
+ }
+
+ return insn - insn_buf;
+}
+
static bool convert_bpf_extensions(struct sock_filter *fp,
struct bpf_insn **insnp)
{
struct bpf_insn *insn = *insnp;
+ u32 cnt;
switch (fp->k) {
case SKF_AD_OFF + SKF_AD_PROTOCOL:
@@ -167,13 +200,8 @@ static bool convert_bpf_extensions(struct sock_filter *fp,
break;
case SKF_AD_OFF + SKF_AD_PKTTYPE:
- *insn++ = BPF_LDX_MEM(BPF_B, BPF_REG_A, BPF_REG_CTX,
- PKT_TYPE_OFFSET());
- *insn = BPF_ALU32_IMM(BPF_AND, BPF_REG_A, PKT_TYPE_MAX);
-#ifdef __BIG_ENDIAN_BITFIELD
- insn++;
- *insn = BPF_ALU32_IMM(BPF_RSH, BPF_REG_A, 5);
-#endif
+ cnt = convert_skb_access(SKF_AD_PKTTYPE, BPF_REG_A,
BPF_REG_CTX, insn);
+ insn += cnt - 1;
break;
case SKF_AD_OFF + SKF_AD_IFINDEX:
@@ -197,10 +225,8 @@ static bool convert_bpf_extensions(struct sock_filter *fp,
break;
case SKF_AD_OFF + SKF_AD_MARK:
- BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, mark) != 4);
-
- *insn = BPF_LDX_MEM(BPF_W, BPF_REG_A, BPF_REG_CTX,
- offsetof(struct sk_buff, mark));
+ cnt = convert_skb_access(SKF_AD_MARK, BPF_REG_A, BPF_REG_CTX,
insn);
+ insn += cnt - 1;
break;
case SKF_AD_OFF + SKF_AD_RXHASH:
@@ -211,10 +237,8 @@ static bool convert_bpf_extensions(struct sock_filter *fp,
break;
case SKF_AD_OFF + SKF_AD_QUEUE:
- BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, queue_mapping) != 2);
-
- *insn = BPF_LDX_MEM(BPF_H, BPF_REG_A, BPF_REG_CTX,
- offsetof(struct sk_buff, queue_mapping));
+ cnt = convert_skb_access(SKF_AD_QUEUE, BPF_REG_A, BPF_REG_CTX,
insn);
+ insn += cnt - 1;
break;
case SKF_AD_OFF + SKF_AD_VLAN_TAG:
@@ -1147,13 +1171,55 @@ sk_filter_func_proto(enum bpf_func_id func_id)
...
+static u32 sk_filter_convert_ctx_access(int dst_reg, int src_reg, int ctx_off,
+ struct bpf_insn *insn_buf)
+{
+ struct bpf_insn *insn = insn_buf;
+
+ switch (ctx_off) {
+ case offsetof(struct __sk_buff, len):
+ BUILD_BUG_ON(FIELD_SIZEOF(struct sk_buff, len) != 4);
+
+ *insn++ = BPF_LDX_MEM(BPF_W, dst_reg, src_reg,
+ offsetof(struct sk_buff, len));
+ break;
+
+ case offsetof(struct __sk_buff, mark):
+ return convert_skb_access(SKF_AD_MARK, dst_reg, src_reg, insn);
+
+ case offsetof(struct __sk_buff, pkt_type):
+ return convert_skb_access(SKF_AD_PKTTYPE, dst_reg, src_reg,
insn);
+
+ case offsetof(struct __sk_buff, queue_mapping):
+ return convert_skb_access(SKF_AD_QUEUE, dst_reg, src_reg, insn);
+ }
+
+ return insn - insn_buf;
}
Hmm, I actually liked the previous version much better. :(
Now, some members use convert_skb_access() and some skb members are
converted directly in-place in both, convert_bpf_extensions() _and_
in sk_filter_convert_ctx_access().
Previously, it was much more consistent, which I like better. And only
because of the simple BUILD_BUG_ON()? :/
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