Re: [RFC bpf-next 3/5] bpf: pin, translate, and unpin __kptr_user from syscalls.

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

On 8/12/24 10:36, Alexei Starovoitov wrote:
> On Mon, Aug 12, 2024 at 10:24 AM Kui-Feng Lee <sinquersw@gmail.com> wrote:
>>
>>
>>>> +static int bpf_map_update_value(struct bpf_map *map, struct file *map_file,
>>>> +                               void *key, void *value, __u64 flags)
>>>> +{
>>>> +       int err;
>>>> +
>>>> +       if (flags & BPF_FROM_USER) {
>>>
>>> there shouldn't be a need for this extra flag.
>>> map->record has the info whether uptr is present or not.
>>
>> The BPF_FROM_USER flag is used to support updating map values from BPF
>> programs as well. Although BPF programs can udpate map values, I
>> don't want the values of uptrs to be changed by the BPF programs.
>>
>> Should we just forbid the BPF programs to udpate the map values having
>> uptrs in them?
> 
> hmm. map_update_elem() is disallowed from bpf prog.
> 
>          case BPF_MAP_TYPE_TASK_STORAGE:
>                  if (func_id != BPF_FUNC_task_storage_get &&
>                      func_id != BPF_FUNC_task_storage_delete &&
>                      func_id != BPF_FUNC_kptr_xchg)
>                          goto error;

Thank you for the information!