selftests/bpf: Add asm tests for pkt vs pkt_end comparison.

Add few assembly tests for packet comparison.
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Tested-by: Jiri Olsa <jolsa@redhat.com>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20201111031213.25109-4-alexei.starovoitov@gmail.com

tools/testing/selftests/bpf/verifier/ctx_skb.c

@@ -1089,3 +1089,45 @@
 	.errstr_unpriv = "R1 leaks addr",
 	.result = REJECT,
 },
+{
+       "pkt > pkt_end taken check",
+       .insns = {
+       BPF_LDX_MEM(BPF_W, BPF_REG_2, BPF_REG_1,                //  0. r2 = *(u32 *)(r1 + data_end)
+                   offsetof(struct __sk_buff, data_end)),
+       BPF_LDX_MEM(BPF_W, BPF_REG_4, BPF_REG_1,                //  1. r4 = *(u32 *)(r1 + data)
+                   offsetof(struct __sk_buff, data)),
+       BPF_MOV64_REG(BPF_REG_3, BPF_REG_4),                    //  2. r3 = r4
+       BPF_ALU64_IMM(BPF_ADD, BPF_REG_3, 42),                  //  3. r3 += 42
+       BPF_MOV64_IMM(BPF_REG_1, 0),                            //  4. r1 = 0
+       BPF_JMP_REG(BPF_JGT, BPF_REG_3, BPF_REG_2, 2),          //  5. if r3 > r2 goto 8
+       BPF_ALU64_IMM(BPF_ADD, BPF_REG_4, 14),                  //  6. r4 += 14
+       BPF_MOV64_REG(BPF_REG_1, BPF_REG_4),                    //  7. r1 = r4
+       BPF_JMP_REG(BPF_JGT, BPF_REG_3, BPF_REG_2, 1),          //  8. if r3 > r2 goto 10
+       BPF_LDX_MEM(BPF_H, BPF_REG_2, BPF_REG_1, 9),            //  9. r2 = *(u8 *)(r1 + 9)
+       BPF_MOV64_IMM(BPF_REG_0, 0),                            // 10. r0 = 0
+       BPF_EXIT_INSN(),                                        // 11. exit
+       },
+       .result = ACCEPT,
+       .prog_type = BPF_PROG_TYPE_SK_SKB,
+},
+{
+       "pkt_end < pkt taken check",
+       .insns = {
+       BPF_LDX_MEM(BPF_W, BPF_REG_2, BPF_REG_1,                //  0. r2 = *(u32 *)(r1 + data_end)
+                   offsetof(struct __sk_buff, data_end)),
+       BPF_LDX_MEM(BPF_W, BPF_REG_4, BPF_REG_1,                //  1. r4 = *(u32 *)(r1 + data)
+                   offsetof(struct __sk_buff, data)),
+       BPF_MOV64_REG(BPF_REG_3, BPF_REG_4),                    //  2. r3 = r4
+       BPF_ALU64_IMM(BPF_ADD, BPF_REG_3, 42),                  //  3. r3 += 42
+       BPF_MOV64_IMM(BPF_REG_1, 0),                            //  4. r1 = 0
+       BPF_JMP_REG(BPF_JGT, BPF_REG_3, BPF_REG_2, 2),          //  5. if r3 > r2 goto 8
+       BPF_ALU64_IMM(BPF_ADD, BPF_REG_4, 14),                  //  6. r4 += 14
+       BPF_MOV64_REG(BPF_REG_1, BPF_REG_4),                    //  7. r1 = r4
+       BPF_JMP_REG(BPF_JLT, BPF_REG_2, BPF_REG_3, 1),          //  8. if r2 < r3 goto 10
+       BPF_LDX_MEM(BPF_H, BPF_REG_2, BPF_REG_1, 9),            //  9. r2 = *(u8 *)(r1 + 9)
+       BPF_MOV64_IMM(BPF_REG_0, 0),                            // 10. r0 = 0
+       BPF_EXIT_INSN(),                                        // 11. exit
+       },
+       .result = ACCEPT,
+       .prog_type = BPF_PROG_TYPE_SK_SKB,
+},