Re: [PATCH bpf-next v13 07/14] bpf: pass attached BTF to the bpf_struct_ops subsystem

[Kui-Feng Lee <sinquersw@gmail.com>]

On 12/15/23 16:19, Martin KaFai Lau wrote:
> On 12/15/23 2:10 PM, Kui-Feng Lee wrote:
>>
>>
>> On 12/14/23 18:44, Martin KaFai Lau wrote:
>>> On 12/8/23 4:27 PM, thinker.li@gmail.com wrote:
>>>> @@ -681,15 +682,30 @@ static struct bpf_map 
>>>> *bpf_struct_ops_map_alloc(union bpf_attr *attr)
>>>>       struct bpf_struct_ops_map *st_map;
>>>>       const struct btf_type *t, *vt;
>>>>       struct bpf_map *map;
>>>> +    struct btf *btf;
>>>>       int ret;
>>>> -    st_ops_desc = bpf_struct_ops_find_value(btf_vmlinux, 
>>>> attr->btf_vmlinux_value_type_id);
>>>> -    if (!st_ops_desc)
>>>> -        return ERR_PTR(-ENOTSUPP);
>>>> +    if (attr->value_type_btf_obj_fd) {
>>>> +        /* The map holds btf for its whole life time. */
>>>> +        btf = btf_get_by_fd(attr->value_type_btf_obj_fd);
>>>> +        if (IS_ERR(btf))
>>>> +            return ERR_PTR(PTR_ERR(btf));
>>>
>>>              return ERR_CAST(btf);
>>>
>>> It needs to check for btf_is_module:
>>>
>>>          if (!btf_is_module(btf)) {
>>>              btf_put(btf);
>>>              return ERR_PTR(-EINVAL);
>>>          }
>>
>> Even btf is btf_vmlinux the kernel's btf, it still works.
> 
> btf could be a bpf program's btf. It needs to ensure it is a kernel 
> module btf here.

Got it!

> 
>> Although libbpf pass 0 as the value of value_type_btf_obj_fd for
>> btf_vmlinux now, it should be OK for a user space loader to
>> pass a fd of btf_vmlinux.
>>
>> WDYT?
>