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bpf: Verify ownership relationships for user BTF types

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Ensure that there can be no ownership cycles among different types by
way of having owning objects that can hold some other type as their
element. For instance, a map value can only hold allocated objects, but
these are allowed to have another bpf_list_head. To prevent unbounded
recursion while freeing resources, elements of bpf_list_head in local
kptrs can never have a bpf_list_head which are part of list in a map
value. Later patches will verify this by having dedicated BTF selftests.

Also, to make runtime destruction easier, once btf_struct_metas is fully
populated, we can stash the metadata of the value type directly in the
metadata of the list_head fields, as that allows easier access to the
value type's layout to destruct it at runtime from the btf_field entry
of the list head itself.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Link: https://lore.kernel.org/r/20221118015614.2013203-8-memxor@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
This commit is contained in:
Kumar Kartikeya Dwivedi
2022-11-18 07:25:57 +05:30
committed by Alexei Starovoitov
parent 8ffa5cc142
commit 865ce09a49
4 changed files with 77 additions and 0 deletions
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include/linux/btf.h
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@@ -178,6 +178,7 @@ int btf_find_spin_lock(const struct btf *btf, const struct btf_type *t);
int btf_find_timer(const struct btf *btf, const struct btf_type *t);
struct btf_record *btf_parse_fields(const struct btf *btf, const struct btf_type *t,
u32 field_mask, u32 value_size);
int btf_check_and_fixup_fields(const struct btf *btf, struct btf_record *rec);
struct btf_field_offs *btf_parse_field_offs(struct btf_record *rec);
bool btf_type_is_void(const struct btf_type *t);
s32 btf_find_by_name_kind(const struct btf *btf, const char *name, u8 kind);