[PATCH bpf-next v4 9/9] selftests/bpf: Test trampolines on more BPF functions with stack args

[Yonghong Song <yonghong.song@linux.dev>]

Add two functions to the BPF target program of the int128_tgt_prog test.

callee_split() takes a struct holding an __int128 after five u64s, so
on x86-64 it is passed split between r9 and the stack. fentry and fexit
programs check that the trampoline takes it from there and hands it back
there.

callee_unreliable() takes six u64-sized arguments, the first a plain
pointer, which makes its BTF unreliable while the sixth is still passed
on the stack. The new tgt_prog_unreliable subtest checks that an fentry
program cannot be attached to it.

Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
---
 .../selftests/bpf/prog_tests/tracing_struct.c | 62 +++++++++++++++++++
 .../bpf/progs/tracing_struct_int128_tgt.c     | 32 +++++++++-
 .../bpf/progs/tracing_struct_int128_tracer.c  | 27 ++++++++
 3 files changed, 120 insertions(+), 1 deletion(-)

diff --git a/tools/testing/selftests/bpf/prog_tests/tracing_struct.c b/tools/testing/selftests/bpf/prog_tests/tracing_struct.c
index a02731bc6573..de358f335d98 100644
--- a/tools/testing/selftests/bpf/prog_tests/tracing_struct.c
+++ b/tools/testing/selftests/bpf/prog_tests/tracing_struct.c
@@ -194,9 +194,15 @@ static void test_int128_tgt_prog(void)
 							     "callee_stack");
 		err = err ?: bpf_program__set_attach_target(tracer->progs.stack_exit, fd,
 							     "callee_stack");
+		err = err ?: bpf_program__set_attach_target(tracer->progs.split_entry, fd,
+							     "callee_split");
+		err = err ?: bpf_program__set_attach_target(tracer->progs.split_exit, fd,
+							     "callee_split");
 	} else {
 		bpf_program__set_autoload(tracer->progs.stack_entry, false);
 		bpf_program__set_autoload(tracer->progs.stack_exit, false);
+		bpf_program__set_autoload(tracer->progs.split_entry, false);
+		bpf_program__set_autoload(tracer->progs.split_exit, false);
 	}
 	if (!ASSERT_OK(err, "set_attach_target"))
 		goto out;
@@ -226,6 +232,13 @@ static void test_int128_tgt_prog(void)
 		ASSERT_EQ(tracer->bss->stack_i, 10, "stack:i");
 		ASSERT_EQ(tgt->bss->ret_stack, 385, "stack ret");
 		ASSERT_EQ(tracer->bss->stack_ret, 385, "stack fexit ret");
+
+		ASSERT_EQ(tracer->bss->split_e, 5, "split:e");
+		ASSERT_EQ(tracer->bss->split_lo, 8, "split:h.lo");
+		ASSERT_EQ(tracer->bss->split_hi, 9, "split:h.hi");
+		ASSERT_EQ(tracer->bss->split_i, 10, "split:i");
+		ASSERT_EQ(tgt->bss->ret_split, 246, "split ret");
+		ASSERT_EQ(tracer->bss->split_ret, 246, "split fexit ret");
 	}
 
 out:
@@ -236,6 +249,53 @@ static void test_int128_tgt_prog(void)
 #endif
 }
 
+/*
+ * A static function whose BTF is unreliable gets a trampoline that only knows
+ * of the register arguments, so one taking stack arguments must be refused.
+ */
+static void test_tgt_prog_unreliable(void)
+{
+#if defined(__x86_64__) || defined(__aarch64__)
+	struct tracing_struct_int128_tracer *tracer = NULL;
+	struct tracing_struct_int128_tgt *tgt;
+	char log_buf[4096] = {};
+	struct bpf_program *prog;
+	int err, fd;
+
+	tgt = tracing_struct_int128_tgt__open_and_load();
+	if (!ASSERT_OK_PTR(tgt, "tgt__open_and_load"))
+		return;
+	if (!tgt->rodata->has_stack_arg) {
+		test__skip();
+		goto out;
+	}
+	fd = bpf_program__fd(tgt->progs.run);
+
+	tracer = tracing_struct_int128_tracer__open();
+	if (!ASSERT_OK_PTR(tracer, "tracer__open"))
+		goto out;
+
+	bpf_object__for_each_program(prog, tracer->obj)
+		bpf_program__set_autoload(prog, false);
+	bpf_program__set_autoload(tracer->progs.unreliable_entry, true);
+	bpf_program__set_log_buf(tracer->progs.unreliable_entry, log_buf, sizeof(log_buf));
+	err = bpf_program__set_attach_target(tracer->progs.unreliable_entry, fd,
+					     "callee_unreliable");
+	if (!ASSERT_OK(err, "set_attach_target"))
+		goto out;
+
+	err = tracing_struct_int128_tracer__load(tracer);
+	ASSERT_ERR(err, "tracer__load");
+	ASSERT_HAS_SUBSTR(log_buf, "unreliable BTF and stack arguments", "log");
+
+out:
+	tracing_struct_int128_tracer__destroy(tracer);
+	tracing_struct_int128_tgt__destroy(tgt);
+#else
+	test__skip();
+#endif
+}
+
 /*
  * A trampoline on a function of a tail_call_reachable program keeps the tail
  * call counter pointer on its stack, and has to hand the function its stack
@@ -328,6 +388,8 @@ void test_tracing_struct(void)
 		test_int128_args();
 	if (test__start_subtest("int128_tgt_prog"))
 		test_int128_tgt_prog();
+	if (test__start_subtest("tgt_prog_unreliable"))
+		test_tgt_prog_unreliable();
 	if (test__start_subtest("stack_arg_tailcall"))
 		test_stack_arg_tailcall();
 	if (test__start_subtest("union_args"))
diff --git a/tools/testing/selftests/bpf/progs/tracing_struct_int128_tgt.c b/tools/testing/selftests/bpf/progs/tracing_struct_int128_tgt.c
index 60e997470b59..2561422c25dd 100644
--- a/tools/testing/selftests/bpf/progs/tracing_struct_int128_tgt.c
+++ b/tools/testing/selftests/bpf/progs/tracing_struct_int128_tgt.c
@@ -8,7 +8,7 @@ struct int128_arg {
 };
 
 __u64 base;
-__u64 ret_odd, ret_stack;
+__u64 ret_odd, ret_stack, ret_split, ret_unreliable;
 
 #if defined(__clang__)
 
@@ -46,6 +46,28 @@ static __noinline __u64 callee_stack(__u64 a, __u64 b, __u64 c, __u64 d,
 	       i * 10;
 }
 
+/*
+ * x86-64 BPF code passes h split between r9 and its first stack slot;
+ * arm64 passes it in x5 and x6, so nothing is split there.
+ */
+static __noinline __u64 callee_split(__u64 a, __u64 b, __u64 c, __u64 d,
+				     __u64 e, struct int128_arg h, __u64 i)
+{
+	return a + b * 2 + c * 3 + d * 4 + e * 5 + (__u64)h.v * 6 +
+	       (__u64)((unsigned __int128)h.v >> 64) * 7 + i * 8;
+}
+
+/*
+ * A plain pointer makes the BTF of a static function unreliable, but f is
+ * still passed on the stack. The store keeps p a pointer.
+ */
+static __noinline __u64 callee_unreliable(__u64 *p, __u64 b, __u64 c, __u64 d,
+					  __u64 e, __u64 f)
+{
+	*p += 1;
+	return *p + b * 2 + c * 3 + d * 4 + e * 5 + f * 6;
+}
+
 #else
 
 const volatile bool has_stack_arg = false;
@@ -63,6 +85,14 @@ int run(void *ctx)
 	defined(__BPF_FEATURE_STACK_ARGUMENT)
 	ret_stack = callee_stack(base + 1, base + 2, base + 3, base + 4,
 				 base + 5, base + 6, base + 7, v, base + 10);
+	ret_split = callee_split(base + 1, base + 2, base + 3, base + 4,
+				 base + 5, v, base + 10);
+	{
+		__u64 x = base;
+
+		ret_unreliable = callee_unreliable(&x, base + 2, base + 3,
+						   base + 4, base + 5, base + 6);
+	}
 #endif
 #endif
 	return 0;
diff --git a/tools/testing/selftests/bpf/progs/tracing_struct_int128_tracer.c b/tools/testing/selftests/bpf/progs/tracing_struct_int128_tracer.c
index 5843dc5af9cf..fc81c2eea4a8 100644
--- a/tools/testing/selftests/bpf/progs/tracing_struct_int128_tracer.c
+++ b/tools/testing/selftests/bpf/progs/tracing_struct_int128_tracer.c
@@ -47,4 +47,31 @@ int stack_exit(unsigned long long *ctx)
 	return 0;
 }
 
+long split_e, split_lo, split_hi, split_i, split_ret;
+
+SEC("fentry/callee_split")
+int BPF_PROG2(split_entry, __u64, a, __u64, b, __u64, c, __u64, d, __u64, e,
+	      struct int128_arg, h, __u64, i)
+{
+	split_e = e;
+	split_lo = (__u64)h.v;
+	split_hi = (unsigned __int128)h.v >> 64;
+	split_i = i;
+	return 0;
+}
+
+SEC("fexit/callee_split")
+int split_exit(unsigned long long *ctx)
+{
+	split_ret = ctx[8];
+	return 0;
+}
+
+/* Refused: the trampoline would lose the stack argument. */
+SEC("?fentry/callee_unreliable")
+int unreliable_entry(unsigned long long *ctx)
+{
+	return 0;
+}
+
 char _license[] SEC("license") = "GPL";
-- 
2.53.0-Meta