Re: [PATCH bpf-next 1/3] bpf: Check unsupported ops from the bpf_struct_ops's cfi_stubs

[Martin KaFai Lau <martin.lau@linux.dev>]

On 7/21/24 3:45 PM, Amery Hung wrote:
> On Sat, Jul 20, 2024 at 7:45 AM kernel test robot <lkp@intel.com> wrote:
>>
>> Hi Martin,
>>
>> kernel test robot noticed the following build warnings:
>>
>> [auto build test WARNING on bpf-next/master]
>>
>> url:    https://github.com/intel-lab-lkp/linux/commits/Martin-KaFai-Lau/bpf-Check-unsupported-ops-from-the-bpf_struct_ops-s-cfi_stubs/20240720-144313
>> base:   https://git.kernel.org/pub/scm/linux/kernel/git/bpf/bpf-next.git master
>> patch link:    https://lore.kernel.org/r/20240720062233.2319723-2-martin.lau%40linux.dev
>> patch subject: [PATCH bpf-next 1/3] bpf: Check unsupported ops from the bpf_struct_ops's cfi_stubs
>> config: i386-randconfig-001-20240720 (https://download.01.org/0day-ci/archive/20240720/202407202244.HvnUVyjM-lkp@intel.com/config)
>> compiler: gcc-7 (Ubuntu 7.5.0-6ubuntu2) 7.5.0
>> reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20240720/202407202244.HvnUVyjM-lkp@intel.com/reproduce)
>>
>> If you fix the issue in a separate patch/commit (i.e. not just a new version of
>> the same patch/commit), kindly add following tags
>> | Reported-by: kernel test robot <lkp@intel.com>
>> | Closes: https://lore.kernel.org/oe-kbuild-all/202407202244.HvnUVyjM-lkp@intel.com/
>>
>> All warnings (new ones prefixed by >>):
>>
>>     kernel/bpf/bpf_struct_ops.c: In function 'bpf_struct_ops_supported':
>>>> kernel/bpf/bpf_struct_ops.c:1045:48: warning: dereferencing 'void *' pointer
>>       void *func_ptr = *(void **)(&st_ops->cfi_stubs[moff]);
>>                                                     ^
>>
>>
>> vim +1045 kernel/bpf/bpf_struct_ops.c
>>
>>    1042
>>    1043  int bpf_struct_ops_supported(const struct bpf_struct_ops *st_ops, u32 moff)
>>    1044  {
>>> 1045          void *func_ptr = *(void **)(&st_ops->cfi_stubs[moff]);
> 
> The compiler warning can be fixed with:
> void *func_ptr = *(void **)(st_ops->cfi_stubs + moff);
> 
> The patch looks good to me. I tested it with bpf qdisc, and it does
> what it is supposed to do by prohibiting users to attach to an
> operator whose cfi stub is not defined.

Thanks for testing. I just tried gcc and can repro it. I will respin.