bpf/tests: Add JMP tests with small offsets

This patch adds a set of tests for JMP to verify that the JITed jump
offset is calculated correctly. We pretend that the verifier has inserted
any zero extensions to make the jump-over operations JIT to one
instruction each, in order to control the exact JITed jump offset.
Signed-off-by: Johan Almbladh <johan.almbladh@anyfinetworks.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20210914091842.4186267-10-johan.almbladh@anyfinetworks.com

lib/test_bpf.c

@@ -10709,6 +10709,77 @@ static struct bpf_test tests[] = {
 		.fill_helper = bpf_fill_jmp32_jsle_reg,
 		.nr_testruns = NR_PATTERN_RUNS,
 	},
+	/* Short relative jumps */
+	{
+		"Short relative jump: offset=0",
+		.u.insns_int = {
+			BPF_ALU64_IMM(BPF_MOV, R0, 0),
+			BPF_JMP_IMM(BPF_JEQ, R0, 0, 0),
+			BPF_EXIT_INSN(),
+			BPF_ALU32_IMM(BPF_MOV, R0, -1),
+		},
+		INTERNAL | FLAG_NO_DATA | FLAG_VERIFIER_ZEXT,
+		{ },
+		{ { 0, 0 } },
+	},
+	{
+		"Short relative jump: offset=1",
+		.u.insns_int = {
+			BPF_ALU64_IMM(BPF_MOV, R0, 0),
+			BPF_JMP_IMM(BPF_JEQ, R0, 0, 1),
+			BPF_ALU32_IMM(BPF_ADD, R0, 1),
+			BPF_EXIT_INSN(),
+			BPF_ALU32_IMM(BPF_MOV, R0, -1),
+		},
+		INTERNAL | FLAG_NO_DATA | FLAG_VERIFIER_ZEXT,
+		{ },
+		{ { 0, 0 } },
+	},
+	{
+		"Short relative jump: offset=2",
+		.u.insns_int = {
+			BPF_ALU64_IMM(BPF_MOV, R0, 0),
+			BPF_JMP_IMM(BPF_JEQ, R0, 0, 2),
+			BPF_ALU32_IMM(BPF_ADD, R0, 1),
+			BPF_ALU32_IMM(BPF_ADD, R0, 1),
+			BPF_EXIT_INSN(),
+			BPF_ALU32_IMM(BPF_MOV, R0, -1),
+		},
+		INTERNAL | FLAG_NO_DATA | FLAG_VERIFIER_ZEXT,
+		{ },
+		{ { 0, 0 } },
+	},
+	{
+		"Short relative jump: offset=3",
+		.u.insns_int = {
+			BPF_ALU64_IMM(BPF_MOV, R0, 0),
+			BPF_JMP_IMM(BPF_JEQ, R0, 0, 3),
+			BPF_ALU32_IMM(BPF_ADD, R0, 1),
+			BPF_ALU32_IMM(BPF_ADD, R0, 1),
+			BPF_ALU32_IMM(BPF_ADD, R0, 1),
+			BPF_EXIT_INSN(),
+			BPF_ALU32_IMM(BPF_MOV, R0, -1),
+		},
+		INTERNAL | FLAG_NO_DATA | FLAG_VERIFIER_ZEXT,
+		{ },
+		{ { 0, 0 } },
+	},
+	{
+		"Short relative jump: offset=4",
+		.u.insns_int = {
+			BPF_ALU64_IMM(BPF_MOV, R0, 0),
+			BPF_JMP_IMM(BPF_JEQ, R0, 0, 4),
+			BPF_ALU32_IMM(BPF_ADD, R0, 1),
+			BPF_ALU32_IMM(BPF_ADD, R0, 1),
+			BPF_ALU32_IMM(BPF_ADD, R0, 1),
+			BPF_ALU32_IMM(BPF_ADD, R0, 1),
+			BPF_EXIT_INSN(),
+			BPF_ALU32_IMM(BPF_MOV, R0, -1),
+		},
+		INTERNAL | FLAG_NO_DATA | FLAG_VERIFIER_ZEXT,
+		{ },
+		{ { 0, 0 } },
+	},
 	/* Staggered jump sequences, immediate */
 	{
 		"Staggered jumps: JMP_JA",