From f263336a41da287c5aebd35be8f1e0422e49bc5c Mon Sep 17 00:00:00 2001 From: Alan Maguire Date: Wed, 30 Apr 2025 14:42:49 +0100 Subject: [PATCH] selftests/bpf: Add btf dedup test covering module BTF dedup Recently issues were observed with module BTF deduplication failures [1]. Add a dedup selftest that ensures that core kernel types are referenced from split BTF as base BTF types. To do this use bpf_testmod functions which utilize core kernel types, specifically ssize_t bpf_testmod_test_write(struct file *file, struct kobject *kobj, struct bin_attribute *bin_attr, char *buf, loff_t off, size_t len); __bpf_kfunc struct sock *bpf_kfunc_call_test3(struct sock *sk); __bpf_kfunc void bpf_kfunc_call_test_pass_ctx(struct __sk_buff *skb); For each of these ensure that the types they reference - struct file, struct kobject, struct bin_attr etc - are in base BTF. Note that because bpf_testmod.ko is built with distilled base BTF the associated reference types - i.e. the PTR that points at a "struct file" - will be in split BTF. As a result the test resolves typedef and pointer references and verifies the pointed-at or typedef'ed type is in base BTF. Because we use BTF from /sys/kernel/btf/bpf_testmod relocation has occurred for the referenced types and they will be base - not distilled base - types. For large-scale dedup issues, we see such types appear in split BTF and as a result this test fails. Hence it is proposed as a test which will fail when large-scale dedup issues have occurred. [1] https://lore.kernel.org/dwarves/CAADnVQL+-LiJGXwxD3jEUrOonO-fX0SZC8496dVzUXvfkB7gYQ@mail.gmail.com/ Signed-off-by: Alan Maguire Signed-off-by: Andrii Nakryiko Acked-by: Eduard Zingerman Link: https://lore.kernel.org/bpf/20250430134249.2451066-1-alan.maguire@oracle.com --- .../bpf/prog_tests/btf_dedup_split.c | 101 ++++++++++++++++++ 1 file changed, 101 insertions(+) diff --git a/tools/testing/selftests/bpf/prog_tests/btf_dedup_split.c b/tools/testing/selftests/bpf/prog_tests/btf_dedup_split.c index d9024c7a892a..5bc15bb6b7ce 100644 --- a/tools/testing/selftests/bpf/prog_tests/btf_dedup_split.c +++ b/tools/testing/selftests/bpf/prog_tests/btf_dedup_split.c @@ -440,6 +440,105 @@ cleanup: btf__free(btf1); } +/* Ensure module split BTF dedup worked correctly; when dedup fails badly + * core kernel types are in split BTF also, so ensure that references to + * such types point at base - not split - BTF. + * + * bpf_testmod_test_write() has multiple core kernel type parameters; + * + * ssize_t + * bpf_testmod_test_write(struct file *file, struct kobject *kobj, + * struct bin_attribute *bin_attr, + * char *buf, loff_t off, size_t len); + * + * Ensure each of the FUNC_PROTO params is a core kernel type. + * + * Do the same for + * + * __bpf_kfunc struct sock *bpf_kfunc_call_test3(struct sock *sk); + * + * ...and + * + * __bpf_kfunc void bpf_kfunc_call_test_pass_ctx(struct __sk_buff *skb); + * + */ +const char *mod_funcs[] = { + "bpf_testmod_test_write", + "bpf_kfunc_call_test3", + "bpf_kfunc_call_test_pass_ctx" +}; + +static void test_split_module(void) +{ + struct btf *vmlinux_btf, *btf1 = NULL; + int i, nr_base_types; + + vmlinux_btf = btf__load_vmlinux_btf(); + if (!ASSERT_OK_PTR(vmlinux_btf, "vmlinux_btf")) + return; + nr_base_types = btf__type_cnt(vmlinux_btf); + if (!ASSERT_GT(nr_base_types, 0, "nr_base_types")) + goto cleanup; + + btf1 = btf__parse_split("/sys/kernel/btf/bpf_testmod", vmlinux_btf); + if (!ASSERT_OK_PTR(btf1, "split_btf")) + return; + + for (i = 0; i < ARRAY_SIZE(mod_funcs); i++) { + const struct btf_param *p; + const struct btf_type *t; + __u16 vlen; + __u32 id; + int j; + + id = btf__find_by_name_kind(btf1, mod_funcs[i], BTF_KIND_FUNC); + if (!ASSERT_GE(id, nr_base_types, "func_id")) + goto cleanup; + t = btf__type_by_id(btf1, id); + if (!ASSERT_OK_PTR(t, "func_id_type")) + goto cleanup; + t = btf__type_by_id(btf1, t->type); + if (!ASSERT_OK_PTR(t, "func_proto_id_type")) + goto cleanup; + if (!ASSERT_EQ(btf_is_func_proto(t), true, "is_func_proto")) + goto cleanup; + vlen = btf_vlen(t); + + for (j = 0, p = btf_params(t); j < vlen; j++, p++) { + /* bpf_testmod uses resilient split BTF, so any + * reference types will be added to split BTF and their + * associated targets will be base BTF types; for example + * for a "struct sock *" the PTR will be in split BTF + * while the "struct sock" will be in base. + * + * In some cases like loff_t we have to resolve + * multiple typedefs hence the while() loop below. + * + * Note that resilient split BTF generation depends + * on pahole version, so we do not assert that + * reference types are in split BTF, as if pahole + * does not support resilient split BTF they will + * also be base BTF types. + */ + id = p->type; + do { + t = btf__type_by_id(btf1, id); + if (!ASSERT_OK_PTR(t, "param_ref_type")) + goto cleanup; + if (!btf_is_mod(t) && !btf_is_ptr(t) && !btf_is_typedef(t)) + break; + id = t->type; + } while (true); + + if (!ASSERT_LT(id, nr_base_types, "verify_base_type")) + goto cleanup; + } + } +cleanup: + btf__free(btf1); + btf__free(vmlinux_btf); +} + void test_btf_dedup_split() { if (test__start_subtest("split_simple")) @@ -450,4 +549,6 @@ void test_btf_dedup_split() test_split_fwd_resolve(); if (test__start_subtest("split_dup_struct_in_cu")) test_split_dup_struct_in_cu(); + if (test__start_subtest("split_module")) + test_split_module(); } -- 2.50.1