bpf, selftests: Add verifier test case for jmp32's jeq/jne

Add a test case to trigger the verifier's incorrect conclusion in the
case of jmp32's jeq/jne. Also here, make use of dead code elimination,
so that we can see the verifier bailing out on unfixed kernels.

Before:

  # ./test_verifier 724
  #724/p jeq32/jne32: bounds checking FAIL
  Failed to load prog 'Permission denied'!
  R4 !read_ok
  verification time 8 usec
  stack depth 0
  processed 8 insns (limit 1000000) max_states_per_insn 0 total_states 1 peak_states 1 mark_read 0
  Summary: 0 PASSED, 0 SKIPPED, 1 FAILED

After:

  # ./test_verifier 724
  #724/p jeq32/jne32: bounds checking OK
  Summary: 1 PASSED, 0 SKIPPED, 0 FAILED

Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20220701124727.11153-4-daniel@iogearbox.net

tools/testing/selftests/bpf/verifier/jmp32.c

@@ -864,3 +864,24 @@
 	.result = ACCEPT,
 	.flags = F_NEEDS_EFFICIENT_UNALIGNED_ACCESS,
 },
+{
+	"jeq32/jne32: bounds checking",
+	.insns = {
+	BPF_MOV64_IMM(BPF_REG_6, 563),
+	BPF_MOV64_IMM(BPF_REG_2, 0),
+	BPF_ALU64_IMM(BPF_NEG, BPF_REG_2, 0),
+	BPF_ALU64_IMM(BPF_NEG, BPF_REG_2, 0),
+	BPF_ALU32_REG(BPF_OR, BPF_REG_2, BPF_REG_6),
+	BPF_JMP32_IMM(BPF_JNE, BPF_REG_2, 8, 5),
+	BPF_JMP_IMM(BPF_JSGE, BPF_REG_2, 500, 2),
+	BPF_MOV64_IMM(BPF_REG_0, 2),
+	BPF_EXIT_INSN(),
+	BPF_MOV64_REG(BPF_REG_0, BPF_REG_4),
+	BPF_EXIT_INSN(),
+	BPF_MOV64_IMM(BPF_REG_0, 1),
+	BPF_EXIT_INSN(),
+	},
+	.prog_type = BPF_PROG_TYPE_SCHED_CLS,
+	.result = ACCEPT,
+	.retval = 1,
+},