selftests/bpf: test if pointer type is tracked for BPF_ST_MEM

Check that verifier tracks pointer types for BPF_ST_MEM instructions
and reports error if pointer types do not match for different
execution branches.

Signed-off-by: Eduard Zingerman <eddyz87@gmail.com>
Link: https://lore.kernel.org/r/20230304011247.566040-3-eddyz87@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

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

@@ -239,6 +239,29 @@
 	.errstr = "same insn cannot be used with different pointers",
 	.prog_type = BPF_PROG_TYPE_SCHED_CLS,
 },
+{
+	/* Same as above, but use BPF_ST_MEM to save 42
+	 * instead of BPF_STX_MEM.
+	 */
+	"unpriv: spill/fill of different pointers st",
+	.insns = {
+	BPF_ALU64_REG(BPF_MOV, BPF_REG_6, BPF_REG_10),
+	BPF_ALU64_IMM(BPF_ADD, BPF_REG_6, -8),
+	BPF_JMP_IMM(BPF_JEQ, BPF_REG_1, 0, 3),
+	BPF_MOV64_REG(BPF_REG_2, BPF_REG_10),
+	BPF_ALU64_IMM(BPF_ADD, BPF_REG_2, -16),
+	BPF_STX_MEM(BPF_DW, BPF_REG_6, BPF_REG_2, 0),
+	BPF_JMP_IMM(BPF_JNE, BPF_REG_1, 0, 1),
+	BPF_STX_MEM(BPF_DW, BPF_REG_6, BPF_REG_1, 0),
+	BPF_LDX_MEM(BPF_DW, BPF_REG_1, BPF_REG_6, 0),
+	BPF_ST_MEM(BPF_W, BPF_REG_1, offsetof(struct __sk_buff, mark), 42),
+	BPF_MOV64_IMM(BPF_REG_0, 0),
+	BPF_EXIT_INSN(),
+	},
+	.result = REJECT,
+	.errstr = "same insn cannot be used with different pointers",
+	.prog_type = BPF_PROG_TYPE_SCHED_CLS,
+},
 {
 	"unpriv: spill/fill of different pointers stx - ctx and sock",
 	.insns = {