On 06/17/2014 08:38 PM, Alexei Starovoitov wrote:
> On Tue, Jun 17, 2014 at 4:21 AM, Daniel Borkmann <dborkman@xxxxxxxxxx> wrote:
>> On 06/17/2014 01:09 PM, Markos Chandras wrote:
>> ...
>>>
>>> Thanks for these instructions. I will try them myself once I find some
>>>
>>> time since I don't think bpf_jit for MIPS has ever been tested with all
>>> the opcodes.
>>
>>
>> Sounds great! If you find some tests are missing, please feel free to
>> submit them as well via netdev.
>>
>> Best,
>>
>> Daniel
>
> Daniel,
>
> thank you for taking care of it so quickly :)
> from the BPF perspective the fix looks good:
> Acked-by: Alexei Starovoitov <ast@xxxxxxxxxxxx>
>
> Markos,
>
> please do run the testsuite.
> Doing quick code review of mips jit, it looks like:
>
> - your version of pkt_type_offset() will work for little endian only.
> (we've recently fixed it in net/core/filter.c)
>
> - vlan tag handling is incorrect, since it's missing shifts.
> classic BPF standard for vlan_tag_present has to return 1 or 0
> and not just emit_and(r_A, r_s0, VLAN_TAG_PRESENT, ctx);
>
> - pr_warn("%s: Unhandled opcode: 0x%02x\n", __FILE__,
> is way too heavy, since when jit is on, unprivileged user can spam log.
>
> - /* sa is 5-bits long */
> BUG_ON(sa >= BIT(5));
> is wrong too. Malicious user can cause kernel crash…
> Also shift A>>=33 was always allowed by classic BPF checker, so
> JITs have to silently do C-equivalent version of such shift.
>
> - /* Determine if immediate is within the 16-bit signed range */
> static inline bool is_range16(s32 imm)
> {
> if (imm >= SBIT(15) || imm < -SBIT(15))
> return true;
> the function name and comment are doing the opposite of
> actual code, which makes harder to follow.
>
> - the rest looks pretty good!
>
> Also you'll get a lot more mileage out of mips jit if you use eBPF
> instruction set as a base for JITing. You wouldn't need to worry
> about vlan, pkt_type and other classic extensions. You'll get all
> extensions for free, plus seccomp, tracing, etc.
>
> Thanks
> Alexei
>
Hi Alexei,
Thanks a lot for the feedback. I have already identified a few problems
which I have already fixed. I would like to move to eBPF but I can't
promise I can do it soon, so i think it's best to make sure that classic
BPF works fine for 3.16 and then I will make my plans for eBPF.
--
markos
