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Commit d9ff286a authored by Eric Dumazet's avatar Eric Dumazet Committed by Daniel Borkmann
Browse files

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: default avatarEric Dumazet <edumazet@google.com>
Cc: Eddie Hao <eddieh@google.com>
Cc: Martin KaFai Lau <kafai@fb.com>
Acked-by: default avatarMartin KaFai Lau <kafai@fb.com>
Signed-off-by: default avatarDaniel Borkmann <daniel@iogearbox.net>
parent 866e6ac4

include/uapi/linux/bpf.h

+1 −0
Original line number Diff line number Diff line
@@ -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 {

net/core/filter.c

+21 −0
Original line number Diff line number Diff line
@@ -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);

tools/include/uapi/linux/bpf.h

+1 −0
Original line number Diff line number Diff line
@@ -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 {

tools/testing/selftests/bpf/test_verifier.c

+36 −0
Original line number Diff line number Diff line
@@ -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 = {