Re: Issues with bpf_trace_printk

[Daniel Borkmann <daniel@iogearbox.net>]

On 08/30/2017 11:50 PM, Zvi Effron wrote:
> I managed to set up my configuration with a VM on VMware Workstation,
> and it did not reproduce the bug. I think it was using one of the
> Intel drivers, though, instead of the generic. Is there a way to force
> the use of the generic driver?

I actually doubt that the trace printk issue you've seen has anything
to do with XDP native/generic side, but verifying it would be good
nevertheless.

For more recent iproute2, you can enforce either side (internally using
the XDP_FLAGS_DRV_MODE and XDP_FLAGS_SKB_MODE flags Dave just mentioned):

* Enforce native mode:

   ip link set dev foo xdpdrv obj ./xdp_test_kern.o sec .text

* Enforce generic mode:

   ip link set dev foo xdpgeneric obj ./xdp_test_kern.o sec .text

Did anything else change in your setup, like kernel config, etc, that
could play a role here?

Thanks,
Daniel

> On Wed, Aug 30, 2017 at 2:25 PM, Daniel Borkmann <daniel@iogearbox.net> wrote:
>> On 08/30/2017 07:53 PM, Zvi Effron wrote:
>>>
>>> I've uploaded the object file to
>>>
>>> https://drive.google.com/file/d/0B-lMs4mJOgQBU090ZzNtSkVnMTQ/view?usp=sharing
>>>
>>> uname -a output: Linux localhost.localdomain 4.12.8-300.fc26.x86_64 #1
>>> SMP Thu Aug 17 15:30:20 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux
>>>
>>> ip -V output: ip utility, iproute2-ss170501
>>>
>>> I tried with latest iproute2 built from source (ip -V output: ip
>>> utility, iproute2-ss170705) and am still having the same issue. (I
>>> also first noticed this with a custom loader I wrote, so I think the
>>> loader can probably be ruled out.)
>>>
>>> sysctl -a 2> /dev/null | grep bpf output:
>>> kernel.unprivileged_bpf_disabled = 0
>>> net.core.bpf_jit_enable = 0
>>> net.core.bpf_jit_harden = 0
>>> net.core.bpf_jit_kallsyms = 0
>>>
>>> Thanks for helping look into this! Let me know if you need any more info.
>>
>> Here are my results with your object file; seems to work fine
>> for me there, good but still strange. ;) I took the actual 4.12.8
>> stable kernel.
>>
>> # uname -a
>> Linux linux-2.home 4.12.8 #1 SMP Wed Aug 30 21:27:51 CEST 2017 x86_64 x86_64
>> x86_64 GNU/Linux
>> # ip -V
>> ip utility, iproute2-ss170705
>> # sysctl -a | grep bpf
>> kernel.unprivileged_bpf_disabled = 0
>> net.core.bpf_jit_enable = 0
>> net.core.bpf_jit_harden = 0
>> net.core.bpf_jit_kallsyms = 0
>> # ip link set dev wlp4s0 xdpgeneric obj ./xdp_test_kern.o sec .text
>> # tc exec bpf dbg                     # cmd is just finding mount and
>> dumping trace pipe
>> Running! Hang up with ^C!
>>
>>   irq/131-iwlwifi-710   [003] ....   892.116200: : Data start: 90941a    Data
>> end: 909456
>>   irq/131-iwlwifi-710   [003] ....   892.116216: : Constant: 1
>>   irq/131-iwlwifi-710   [003] ....   893.346855: : Data start: 90801a    Data
>> end: 908044
>>   irq/131-iwlwifi-710   [003] ....   893.346871: : Constant: 1
>>   irq/131-iwlwifi-710   [003] ....   893.346917: : Data start: 90801a    Data
>> end: 908070
>>   irq/131-iwlwifi-710   [003] ....   893.346921: : Constant: 1
>>   irq/131-iwlwifi-710   [003] ....   893.654076: : Data start: 90801a    Data
>> end: 908044
>>   irq/131-iwlwifi-710   [003] ....   893.654092: : Constant: 1
>>   irq/131-iwlwifi-710   [003] ....   901.333823: : Data start: 88dfc1a   Data
>> end: 88dfcb8
>>   irq/131-iwlwifi-710   [003] ....   901.333839: : Constant: 1
>>   irq/131-iwlwifi-710   [003] ....   907.578693: : Data start: 90801a    Data
>> end: 90804c
>>   irq/131-iwlwifi-710   [003] ....   907.578722: : Constant: 1
>>   irq/131-iwlwifi-710   [003] ....   908.192621: : Data start: 90801a    Data
>> end: 908044
>>   irq/131-iwlwifi-710   [003] ....   908.192634: : Constant: 1
>>   irq/131-iwlwifi-710   [003] ....   908.192696: : Data start: 90801a    Data
>> end: 908070
>>   irq/131-iwlwifi-710   [003] ....   908.192701: : Constant: 1
>>   irq/131-iwlwifi-710   [003] ....   908.920655: : Data start: 90801a    Data
>> end: 908044
>>   irq/131-iwlwifi-710   [003] ....   908.920661: : Constant: 1
>> [...]
>>
>> I attached the config I used just in case you want to try
>> building 4.12.8 kernel whether that changes anything. Would
>> be interesting to see.