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 21:55, Kui-Feng Lee wrote:
> 
> 
> 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!

Isn't btf_is_kernel() better here?
User space may pass a fd to btf_vmlinux.

> 
>>
>>> 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?
>>