bpf: allow BPF programs access skb_shared_info->gso_segs field

This adds the ability to read gso_segs from a BPF program.

v3: Use BPF_REG_AX instead of BPF_REG_TMP for the temporary register,
    as suggested by Martin.

v2: refined Eddie Hao patch to address Alexei feedback.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Eddie Hao <eddieh@google.com>
Cc: Martin KaFai Lau <kafai@fb.com>
Acked-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

diff --git a/include/uapi/linux/bpf.h b/include/uapi/linux/bpf.h
index 91c4388..2940a98 100644 (file)
--- a/include/uapi/linux/bpf.h
+++ b/include/uapi/linux/bpf.h
@@ -2540,6 +2540,7 @@ struct __sk_buff {
        __bpf_md_ptr(struct bpf_flow_keys *, flow_keys);
        __u64 tstamp;
        __u32 wire_len;
+       __u32 gso_segs;
 };
 
 struct bpf_tunnel_key {

diff --git a/net/core/filter.c b/net/core/filter.c
index 2b3b436..8e587dd 100644 (file)
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -6700,6 +6700,27 @@ static u32 bpf_convert_ctx_access(enum bpf_access_type type,
                                                             target_size));
                break;
 
+       case offsetof(struct __sk_buff, gso_segs):
+               /* si->dst_reg = skb_shinfo(SKB); */
+#ifdef NET_SKBUFF_DATA_USES_OFFSET
+               *insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(struct sk_buff, head),
+                                     si->dst_reg, si->src_reg,
+                                     offsetof(struct sk_buff, head));
+               *insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(struct sk_buff, end),
+                                     BPF_REG_AX, si->src_reg,
+                                     offsetof(struct sk_buff, end));
+               *insn++ = BPF_ALU64_REG(BPF_ADD, si->dst_reg, BPF_REG_AX);
+#else
+               *insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(struct sk_buff, end),
+                                     si->dst_reg, si->src_reg,
+                                     offsetof(struct sk_buff, end));
+#endif
+               *insn++ = BPF_LDX_MEM(BPF_FIELD_SIZEOF(struct skb_shared_info, gso_segs),
+                                     si->dst_reg, si->dst_reg,
+                                     bpf_target_off(struct skb_shared_info,
+                                                    gso_segs, 2,
+                                                    target_size));
+               break;
        case offsetof(struct __sk_buff, wire_len):
                BUILD_BUG_ON(FIELD_SIZEOF(struct qdisc_skb_cb, pkt_len) != 4);
 

diff --git a/tools/include/uapi/linux/bpf.h b/tools/include/uapi/linux/bpf.h
index 91c4388..2940a98 100644 (file)
--- a/tools/include/uapi/linux/bpf.h
+++ b/tools/include/uapi/linux/bpf.h
@@ -2540,6 +2540,7 @@ struct __sk_buff {
        __bpf_md_ptr(struct bpf_flow_keys *, flow_keys);
        __u64 tstamp;
        __u32 wire_len;
+       __u32 gso_segs;
 };
 
 struct bpf_tunnel_key {

diff --git a/tools/testing/selftests/bpf/test_verifier.c b/tools/testing/selftests/bpf/test_verifier.c
index 4f67afe..e4fef6c 100644 (file)
--- a/tools/testing/selftests/bpf/test_verifier.c
+++ b/tools/testing/selftests/bpf/test_verifier.c
@@ -5663,6 +5663,42 @@ static struct bpf_test tests[] = {
                .result = ACCEPT,
                .prog_type = BPF_PROG_TYPE_CGROUP_SKB,
        },
+       {
+               "read gso_segs from CGROUP_SKB",
+               .insns = {
+                       BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_1,
+                                   offsetof(struct __sk_buff, gso_segs)),
+                       BPF_MOV64_IMM(BPF_REG_0, 0),
+                       BPF_EXIT_INSN(),
+               },
+               .result = ACCEPT,
+               .prog_type = BPF_PROG_TYPE_CGROUP_SKB,
+       },
+       {
+               "write gso_segs from CGROUP_SKB",
+               .insns = {
+                       BPF_MOV64_IMM(BPF_REG_0, 0),
+                       BPF_STX_MEM(BPF_W, BPF_REG_1, BPF_REG_0,
+                                   offsetof(struct __sk_buff, gso_segs)),
+                       BPF_MOV64_IMM(BPF_REG_0, 0),
+                       BPF_EXIT_INSN(),
+               },
+               .result = REJECT,
+               .result_unpriv = REJECT,
+               .errstr = "invalid bpf_context access off=164 size=4",
+               .prog_type = BPF_PROG_TYPE_CGROUP_SKB,
+       },
+       {
+               "read gso_segs from CLS",
+               .insns = {
+                       BPF_LDX_MEM(BPF_W, BPF_REG_0, BPF_REG_1,
+                                   offsetof(struct __sk_buff, gso_segs)),
+                       BPF_MOV64_IMM(BPF_REG_0, 0),
+                       BPF_EXIT_INSN(),
+               },
+               .result = ACCEPT,
+               .prog_type = BPF_PROG_TYPE_SCHED_CLS,
+       },
        {
                "multiple registers share map_lookup_elem result",
                .insns = {