Re: [PATCH RFC v2 net-next 10/16] bpf: add eBPF verifier

[Andy Lutomirski]

On Tue, Aug 12, 2014 at 1:00 PM, Alexei Starovoitov <ast@xxxxxxxxxxxx> wrote:
> On Tue, Aug 12, 2014 at 12:32 PM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
>> On Thu, Jul 24, 2014 at 12:25 PM, Alexei Starovoitov <ast@xxxxxxxxxxxx> wrote:
>>> On Thu, Jul 24, 2014 at 11:25 AM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
>>>> On Thu, Jul 17, 2014 at 9:20 PM, Alexei Starovoitov <ast@xxxxxxxxxxxx> wrote:
>>>>> Safety of eBPF programs is statically determined by the verifier, which detects:
>>>>> - loops
>>>>> - out of range jumps
>>>>> - unreachable instructions
>>>>> - invalid instructions
>>>>> - uninitialized register access
>>>>> - uninitialized stack access
>>>>> - misaligned stack access
>>>>> - out of range stack access
>>>>> - invalid calling convention
>>>>
>>>> Is there something that documents exactly what conditions an eBPF
>>>> program must satisfy in order to be considered valid?
>>>
>>> I did a writeup in the past on things that verifiers checks and gave it
>>> to internal folks to review. Guys have said that now they understand very
>>> well how it works, but in reality it didn't help at all to write valid programs.
>>> What worked is 'verification trace' = the instruction by instruction dump
>>> of verifier state while it's analyzing the program.
>>> I gave few simple examples of it in
>>> 'Understanding eBPF verifier messages' section:
>>> https://git.kernel.org/cgit/linux/kernel/git/ast/bpf.git/diff/Documentation/networking/filter.txt?id=b22459133b9f52d2176c8c0f8b5eb036478a40c9
>>> Every example there is what "program must satisfy to be valid"...
>>>
>>> Therefore I'm addressing two things:
>>> 1. how verifier works and what it checks for.
>>>   that is described in 'eBPF verifier' section of the doc and
>>>   in 200 lines of comments inside verifier.c
>>
>> That doc is pretty good.  I'll try to read it carefully soon.  Sorry
>> for the huge delay here -- I've been on vacation.
>
> I've been sitting on v4 for few weeks, since it's a merge window.
> So please hold on a careful review. I'll post v4 later today.
> Mainly I've split the verifier into several patches to make it
> easier to read.
> Thanks!

Will you be at KS / LSS / LinuxCon?

--Andy

-- 
Andy Lutomirski
AMA Capital Management, LLC
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