selftests/bpf: Add variable-length data concat pattern less than test

Extend original variable-length tests with a case to catch a common
existing pattern of testing for < 0 for errors. Note because
verifier also tracks upper bounds and we know it can not be greater
than MAX_LEN here we can skip upper bound check.

In ALU64 enabled compilation converting from long->int return types
in probe helpers results in extra instruction pattern, <<= 32, s >>= 32.
The trade-off is the non-ALU64 case works. If you really care about
every extra insn (XDP case?) then you probably should be using original
int type.

In addition adding a sext insn to bpf might help the verifier in the
general case to avoid these types of tricks.
Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: Andrii Nakryiko <andriin@fb.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Link: https://lore.kernel.org/bpf/20200623032224.4020118-3-andriin@fb.com

tools/testing/selftests/bpf/prog_tests/varlen.c

@@ -51,6 +51,18 @@ void test_varlen(void)
 	CHECK_VAL(data->total2, size1 + size2);
 	CHECK(memcmp(data->payload2, exp_str, size1 + size2), "content_check",
 	      "doesn't match!");
+
+	CHECK_VAL(data->payload3_len1, size1);
+	CHECK_VAL(data->payload3_len2, size2);
+	CHECK_VAL(data->total3, size1 + size2);
+	CHECK(memcmp(data->payload3, exp_str, size1 + size2), "content_check",
+	      "doesn't match!");
+
+	CHECK_VAL(data->payload4_len1, size1);
+	CHECK_VAL(data->payload4_len2, size2);
+	CHECK_VAL(data->total4, size1 + size2);
+	CHECK(memcmp(data->payload4, exp_str, size1 + size2), "content_check",
+	      "doesn't match!");
 cleanup:
 	test_varlen__destroy(skel);
 }

tools/testing/selftests/bpf/progs/test_varlen.c

@@ -26,8 +26,18 @@ int payload2_len2 = -1;
 int total2 = -1;
 char payload2[MAX_LEN + MAX_LEN] = { 1 };
 
+int payload3_len1 = -1;
+int payload3_len2 = -1;
+int total3= -1;
+char payload3[MAX_LEN + MAX_LEN] = { 1 };
+
+int payload4_len1 = -1;
+int payload4_len2 = -1;
+int total4= -1;
+char payload4[MAX_LEN + MAX_LEN] = { 1 };
+
 SEC("raw_tp/sys_enter")
-int handler64(void *regs)
+int handler64_unsigned(void *regs)
 {
 	int pid = bpf_get_current_pid_tgid() >> 32;
 	void *payload = payload1;
@@ -54,8 +64,34 @@ int handler64(void *regs)
 	return 0;
 }
 
-SEC("tp_btf/sys_enter")
-int handler32(void *regs)
+SEC("raw_tp/sys_exit")
+int handler64_signed(void *regs)
+{
+	int pid = bpf_get_current_pid_tgid() >> 32;
+	void *payload = payload3;
+	long len;
+
+	/* ignore irrelevant invocations */
+	if (test_pid != pid || !capture)
+		return 0;
+
+	len = bpf_probe_read_kernel_str(payload, MAX_LEN, &buf_in1[0]);
+	if (len >= 0) {
+		payload += len;
+		payload3_len1 = len;
+	}
+	len = bpf_probe_read_kernel_str(payload, MAX_LEN, &buf_in2[0]);
+	if (len >= 0) {
+		payload += len;
+		payload3_len2 = len;
+	}
+	total3 = payload - (void *)payload3;
+
+	return 0;
+}
+
+SEC("tp/raw_syscalls/sys_enter")
+int handler32_unsigned(void *regs)
 {
 	int pid = bpf_get_current_pid_tgid() >> 32;
 	void *payload = payload2;
@@ -82,7 +118,33 @@ int handler32(void *regs)
 	return 0;
 }
 
-SEC("tp_btf/sys_exit")
+SEC("tp/raw_syscalls/sys_exit")
+int handler32_signed(void *regs)
+{
+	int pid = bpf_get_current_pid_tgid() >> 32;
+	void *payload = payload4;
+	int len;
+
+	/* ignore irrelevant invocations */
+	if (test_pid != pid || !capture)
+		return 0;
+
+	len = bpf_probe_read_kernel_str(payload, MAX_LEN, &buf_in1[0]);
+	if (len >= 0) {
+		payload += len;
+		payload4_len1 = len;
+	}
+	len = bpf_probe_read_kernel_str(payload, MAX_LEN, &buf_in2[0]);
+	if (len >= 0) {
+		payload += len;
+		payload4_len2 = len;
+	}
+	total4 = payload - (void *)payload4;
+
+	return 0;
+}
+
+SEC("tp/syscalls/sys_exit_getpid")
 int handler_exit(void *regs)
 {
 	long bla;