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bpf: Populate pairs of btf_id and destructor kfunc in btf

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To support storing referenced PTR_TO_BTF_ID in maps, we require
associating a specific BTF ID with a 'destructor' kfunc. This is because
we need to release a live referenced pointer at a certain offset in map
value from the map destruction path, otherwise we end up leaking
resources.

Hence, introduce support for passing an array of btf_id, kfunc_btf_id
pairs that denote a BTF ID and its associated release function. Then,
add an accessor 'btf_find_dtor_kfunc' which can be used to look up the
destructor kfunc of a certain BTF ID. If found, we can use it to free
the object from the map free path.

The registration of these pairs also serve as a whitelist of structures
which are allowed as referenced PTR_TO_BTF_ID in a BPF map, because
without finding the destructor kfunc, we will bail and return an error.

Signed-off-by: Kumar Kartikeya Dwivedi <memxor@gmail.com>
Signed-off-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/20220424214901.2743946-7-memxor@gmail.com
This commit is contained in:
Kumar Kartikeya Dwivedi
2022-04-25 03:18:54 +05:30
committed by Alexei Starovoitov
parent 4d7d7f69f4
commit 5ce937d613
2 changed files with 125 additions and 0 deletions
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17
include/linux/btf.h
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@@ -40,6 +40,11 @@ struct btf_kfunc_id_set {
};
};
struct btf_id_dtor_kfunc {
u32 btf_id;
u32 kfunc_btf_id;
};
extern const struct file_operations btf_fops;
void btf_get(struct btf *btf);
@@ -346,6 +351,9 @@ bool btf_kfunc_id_set_contains(const struct btf *btf,
enum btf_kfunc_type type, u32 kfunc_btf_id);
int register_btf_kfunc_id_set(enum bpf_prog_type prog_type,
const struct btf_kfunc_id_set *s);
s32 btf_find_dtor_kfunc(struct btf *btf, u32 btf_id);
int register_btf_id_dtor_kfuncs(const struct btf_id_dtor_kfunc *dtors, u32 add_cnt,
struct module *owner);
#else
static inline const struct btf_type *btf_type_by_id(const struct btf *btf,
u32 type_id)
@@ -369,6 +377,15 @@ static inline int register_btf_kfunc_id_set(enum bpf_prog_type prog_type,
{
return 0;
}
static inline s32 btf_find_dtor_kfunc(struct btf *btf, u32 btf_id)
{
return -ENOENT;
}
static inline int register_btf_id_dtor_kfuncs(const struct btf_id_dtor_kfunc *dtors,
u32 add_cnt, struct module *owner)
{
return 0;
}
#endif
#endif