selftests/bpf: Test ambiguous associated struct_ops

Add a test to make sure implicit struct_ops association does not
break backward compatibility nor return incorrect struct_ops.
struct_ops programs should still be allowed to be reused in
different struct_ops map. The associated struct_ops map set implicitly
however will be poisoned. Trying to read it through the helper
bpf_prog_get_assoc_struct_ops() should result in a NULL pointer.

While recursion of test_1() cannot happen due to the associated
struct_ops being ambiguois, explicitly check for it to prevent stack
overflow if the test regresses.

Signed-off-by: Amery Hung <ameryhung@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Link: https://lore.kernel.org/bpf/20251203233748.668365-6-ameryhung@gmail.com

diff --git a/tools/testing/selftests/bpf/prog_tests/test_struct_ops_assoc.c b/tools/testing/selftests/bpf/prog_tests/test_struct_ops_assoc.c
index 1e24a4915524e22a42a752f10ae776ad149b9a9f..02173504f675f32b610ec13c4e97013d3debf6d8 100644 (file)
--- a/tools/testing/selftests/bpf/prog_tests/test_struct_ops_assoc.c
+++ b/tools/testing/selftests/bpf/prog_tests/test_struct_ops_assoc.c
@@ -2,6 +2,7 @@
 
 #include <test_progs.h>
 #include "struct_ops_assoc.skel.h"
+#include "struct_ops_assoc_reuse.skel.h"
 
 static void test_st_ops_assoc(void)
 {
@@ -65,8 +66,45 @@ out:
        struct_ops_assoc__destroy(skel);
 }
 
+static void test_st_ops_assoc_reuse(void)
+{
+       struct struct_ops_assoc_reuse *skel = NULL;
+       int err;
+
+       skel = struct_ops_assoc_reuse__open_and_load();
+       if (!ASSERT_OK_PTR(skel, "struct_ops_assoc_reuse__open"))
+               goto out;
+
+       err = bpf_program__assoc_struct_ops(skel->progs.syscall_prog_a,
+                                           skel->maps.st_ops_map_a, NULL);
+       ASSERT_OK(err, "bpf_program__assoc_struct_ops(syscall_prog_a, st_ops_map_a)");
+
+       err = bpf_program__assoc_struct_ops(skel->progs.syscall_prog_b,
+                                           skel->maps.st_ops_map_b, NULL);
+       ASSERT_OK(err, "bpf_program__assoc_struct_ops(syscall_prog_b, st_ops_map_b)");
+
+       err = struct_ops_assoc_reuse__attach(skel);
+       if (!ASSERT_OK(err, "struct_ops_assoc__attach"))
+               goto out;
+
+       /* run syscall_prog that calls .test_1 and checks return */
+       err = bpf_prog_test_run_opts(bpf_program__fd(skel->progs.syscall_prog_a), NULL);
+       ASSERT_OK(err, "bpf_prog_test_run_opts");
+
+       err = bpf_prog_test_run_opts(bpf_program__fd(skel->progs.syscall_prog_b), NULL);
+       ASSERT_OK(err, "bpf_prog_test_run_opts");
+
+       ASSERT_EQ(skel->bss->test_err_a, 0, "skel->bss->test_err_a");
+       ASSERT_EQ(skel->bss->test_err_b, 0, "skel->bss->test_err_b");
+
+out:
+       struct_ops_assoc_reuse__destroy(skel);
+}
+
 void test_struct_ops_assoc(void)
 {
        if (test__start_subtest("st_ops_assoc"))
                test_st_ops_assoc();
+       if (test__start_subtest("st_ops_assoc_reuse"))
+               test_st_ops_assoc_reuse();
 }

diff --git a/tools/testing/selftests/bpf/progs/struct_ops_assoc_reuse.c b/tools/testing/selftests/bpf/progs/struct_ops_assoc_reuse.c
new file mode 100644 (file)
index 0000000..5bb6ebf
--- /dev/null
+++ b/tools/testing/selftests/bpf/progs/struct_ops_assoc_reuse.c
@@ -0,0 +1,75 @@
+// SPDX-License-Identifier: GPL-2.0
+
+#include <vmlinux.h>
+#include <bpf/bpf_tracing.h>
+#include "bpf_misc.h"
+#include "../test_kmods/bpf_testmod.h"
+#include "../test_kmods/bpf_testmod_kfunc.h"
+
+char _license[] SEC("license") = "GPL";
+
+#define MAP_A_MAGIC 1234
+int test_err_a;
+int recur;
+
+/*
+ * test_1_a is reused. The kfunc should not be able to get the associated
+ * struct_ops and call test_1 recursively as it is ambiguous.
+ */
+SEC("struct_ops")
+int BPF_PROG(test_1_a, struct st_ops_args *args)
+{
+       int ret;
+
+       if (!recur) {
+               recur++;
+               ret = bpf_kfunc_multi_st_ops_test_1_impl(args, NULL);
+               if (ret != -1)
+                       test_err_a++;
+               recur--;
+       }
+
+       return MAP_A_MAGIC;
+}
+
+/* Programs associated with st_ops_map_a */
+
+SEC("syscall")
+int syscall_prog_a(void *ctx)
+{
+       struct st_ops_args args = {};
+       int ret;
+
+       ret = bpf_kfunc_multi_st_ops_test_1_impl(&args, NULL);
+       if (ret != MAP_A_MAGIC)
+               test_err_a++;
+
+       return 0;
+}
+
+SEC(".struct_ops.link")
+struct bpf_testmod_multi_st_ops st_ops_map_a = {
+       .test_1 = (void *)test_1_a,
+};
+
+/* Programs associated with st_ops_map_b */
+
+int test_err_b;
+
+SEC("syscall")
+int syscall_prog_b(void *ctx)
+{
+       struct st_ops_args args = {};
+       int ret;
+
+       ret = bpf_kfunc_multi_st_ops_test_1_impl(&args, NULL);
+       if (ret != MAP_A_MAGIC)
+               test_err_b++;
+
+       return 0;
+}
+
+SEC(".struct_ops.link")
+struct bpf_testmod_multi_st_ops st_ops_map_b = {
+       .test_1 = (void *)test_1_a,
+};