From c911fc61a7ce367f9ea48e457f31bb171e80ca4d Mon Sep 17 00:00:00 2001 From: Kui-Feng Lee Date: Wed, 13 Mar 2024 14:41:37 -0700 Subject: [PATCH 1/2] libbpf: Skip zeroed or null fields if not found in the kernel type. Accept additional fields of a struct_ops type with all zero values even if these fields are not in the corresponding type in the kernel. This provides a way to be backward compatible. User space programs can use the same map on a machine running an old kernel by clearing fields that do not exist in the kernel. Signed-off-by: Kui-Feng Lee Signed-off-by: Andrii Nakryiko Link: https://lore.kernel.org/bpf/20240313214139.685112-2-thinker.li@gmail.com --- tools/lib/bpf/libbpf.c | 24 +++++++++++++++++++----- 1 file changed, 19 insertions(+), 5 deletions(-) diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c index 124883eaa0cf..604368cfbf02 100644 --- a/tools/lib/bpf/libbpf.c +++ b/tools/lib/bpf/libbpf.c @@ -1132,8 +1132,26 @@ static int bpf_map__init_kern_struct_ops(struct bpf_map *map) const char *mname; mname = btf__name_by_offset(btf, member->name_off); + moff = member->offset / 8; + mdata = data + moff; + msize = btf__resolve_size(btf, member->type); + if (msize < 0) { + pr_warn("struct_ops init_kern %s: failed to resolve the size of member %s\n", + map->name, mname); + return msize; + } + kern_member = find_member_by_name(kern_btf, kern_type, mname); if (!kern_member) { + /* Skip all zeros or null fields if they are not + * presented in the kernel BTF. + */ + if (libbpf_is_mem_zeroed(mdata, msize)) { + pr_info("struct_ops %s: member %s not found in kernel, skipping it as it's set to zero\n", + map->name, mname); + continue; + } + pr_warn("struct_ops init_kern %s: Cannot find member %s in kernel BTF\n", map->name, mname); return -ENOTSUP; @@ -1147,10 +1165,7 @@ static int bpf_map__init_kern_struct_ops(struct bpf_map *map) return -ENOTSUP; } - moff = member->offset / 8; kern_moff = kern_member->offset / 8; - - mdata = data + moff; kern_mdata = kern_data + kern_moff; mtype = skip_mods_and_typedefs(btf, member->type, &mtype_id); @@ -1230,9 +1245,8 @@ static int bpf_map__init_kern_struct_ops(struct bpf_map *map) continue; } - msize = btf__resolve_size(btf, mtype_id); kern_msize = btf__resolve_size(kern_btf, kern_mtype_id); - if (msize < 0 || kern_msize < 0 || msize != kern_msize) { + if (kern_msize < 0 || msize != kern_msize) { pr_warn("struct_ops init_kern %s: Error in size of member %s: %zd != %zd(kernel)\n", map->name, mname, (ssize_t)msize, (ssize_t)kern_msize); From 26a7cf2bbea656837583f9a1a0f9390db63d6cc3 Mon Sep 17 00:00:00 2001 From: Kui-Feng Lee Date: Wed, 13 Mar 2024 14:41:38 -0700 Subject: [PATCH 2/2] selftests/bpf: Ensure libbpf skip all-zeros fields of struct_ops maps. A new version of a type may have additional fields that do not exist in older versions. Previously, libbpf would reject struct_ops maps with a new version containing extra fields when running on a machine with an old kernel. However, we have updated libbpf to ignore these fields if their values are all zeros or null in order to provide backward compatibility. Signed-off-by: Kui-Feng Lee Signed-off-by: Andrii Nakryiko Link: https://lore.kernel.org/bpf/20240313214139.685112-3-thinker.li@gmail.com --- .../bpf/prog_tests/test_struct_ops_module.c | 47 +++++++++++++++++++ .../selftests/bpf/progs/struct_ops_module.c | 16 ++++++- 2 files changed, 62 insertions(+), 1 deletion(-) diff --git a/tools/testing/selftests/bpf/prog_tests/test_struct_ops_module.c b/tools/testing/selftests/bpf/prog_tests/test_struct_ops_module.c index ee5372c7f2c7..098776d00ab4 100644 --- a/tools/testing/selftests/bpf/prog_tests/test_struct_ops_module.c +++ b/tools/testing/selftests/bpf/prog_tests/test_struct_ops_module.c @@ -93,9 +93,56 @@ static void test_struct_ops_load(void) struct_ops_module__destroy(skel); } +static void test_struct_ops_not_zeroed(void) +{ + struct struct_ops_module *skel; + int err; + + /* zeroed is 0, and zeroed_op is null */ + skel = struct_ops_module__open(); + if (!ASSERT_OK_PTR(skel, "struct_ops_module_open")) + return; + + err = struct_ops_module__load(skel); + ASSERT_OK(err, "struct_ops_module_load"); + + struct_ops_module__destroy(skel); + + /* zeroed is not 0 */ + skel = struct_ops_module__open(); + if (!ASSERT_OK_PTR(skel, "struct_ops_module_open_not_zeroed")) + return; + + /* libbpf should reject the testmod_zeroed since struct + * bpf_testmod_ops in the kernel has no "zeroed" field and the + * value of "zeroed" is non-zero. + */ + skel->struct_ops.testmod_zeroed->zeroed = 0xdeadbeef; + err = struct_ops_module__load(skel); + ASSERT_ERR(err, "struct_ops_module_load_not_zeroed"); + + struct_ops_module__destroy(skel); + + /* zeroed_op is not null */ + skel = struct_ops_module__open(); + if (!ASSERT_OK_PTR(skel, "struct_ops_module_open_not_zeroed_op")) + return; + + /* libbpf should reject the testmod_zeroed since the value of its + * "zeroed_op" is not null. + */ + skel->struct_ops.testmod_zeroed->zeroed_op = skel->progs.test_3; + err = struct_ops_module__load(skel); + ASSERT_ERR(err, "struct_ops_module_load_not_zeroed_op"); + + struct_ops_module__destroy(skel); +} + void serial_test_struct_ops_module(void) { if (test__start_subtest("test_struct_ops_load")) test_struct_ops_load(); + if (test__start_subtest("test_struct_ops_not_zeroed")) + test_struct_ops_not_zeroed(); } diff --git a/tools/testing/selftests/bpf/progs/struct_ops_module.c b/tools/testing/selftests/bpf/progs/struct_ops_module.c index 026cabfa7f1f..86e1e50c5531 100644 --- a/tools/testing/selftests/bpf/progs/struct_ops_module.c +++ b/tools/testing/selftests/bpf/progs/struct_ops_module.c @@ -23,7 +23,7 @@ void BPF_PROG(test_2, int a, int b) test_2_result = a + b; } -SEC("struct_ops/test_3") +SEC("?struct_ops/test_3") int BPF_PROG(test_3, int a, int b) { test_2_result = a + b + 3; @@ -54,3 +54,17 @@ struct bpf_testmod_ops___v2 testmod_2 = { .test_1 = (void *)test_1, .test_2 = (void *)test_2_v2, }; + +struct bpf_testmod_ops___zeroed { + int (*test_1)(void); + void (*test_2)(int a, int b); + int (*test_maybe_null)(int dummy, struct task_struct *task); + void (*zeroed_op)(int a, int b); + int zeroed; +}; + +SEC(".struct_ops.link") +struct bpf_testmod_ops___zeroed testmod_zeroed = { + .test_1 = (void *)test_1, + .test_2 = (void *)test_2_v2, +};