Re: [PATCH] bpf: fix selftest/bpf/test_pkt_md_access on s390x

[Daniel Borkmann <daniel@iogearbox.net>]

On 08/04/2017 09:06 PM, Daniel Borkmann wrote:
> Hi Thomas,
>
> On 08/04/2017 08:40 AM, Thomas Richter wrote:
>> Commit 18f3d6be6be1 ("selftests/bpf: Add test cases to test narrower ctx field loads")
>> introduced new eBPF test cases. One of them (test_pkt_md_access.c)
>> fails on s390x. The BPF verifier error message is:
>
> Could you submit the fix to: netdev@vger.kernel.org
>
> (BPF patches are handled/accepted there.)
>
> Thanks a lot,
> Daniel
>
>> [root@s8360046 bpf]# ./test_progs
>> test_pkt_access:PASS:ipv4 349 nsec
>> test_pkt_access:PASS:ipv6 212 nsec
>> [....]
>> libbpf: load bpf program failed: Permission denied
>> libbpf: -- BEGIN DUMP LOG ---
>> libbpf:
>> 0: (71) r2 = *(u8 *)(r1 +0)
>> invalid bpf_context access off=0 size=1
>>
>> libbpf: -- END LOG --
>> libbpf: failed to load program 'test1'
>> libbpf: failed to load object './test_pkt_md_access.o'
>> Summary: 29 PASSED, 1 FAILED
>> [root@s8360046 bpf]#
>>
>> This is caused by a byte endianess issue. S390x is a big endian
>> architecture.  Pointer access to the lowest byte or halfword of a
>> four byte value need to add an offset.
>> On little endian architectures this offset is not needed.
>>
>> Fix this and use the same approach as the originator used for other files
>> (for example test_verifier.c) in his original commit.
>>
>> With this fix the test program test_progs succeeds on s390x:
>> [root@s8360046 bpf]# ./test_progs
>> test_pkt_access:PASS:ipv4 236 nsec
>> test_pkt_access:PASS:ipv6 217 nsec
>> test_xdp:PASS:ipv4 3624 nsec
>> test_xdp:PASS:ipv6 1722 nsec
>> test_l4lb:PASS:ipv4 926 nsec
>> test_l4lb:PASS:ipv6 1322 nsec
>> test_tcp_estats:PASS: 0 nsec
>> test_bpf_obj_id:PASS:get-fd-by-notexist-prog-id 0 nsec
>> test_bpf_obj_id:PASS:get-fd-by-notexist-map-id 0 nsec
>> test_bpf_obj_id:PASS:get-prog-info(fd) 0 nsec
>> test_bpf_obj_id:PASS:get-map-info(fd) 0 nsec
>> test_bpf_obj_id:PASS:get-prog-info(fd) 0 nsec
>> test_bpf_obj_id:PASS:get-map-info(fd) 0 nsec
>> test_bpf_obj_id:PASS:get-prog-fd(next_id) 0 nsec
>> test_bpf_obj_id:PASS:get-prog-info(next_id->fd) 0 nsec
>> test_bpf_obj_id:PASS:get-prog-fd(next_id) 0 nsec
>> test_bpf_obj_id:PASS:get-prog-info(next_id->fd) 0 nsec
>> test_bpf_obj_id:PASS:check total prog id found by get_next_id 0 nsec
>> test_bpf_obj_id:PASS:get-map-fd(next_id) 0 nsec
>> test_bpf_obj_id:PASS:get-map-fd(next_id) 0 nsec
>> test_bpf_obj_id:PASS:get-map-fd(next_id) 0 nsec
>> test_bpf_obj_id:PASS:get-map-fd(next_id) 0 nsec
>> test_bpf_obj_id:PASS:get-map-fd(next_id) 0 nsec
>> test_bpf_obj_id:PASS:get-map-fd(next_id) 0 nsec
>> test_bpf_obj_id:PASS:get-map-fd(next_id) 0 nsec
>> test_bpf_obj_id:PASS:check get-map-info(next_id->fd) 0 nsec
>> test_bpf_obj_id:PASS:get-map-fd(next_id) 0 nsec
>> test_bpf_obj_id:PASS:check get-map-info(next_id->fd) 0 nsec
>> test_bpf_obj_id:PASS:check total map id found by get_next_id 0 nsec
>> test_pkt_md_access:PASS: 277 nsec
>> Summary: 30 PASSED, 0 FAILED
>> [root@s8360046 bpf]#
>>
>> Signed-off-by: Thomas Richter <tmricht@linux.vnet.ibm.com>
>> ---
>>   tools/testing/selftests/bpf/test_pkt_md_access.c | 11 +++++++++++
>>   1 file changed, 11 insertions(+)
>>
>> diff --git a/tools/testing/selftests/bpf/test_pkt_md_access.c b/tools/testing/selftests/bpf/test_pkt_md_access.c
>> index 71729d4..8393ced 100644
>> --- a/tools/testing/selftests/bpf/test_pkt_md_access.c
>> +++ b/tools/testing/selftests/bpf/test_pkt_md_access.c
>> @@ -12,12 +12,23 @@
>>
>>   int _version SEC("version") = 1;
>>
>> +#ifdef __LITTLE_ENDIAN

One more thing I noticed, could you do above check with:

   #if __BYTE_ORDER__ == __ORDER_LITTLE_ENDIAN__

This is basically the version that clang exposes, so that
this could then properly be compiled with both, bpfel/bpfeb
targets, see also 78a5a93c1eeb ("bpf, tests: fix endianness
selection") for some more context.

Thanks again,
Daniel

>>   #define TEST_FIELD(TYPE, FIELD, MASK)                    \
>>       {                                \
>>           TYPE tmp = *(volatile TYPE *)&skb->FIELD;        \
>>           if (tmp != ((*(volatile __u32 *)&skb->FIELD) & MASK))    \
>>               return TC_ACT_SHOT;                \
>>       }
>> +#else
>> +#define TEST_FIELD_OFFSET(a, b)    ((sizeof(a) - sizeof(b)) / sizeof(b))
>> +#define TEST_FIELD(TYPE, FIELD, MASK)                    \
>> +    {                                \
>> +        TYPE tmp = *((volatile TYPE *)&skb->FIELD +        \
>> +                  TEST_FIELD_OFFSET(skb->FIELD, TYPE));    \
>> +        if (tmp != ((*(volatile __u32 *)&skb->FIELD) & MASK))    \
>> +            return TC_ACT_SHOT;                \
>> +    }
>> +#endif
>>
>>   SEC("test1")
>>   int process(struct __sk_buff *skb)