Re: [RFC bpf-next 2/4] bpf: return EOPNOTSUPP when map lookup isn't supported

[Prashant Bhole <bhole_prashant_q7@lab.ntt.co.jp>]

On 9/20/2018 12:14 AM, Alexei Starovoitov wrote:
> On Wed, Sep 19, 2018 at 04:51:41PM +0900, Prashant Bhole wrote:
>> Return ERR_PTR(-EOPNOTSUPP) from map_lookup_elem() methods of below
>> map types:
>> - BPF_MAP_TYPE_PROG_ARRAY
>> - BPF_MAP_TYPE_STACK_TRACE
>> - BPF_MAP_TYPE_XSKMAP
>> - BPF_MAP_TYPE_SOCKMAP/BPF_MAP_TYPE_SOCKHASH
>>
>> Signed-off-by: Prashant Bhole <bhole_prashant_q7@lab.ntt.co.jp>
>> ---
>>   kernel/bpf/arraymap.c | 2 +-
>>   kernel/bpf/sockmap.c  | 2 +-
>>   kernel/bpf/stackmap.c | 2 +-
>>   kernel/bpf/xskmap.c   | 2 +-
>>   4 files changed, 4 insertions(+), 4 deletions(-)
>>
>> diff --git a/kernel/bpf/arraymap.c b/kernel/bpf/arraymap.c
>> index dded84cbe814..24583da9ffd1 100644
>> --- a/kernel/bpf/arraymap.c
>> +++ b/kernel/bpf/arraymap.c
>> @@ -449,7 +449,7 @@ static void fd_array_map_free(struct bpf_map *map)
>>   
>>   static void *fd_array_map_lookup_elem(struct bpf_map *map, void *key)
>>   {
>> -	return NULL;
>> +	return ERR_PTR(-EOPNOTSUPP);
>>   }
> 
> conceptually the set looks good to me.
> Please add a test to test_verifier.c to make sure
> that these lookup helpers cannot be called from BPF program.
> Otherwise this diff may cause crashes.

Thanks for reviewing.
Is the verifier change below sufficient?

--- a/kernel/bpf/verifier.c
+++ b/kernel/bpf/verifier.c
@@ -2128,10 +2128,18 @@ static int check_map_func_compatibility(struct 
bpf_verifier_env *env,
  		if (env->subprog_cnt > 1) {
  			verbose(env, "tail_calls are not allowed in programs with 
bpf-to-bpf calls\n");
  			return -EINVAL;
  		}
  		break;
+	case BPF_FUNC_map_lookup_elem:
+		if (map->map_type == BPF_MAP_TYPE_PROG_ARRAY ||
+		    map->map_type == BPF_MAP_TYPE_STACK_TRACE ||
+		    map->map_type == BPF_MAP_TYPE_XSKMAP ||
+		    map->map_type == BPF_MAP_TYPE_SOCKMAP ||
+		    map->map_type == BPF_MAP_TYPE_SOCKHASH)
+			goto error;
+		break;
  	case BPF_FUNC_perf_event_read:
  	case BPF_FUNC_perf_event_output:
  	case BPF_FUNC_perf_event_read_value:
  		if (map->map_type != BPF_MAP_TYPE_PERF_EVENT_ARRAY)
  			goto error;

-Prashant