arch: arm: bpf: Converting cBPF to eBPF for arm 32 bit

[Shubham Bansal]

Hi Daniel,

I just tried running test_bpf.ko module.

$ echo 2 >>  /proc/sys/net/core/bpf_jit_enable
$ insmod test_bpf.ko

test_bpf: #0 TAX
bpf_jit: flen=14 proglen=212 pass=2 image=7f15a83c from=insmod pid=730
JIT code: 00000000: f0 05 2d e9 40 d2 4d e2 00 40 a0 e3 0c 42 8d e5
JIT code: 00000010: 08 42 8d e5 00 00 20 e0 01 10 21 e0 20 62 9d e5
JIT code: 00000020: 20 72 9d e5 06 70 27 e0 20 72 8d e5 24 62 9d e5
JIT code: 00000030: 24 72 9d e5 06 70 27 e0 24 72 8d e5 00 40 a0 e1
JIT code: 00000040: 01 50 a0 e1 01 00 a0 e3 00 10 a0 e3 20 02 8d e5
JIT code: 00000050: 24 12 8d e5 02 00 a0 e3 00 10 a0 e3 20 62 9d e5
JIT code: 00000060: 06 00 80 e0 00 10 a0 e3 00 00 60 e2 00 10 a0 e3
JIT code: 00000070: 20 02 8d e5 24 12 8d e5 54 40 90 e5 20 62 9d e5
JIT code: 00000080: 06 00 80 e0 00 10 a0 e3 20 02 8d e5 24 12 8d e5
JIT code: 00000090: 04 00 a0 e1 01 10 a0 e3 20 62 9d e5 06 10 81 e0
JIT code: 000000a0: 01 20 a0 e3 04 32 8d e2 bc 68 0a e3 11 60 48 e3
JIT code: 000000b0: 36 ff 2f e1 01 10 21 e0 00 00 50 e3 04 00 00 0a
JIT code: 000000c0: 00 00 d0 e5 01 00 00 ea 40 d2 8d e2 f0 05 bd e8
JIT code: 000000d0: 1e ff 2f e1
jited:1
Unhandled fault: page domain fault (0x01b) at 0x00000051
pgd = 871d0000
[00000051] *pgd=671b7831, *pte=00000000, *ppte=00000000
Internal error: : 1b [#1] SMP ARM
Modules linked in: test_bpf(+)
CPU: 0 PID: 730 Comm: insmod Not tainted 4.11.0+ #5
Hardware name: ARM-Versatile Express
task: 87023700 task.stack: 8718a000
PC is at 0x7f15a8b4
LR is at test_bpf_init+0x5bc/0x1000 [test_bpf]
pc : [<7f15a8b4>]    lr : [<7f1575bc>]    psr: 80000013
sp : 8718bd7c  ip : 00000015  fp : 7f005008
r10: 7f005094  r9 : 893ba020  r8 : 893ba000
r7 : 00000000  r6 : 00000001  r5 : 00000000  r4 : 00000000
r3 : 7f15a83c  r2 : 893ba020  r1 : 00000000  r0 : fffffffd
Flags: Nzcv  IRQs on  FIQs on  Mode SVC_32  ISA ARM  Segment none
Control: 10c5387d  Table: 671d0059  DAC: 00000051
Process insmod (pid: 730, stack limit = 0x8718a210)
Stack: (0x8718bd7c to 0x8718c000)
bd60:                                                                00000000
bd80: 00002710 870db300 c302e7e8 7f004010 893ba000 7f005094 00000000 00000000
bda0: 00000000 00000000 00000000 00000001 00000001 00000000 014000c0 00150628
bdc0: 7f0050ac 7f154840 1234aaaa 1234aaab c302e7e8 0000000f 00000000 893ba000
bde0: 0000000b 7f004010 87fd54a0 ffffe000 7f157000 00000000 871b6fc0 00000001
be00: 78e4905c 00000024 7f154640 8010179c 80a06544 8718a000 00000001 80a54980
be20: 80a3066c 00000007 809685c0 80a54700 80a54700 07551000 80a54700 60070013
be40: 7f154640 801f3fc8 78e4905c 7f154640 00000001 871b6fe4 7f154640 00000001
be60: 871b6b00 00000001 78e4905c 801eaa94 00000001 871b6fe4 8718bf44 00000001
be80: 871b6fe4 80196e4c 7f15464c 00007fff 7f154640 80193f10 87127000 7f154640
bea0: 7f154688 80703800 7f154770 807037e4 8081b184 807bec60 807becc4 807bec6c
bec0: 7f15481c 8010c1b8 93600000 76ed8028 00000f60 00000000 00000000 00000000
bee0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
bf00: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00003f80
bf20: 76f5cf88 00000000 93684f80 8718a000 00160fda 00000051 00000000 801973b0
bf40: 87671a00 93501000 00183f80 93684760 93684574 936788e0 00155000 00155290
bf60: 00000000 00000000 00000000 00001f64 00000032 00000033 0000001d 00000000
bf80: 00000017 00000000 00000000 00183f80 756e694c 00000080 80107684 fffffffd
bfa0: 00000000 801074c0 00000000 00183f80 76dd9008 00183f80 00160fda 00000000
bfc0: 00000000 00183f80 756e694c 00000080 00000001 7eabae2c 00172f8c 00000000
bfe0: 7eabaae0 7eabaad0 0004017f 00013172 60070030 76dd9008 00000000 00000000
[<7f1575bc>] (test_bpf_init [test_bpf]) from [<7f157000>]
(test_bpf_init+0x0/0x1000 [test_bpf])
[<7f157000>] (test_bpf_init [test_bpf]) from [<78e4905c>] (0x78e4905c)
Code: e2600000 e3a01000 e58d0220 e58d1224 (e5904054)
---[ end trace a36398923b914fe2 ]---
Segmentation fault

Why is trying to execute TAX which is a cBPF instruction?

Best,
Shubham Bansal


On Thu, Apr 6, 2017 at 6:21 PM, Daniel Borkmann <daniel at iogearbox.net> wrote:
> On 04/06/2017 01:05 PM, Shubham Bansal wrote:
>>
>> Gentle Reminder.
>
>
> Sorry for late reply.
>
>> Anybody can tell me how to test the JIT compiler ?
>
>
> There's lib/test_bpf.c, see Documentation/networking/filter.txt +1349
> for some more information. It basically contains various test cases that
> have the purpose to test the JIT with corner cases. If you see a useful
> test missing, please send a patch for it, so all other JITs can benefit
> from this as well. For extracting disassembly from a generated test case,
> check out bpf_jit_disasm (Documentation/networking/filter.txt +486).
>
> Thanks,
> Daniel