From 9b459804ff9973e173fabafba2a1319f771e85fa Mon Sep 17 00:00:00 2001 From: Lorenz Bauer Date: Mon, 6 Mar 2023 11:21:37 +0000 Subject: [PATCH 1/2] btf: fix resolving BTF_KIND_VAR after ARRAY, STRUCT, UNION, PTR btf_datasec_resolve contains a bug that causes the following BTF to fail loading: [1] DATASEC a size=2 vlen=2 type_id=4 offset=0 size=1 type_id=7 offset=1 size=1 [2] INT (anon) size=1 bits_offset=0 nr_bits=8 encoding=(none) [3] PTR (anon) type_id=2 [4] VAR a type_id=3 linkage=0 [5] INT (anon) size=1 bits_offset=0 nr_bits=8 encoding=(none) [6] TYPEDEF td type_id=5 [7] VAR b type_id=6 linkage=0 This error message is printed during btf_check_all_types: [1] DATASEC a size=2 vlen=2 type_id=7 offset=1 size=1 Invalid type By tracing btf_*_resolve we can pinpoint the problem: btf_datasec_resolve(depth: 1, type_id: 1, mode: RESOLVE_TBD) = 0 btf_var_resolve(depth: 2, type_id: 4, mode: RESOLVE_TBD) = 0 btf_ptr_resolve(depth: 3, type_id: 3, mode: RESOLVE_PTR) = 0 btf_var_resolve(depth: 2, type_id: 4, mode: RESOLVE_PTR) = 0 btf_datasec_resolve(depth: 1, type_id: 1, mode: RESOLVE_PTR) = -22 The last invocation of btf_datasec_resolve should invoke btf_var_resolve by means of env_stack_push, instead it returns EINVAL. The reason is that env_stack_push is never executed for the second VAR. if (!env_type_is_resolve_sink(env, var_type) && !env_type_is_resolved(env, var_type_id)) { env_stack_set_next_member(env, i + 1); return env_stack_push(env, var_type, var_type_id); } env_type_is_resolve_sink() changes its behaviour based on resolve_mode. For RESOLVE_PTR, we can simplify the if condition to the following: (btf_type_is_modifier() || btf_type_is_ptr) && !env_type_is_resolved() Since we're dealing with a VAR the clause evaluates to false. This is not sufficient to trigger the bug however. The log output and EINVAL are only generated if btf_type_id_size() fails. if (!btf_type_id_size(btf, &type_id, &type_size)) { btf_verifier_log_vsi(env, v->t, vsi, "Invalid type"); return -EINVAL; } Most types are sized, so for example a VAR referring to an INT is not a problem. The bug is only triggered if a VAR points at a modifier. Since we skipped btf_var_resolve that modifier was also never resolved, which means that btf_resolved_type_id returns 0 aka VOID for the modifier. This in turn causes btf_type_id_size to return NULL, triggering EINVAL. To summarise, the following conditions are necessary: - VAR pointing at PTR, STRUCT, UNION or ARRAY - Followed by a VAR pointing at TYPEDEF, VOLATILE, CONST, RESTRICT or TYPE_TAG The fix is to reset resolve_mode to RESOLVE_TBD before attempting to resolve a VAR from a DATASEC. Fixes: 1dc92851849c ("bpf: kernel side support for BTF Var and DataSec") Signed-off-by: Lorenz Bauer Link: https://lore.kernel.org/r/20230306112138.155352-2-lmb@isovalent.com Signed-off-by: Martin KaFai Lau --- kernel/bpf/btf.c | 1 + 1 file changed, 1 insertion(+) diff --git a/kernel/bpf/btf.c b/kernel/bpf/btf.c index fa22ec79ac0e1..73780748404c2 100644 --- a/kernel/bpf/btf.c +++ b/kernel/bpf/btf.c @@ -4569,6 +4569,7 @@ static int btf_datasec_resolve(struct btf_verifier_env *env, struct btf *btf = env->btf; u16 i; + env->resolve_mode = RESOLVE_TBD; for_each_vsi_from(i, v->next_member, v->t, vsi) { u32 var_type_id = vsi->type, type_id, type_size = 0; const struct btf_type *var_type = btf_type_by_id(env->btf, From dfdd608c3b365f0fd49d7e13911ebcde06b9865b Mon Sep 17 00:00:00 2001 From: Lorenz Bauer Date: Mon, 6 Mar 2023 11:21:38 +0000 Subject: [PATCH 2/2] selftests/bpf: check that modifier resolves after pointer Add a regression test that ensures that a VAR pointing at a modifier which follows a PTR (or STRUCT or ARRAY) is resolved correctly by the datasec validator. Signed-off-by: Lorenz Bauer Link: https://lore.kernel.org/r/20230306112138.155352-3-lmb@isovalent.com Signed-off-by: Martin KaFai Lau --- tools/testing/selftests/bpf/prog_tests/btf.c | 28 ++++++++++++++++++++ 1 file changed, 28 insertions(+) diff --git a/tools/testing/selftests/bpf/prog_tests/btf.c b/tools/testing/selftests/bpf/prog_tests/btf.c index cbb600be943d3..210d643fda6c7 100644 --- a/tools/testing/selftests/bpf/prog_tests/btf.c +++ b/tools/testing/selftests/bpf/prog_tests/btf.c @@ -879,6 +879,34 @@ static struct btf_raw_test raw_tests[] = { .btf_load_err = true, .err_str = "Invalid elem", }, +{ + .descr = "var after datasec, ptr followed by modifier", + .raw_types = { + /* .bss section */ /* [1] */ + BTF_TYPE_ENC(NAME_TBD, BTF_INFO_ENC(BTF_KIND_DATASEC, 0, 2), + sizeof(void*)+4), + BTF_VAR_SECINFO_ENC(4, 0, sizeof(void*)), + BTF_VAR_SECINFO_ENC(6, sizeof(void*), 4), + /* int */ /* [2] */ + BTF_TYPE_INT_ENC(0, BTF_INT_SIGNED, 0, 32, 4), + /* int* */ /* [3] */ + BTF_TYPE_ENC(0, BTF_INFO_ENC(BTF_KIND_PTR, 0, 0), 2), + BTF_VAR_ENC(NAME_TBD, 3, 0), /* [4] */ + /* const int */ /* [5] */ + BTF_TYPE_ENC(0, BTF_INFO_ENC(BTF_KIND_CONST, 0, 0), 2), + BTF_VAR_ENC(NAME_TBD, 5, 0), /* [6] */ + BTF_END_RAW, + }, + .str_sec = "\0a\0b\0c\0", + .str_sec_size = sizeof("\0a\0b\0c\0"), + .map_type = BPF_MAP_TYPE_ARRAY, + .map_name = ".bss", + .key_size = sizeof(int), + .value_size = sizeof(void*)+4, + .key_type_id = 0, + .value_type_id = 1, + .max_entries = 1, +}, /* Test member exceeds the size of struct. * * struct A {