[PATCH bpf-next v1 3/3] selftests/bpf: add test case for userspace and bpf type size mismatch

[Delyan Kratunov <delyank@fb.com>]

Multiple test cases already fail if you add a type whose size is
different between userspace and bpf. That said, let's also add an
explicit test that ensures mis-sized reads/writes do not actually
happen. This test case fails before this patch series and passes after:

test_skeleton:FAIL:writes and reads match size unexpected writes
and reads match size: actual 3735928559 != expected 8030895855
test_skeleton:FAIL:skeleton uses underlying type unexpected
skeleton uses underlying type: actual 8 != expected 4

Signed-off-by: Delyan Kratunov <delyank@fb.com>
---
 tools/testing/selftests/bpf/prog_tests/skeleton.c | 6 ++++++
 tools/testing/selftests/bpf/progs/test_skeleton.c | 8 ++++++++
 2 files changed, 14 insertions(+)

diff --git a/tools/testing/selftests/bpf/prog_tests/skeleton.c b/tools/testing/selftests/bpf/prog_tests/skeleton.c
index 9894e1b39211..bc07da929566 100644
--- a/tools/testing/selftests/bpf/prog_tests/skeleton.c
+++ b/tools/testing/selftests/bpf/prog_tests/skeleton.c
@@ -97,6 +97,9 @@ void test_skeleton(void)

 	skel->data_read_mostly->read_mostly_var = 123;

+	/* validate apparent 64-bit value is actually 32-bit */
+	skel->data->intest64 = (typeof(skel->data->intest64)) 0xdeadbeefdeadbeefULL;
+
 	err = test_skeleton__attach(skel);
 	if (CHECK(err, "skel_attach", "skeleton attach failed: %d\n", err))
 		goto cleanup;
@@ -126,6 +129,9 @@ void test_skeleton(void)
 	ASSERT_OK_PTR(elf_bytes, "elf_bytes");
 	ASSERT_GE(elf_bytes_sz, 0, "elf_bytes_sz");

+	ASSERT_EQ(skel->data->outtest64, skel->data->intest64, "writes and reads match size");
+	ASSERT_EQ(sizeof(skel->data->intest64), sizeof(u32), "skeleton uses underlying type");
+
 cleanup:
 	test_skeleton__destroy(skel);
 }
diff --git a/tools/testing/selftests/bpf/progs/test_skeleton.c b/tools/testing/selftests/bpf/progs/test_skeleton.c
index 1b1187d2967b..fd1f4910cf42 100644
--- a/tools/testing/selftests/bpf/progs/test_skeleton.c
+++ b/tools/testing/selftests/bpf/progs/test_skeleton.c
@@ -16,6 +16,13 @@ struct s {
 int in1 = -1;
 long long in2 = -1;

+/* declare the int64_t type to actually be 32-bit to ensure the skeleton
+ * uses actual sizes and doesn't just copy the type name
+ */
+typedef __s32 int64_t;
+int64_t intest64 = -1;
+int64_t outtest64 = -1;
+
 /* .bss section */
 char in3 = '\0';
 long long in4 __attribute__((aligned(64))) = 0;
@@ -62,6 +69,7 @@ int handler(const void *ctx)
 	out4 = in4;
 	out5 = in5;
 	out6 = in.in6;
+	outtest64 = intest64;

 	bpf_syscall = CONFIG_BPF_SYSCALL;
 	kern_ver = LINUX_KERNEL_VERSION;
--
2.34.1