bpf: add test case for ld_abs and helper changing pkt data

Add a test that i) uses LD_ABS, ii) zeroing R6 before call, iii) calls
a helper that triggers reload of cached skb data, iv) uses LD_ABS again.
It's added for test_bpf in order to do runtime testing after JITing as
well as test_verifier to test that the sequence is allowed.

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

lib/test_bpf.c

@@ -435,6 +435,41 @@ loop:
 	return 0;
 }
 
+static int bpf_fill_ld_abs_vlan_push_pop2(struct bpf_test *self)
+{
+	struct bpf_insn *insn;
+
+	insn = kmalloc_array(16, sizeof(*insn), GFP_KERNEL);
+	if (!insn)
+		return -ENOMEM;
+
+	/* Due to func address being non-const, we need to
+	 * assemble this here.
+	 */
+	insn[0] = BPF_MOV64_REG(R6, R1);
+	insn[1] = BPF_LD_ABS(BPF_B, 0);
+	insn[2] = BPF_LD_ABS(BPF_H, 0);
+	insn[3] = BPF_LD_ABS(BPF_W, 0);
+	insn[4] = BPF_MOV64_REG(R7, R6);
+	insn[5] = BPF_MOV64_IMM(R6, 0);
+	insn[6] = BPF_MOV64_REG(R1, R7);
+	insn[7] = BPF_MOV64_IMM(R2, 1);
+	insn[8] = BPF_MOV64_IMM(R3, 2);
+	insn[9] = BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0,
+			       bpf_skb_vlan_push_proto.func - __bpf_call_base);
+	insn[10] = BPF_MOV64_REG(R6, R7);
+	insn[11] = BPF_LD_ABS(BPF_B, 0);
+	insn[12] = BPF_LD_ABS(BPF_H, 0);
+	insn[13] = BPF_LD_ABS(BPF_W, 0);
+	insn[14] = BPF_MOV64_IMM(R0, 42);
+	insn[15] = BPF_EXIT_INSN();
+
+	self->u.ptr.insns = insn;
+	self->u.ptr.len = 16;
+
+	return 0;
+}
+
 static int bpf_fill_jump_around_ld_abs(struct bpf_test *self)
 {
 	unsigned int len = BPF_MAXINSNS;
@@ -6066,6 +6101,14 @@ static struct bpf_test tests[] = {
 		{},
 		{ {0x1, 0x42 } },
 	},
+	{
+		"LD_ABS with helper changing skb data",
+		{ },
+		INTERNAL,
+		{ 0x34 },
+		{ { ETH_HLEN, 42 } },
+		.fill_helper = bpf_fill_ld_abs_vlan_push_pop2,
+	},
 };
 
 static struct net_device dev;

tools/testing/selftests/bpf/test_verifier.c

@@ -6116,6 +6116,30 @@ static struct bpf_test tests[] = {
 		},
 		.result = ACCEPT,
 	},
+	{
+		"ld_abs: tests on r6 and skb data reload helper",
+		.insns = {
+			BPF_MOV64_REG(BPF_REG_6, BPF_REG_1),
+			BPF_LD_ABS(BPF_B, 0),
+			BPF_LD_ABS(BPF_H, 0),
+			BPF_LD_ABS(BPF_W, 0),
+			BPF_MOV64_REG(BPF_REG_7, BPF_REG_6),
+			BPF_MOV64_IMM(BPF_REG_6, 0),
+			BPF_MOV64_REG(BPF_REG_1, BPF_REG_7),
+			BPF_MOV64_IMM(BPF_REG_2, 1),
+			BPF_MOV64_IMM(BPF_REG_3, 2),
+			BPF_RAW_INSN(BPF_JMP | BPF_CALL, 0, 0, 0,
+				     BPF_FUNC_skb_vlan_push),
+			BPF_MOV64_REG(BPF_REG_6, BPF_REG_7),
+			BPF_LD_ABS(BPF_B, 0),
+			BPF_LD_ABS(BPF_H, 0),
+			BPF_LD_ABS(BPF_W, 0),
+			BPF_MOV64_IMM(BPF_REG_0, 42),
+			BPF_EXIT_INSN(),
+		},
+		.prog_type = BPF_PROG_TYPE_SCHED_CLS,
+		.result = ACCEPT,
+	},
 	{
 		"ld_ind: check calling conv, r1",
 		.insns = {