It is guaranteed that for modifiers, clang always places type tags before other modifiers, and then the base type. We would like to rely on this guarantee inside the kernel to make it simple to parse type tags from BTF. However, a user would be allowed to construct a BTF without such guarantees. Hence, add a pass to check that in modifier chains, type tags only occur at the head of the chain, and then don't occur later in the chain. If we see a type tag, we can have one or more type tags preceding other modifiers that then never have another type tag. If we see other modifiers, all modifiers following them should never be a type tag. Instead of having to walk chains we verified previously, we can remember the last good modifier type ID which headed a good chain. At that point, we must have verified all other chains headed by type IDs less than it. This makes the verification process less costly, and it becomes a simple O(n) pass.
Unified · Split
| @@ -4541,6 +4541,48 @@ static int btf_parse_hdr(struct btf_verifier_env *env) · 4540 unmodified lines | |||
| 4541 | return 0; | 4541 | return 0; |
| 4542 | } | 4542 | } |
| 4543 | 4543 | ||
| 4544 | static int btf_check_type_tags(struct btf_verifier_env *env, | ||
| 4545 | struct btf *btf, int start_id) | ||
| 4546 | { | ||
| 4547 | int i, n, good_id = start_id - 1; | ||
| 4548 | bool in_tags; | ||
| 4549 | |||
| 4550 | n = btf_nr_types(btf); | ||
| 4551 | for (i = start_id; i < n; i++) { | ||
| 4552 | const struct btf_type *t; | ||
| 4553 | u32 cur_id = i; | ||
| 4554 | |||
| 4555 | t = btf_type_by_id(btf, i); | ||
| 4556 | if (!t) | ||
| 4557 | return -EINVAL; | ||
| 4558 | if (!btf_type_is_modifier(t)) | ||
| 4559 | continue; | ||
| 4560 | |||
| 4561 | cond_resched(); | ||
| 4562 | |||
| 4563 | in_tags = btf_type_is_type_tag(t); | ||
| 4564 | while (btf_type_is_modifier(t)) { | ||
| 4565 | if (btf_type_is_type_tag(t)) { | ||
| 4566 | if (!in_tags) { | ||
| 4567 | btf_verifier_log(env, "Type tags don't precede modifiers"); | ||
| 4568 | return -EINVAL; | ||
| 4569 | } | ||
| 4570 | } else if (in_tags) { | ||
| 4571 | in_tags = false; | ||
| 4572 | } | ||
| 4573 | if (cur_id <= good_id) | ||
| 4574 | break; | ||
| 4575 | /* Move to next type */ | ||
| 4576 | cur_id = t->type; | ||
| 4577 | t = btf_type_by_id(btf, cur_id); | ||
| 4578 | if (!t) | ||
| 4579 | return -EINVAL; | ||
| 4580 | } | ||
| 4581 | good_id = i; | ||
| 4582 | } | ||
| 4583 | return 0; | ||
| 4584 | } | ||
| 4585 | |||
| 4544 | static struct btf *btf_parse(bpfptr_t btf_data, u32 btf_data_size, | 4586 | static struct btf *btf_parse(bpfptr_t btf_data, u32 btf_data_size, |
| 4545 | u32 log_level, char __user *log_ubuf, u32 log_size) | 4587 | u32 log_level, char __user *log_ubuf, u32 log_size) |
| 4546 | { | 4588 | { |
| @@ -4608,6 +4650,10 @@ static struct btf *btf_parse(bpfptr_t btf_data, u32 btf_data_size, · 61 unmodified lines | |||
| 4608 | if (err) | 4650 | if (err) |
| 4609 | goto errout; | 4651 | goto errout; |
| 4610 | 4652 | ||
| 4653 | err = btf_check_type_tags(env, btf, 1); | ||
| 4654 | if (err) | ||
| 4655 | goto errout; | ||
| 4656 | |||
| 4611 | if (log->level && bpf_verifier_log_full(log)) { | 4657 | if (log->level && bpf_verifier_log_full(log)) { |
| 4612 | err = -ENOSPC; | 4658 | err = -ENOSPC; |
| 4613 | goto errout; | 4659 | goto errout; |
| @@ -4809,6 +4855,10 @@ struct btf *btf_parse_vmlinux(void) · 195 unmodified lines | |||
| 4809 | if (err) | 4855 | if (err) |
| 4810 | goto errout; | 4856 | goto errout; |
| 4811 | 4857 | ||
| 4858 | err = btf_check_type_tags(env, btf, 1); | ||
| 4859 | if (err) | ||
| 4860 | goto errout; | ||
| 4861 | |||
| 4812 | /* btf_parse_vmlinux() runs under bpf_verifier_lock */ | 4862 | /* btf_parse_vmlinux() runs under bpf_verifier_lock */ |
| 4813 | bpf_ctx_convert.t = btf_type_by_id(btf, bpf_ctx_convert_btf_id[0]); | 4863 | bpf_ctx_convert.t = btf_type_by_id(btf, bpf_ctx_convert_btf_id[0]); |
| 4814 | 4864 | ||
| @@ -4894,6 +4944,10 @@ static struct btf *btf_parse_module(const char *module_name, const void *data, u · 79 unmodified lines | |||
| 4894 | if (err) | 4944 | if (err) |
| 4895 | goto errout; | 4945 | goto errout; |
| 4896 | 4946 | ||
| 4947 | err = btf_check_type_tags(env, btf, btf_nr_types(base_btf)); | ||
| 4948 | if (err) | ||
| 4949 | goto errout; | ||
| 4950 | |||
| 4897 | btf_verifier_env_free(env); | 4951 | btf_verifier_env_free(env); |
| 4898 | refcount_set(&btf->refcnt, 1); | 4952 | refcount_set(&btf->refcnt, 1); |
| 4899 | return btf; | 4953 | return btf; |