Re: [PATCH bpf-next] bpf: Check cfi_stubs before registering a struct_ops type.

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

On 2/15/24 11:19, Kui-Feng Lee wrote:
> 
> 
> On 2/15/24 10:23, Martin KaFai Lau wrote:
>> On 2/14/24 6:24 PM, thinker.li@gmail.com wrote:
>>> From: Kui-Feng Lee <thinker.li@gmail.com>
>>>
>>> Recently, cfi_stubs were introduced. However, existing struct_ops types
>>> that are not in the upstream may not be aware of this, resulting in 
>>> kernel
>>> crashes. By rejecting struct_ops types that do not provide cfi_stubs 
>>> during
>>> registration, these crashes can be avoided.
>>>
>>> Signed-off-by: Kui-Feng Lee <thinker.li@gmail.com>
>>> ---
>>>   kernel/bpf/bpf_struct_ops.c | 5 +++++
>>>   1 file changed, 5 insertions(+)
>>>
>>> diff --git a/kernel/bpf/bpf_struct_ops.c b/kernel/bpf/bpf_struct_ops.c
>>> index 0d7be97a2411..e35958142dce 100644
>>> --- a/kernel/bpf/bpf_struct_ops.c
>>> +++ b/kernel/bpf/bpf_struct_ops.c
>>> @@ -302,6 +302,11 @@ int bpf_struct_ops_desc_init(struct 
>>> bpf_struct_ops_desc *st_ops_desc,
>>>       }
>>>       sprintf(value_name, "%s%s", VALUE_PREFIX, st_ops->name);
>>> +    if (!st_ops->cfi_stubs) {
>>
>> How about *(void **)(st_ops->cfi_stubs + moff) ? Does it need a NULL 
>> check?
> 
> This NULL check is necessary to prevent the crash but good to have.
                     ^^^ I mean "not necessary"
> 
>>
>> Please add a test.
> 
> Got it!
> 
>>
>>> +        pr_warn("The struct_ops %s has no cfi_stubs\n", st_ops->name);
>>> +        return -EINVAL;
>>> +    }
>>> +
>>>       type_id = btf_find_by_name_kind(btf, st_ops->name,
>>>                       BTF_KIND_STRUCT);
>>>       if (type_id < 0) {
>>