tools/bpf: Add verifier tests for 32bit pointer/scalar arithmetic

Added two test_verifier subtests for 32bit pointer/scalar arithmetic
with BPF_SUB operator. They are passing verifier now.
Signed-off-by: Yonghong Song <yhs@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20200618234632.3321367-1-yhs@fb.com

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

@@ -836,3 +836,41 @@
 	.errstr = "R0 invalid mem access 'inv'",
 	.errstr_unpriv = "R0 pointer -= pointer prohibited",
 },
+{
+	"32bit pkt_ptr -= scalar",
+	.insns = {
+	BPF_LDX_MEM(BPF_W, BPF_REG_8, BPF_REG_1,
+		    offsetof(struct __sk_buff, data_end)),
+	BPF_LDX_MEM(BPF_W, BPF_REG_7, BPF_REG_1,
+		    offsetof(struct __sk_buff, data)),
+	BPF_MOV64_REG(BPF_REG_6, BPF_REG_7),
+	BPF_ALU64_IMM(BPF_ADD, BPF_REG_6, 40),
+	BPF_JMP_REG(BPF_JGT, BPF_REG_6, BPF_REG_8, 2),
+	BPF_ALU32_REG(BPF_MOV, BPF_REG_4, BPF_REG_7),
+	BPF_ALU32_REG(BPF_SUB, BPF_REG_6, BPF_REG_4),
+	BPF_MOV64_IMM(BPF_REG_0, 0),
+	BPF_EXIT_INSN(),
+	},
+	.prog_type = BPF_PROG_TYPE_SCHED_CLS,
+	.result = ACCEPT,
+	.flags = F_NEEDS_EFFICIENT_UNALIGNED_ACCESS,
+},
+{
+	"32bit scalar -= pkt_ptr",
+	.insns = {
+	BPF_LDX_MEM(BPF_W, BPF_REG_8, BPF_REG_1,
+		    offsetof(struct __sk_buff, data_end)),
+	BPF_LDX_MEM(BPF_W, BPF_REG_7, BPF_REG_1,
+		    offsetof(struct __sk_buff, data)),
+	BPF_MOV64_REG(BPF_REG_6, BPF_REG_7),
+	BPF_ALU64_IMM(BPF_ADD, BPF_REG_6, 40),
+	BPF_JMP_REG(BPF_JGT, BPF_REG_6, BPF_REG_8, 2),
+	BPF_ALU32_REG(BPF_MOV, BPF_REG_4, BPF_REG_6),
+	BPF_ALU32_REG(BPF_SUB, BPF_REG_4, BPF_REG_7),
+	BPF_MOV64_IMM(BPF_REG_0, 0),
+	BPF_EXIT_INSN(),
+	},
+	.prog_type = BPF_PROG_TYPE_SCHED_CLS,
+	.result = ACCEPT,
+	.flags = F_NEEDS_EFFICIENT_UNALIGNED_ACCESS,
+},