Re: eBPF verifier thoughts (Re: [PATCH v15 net-next 00/11] eBPF syscall, verifier, testsuite)

[Andy Lutomirski]

On Fri, Sep 26, 2014 at 3:03 PM, Alexei Starovoitov <ast@xxxxxxxxxxxx> wrote:
> On Fri, Sep 26, 2014 at 2:47 PM, Andy Lutomirski <luto@xxxxxxxxxxxxxx> wrote:
>>
>> Can't you just disallow the 1-byte write to the stack?
>
> of course not.
> That would be extremely limiting to users.
> Can you actually see yourself living with stack that only
> allows 8-byte writes/reads?
> The stack usage will increase a lot, since all char/short
> stack variables will become 8-byte...

How about requiring that sub-8-byte stack accesses only be to integer slots?

>
>> I'll try it in Python.  I bet I can get it to be shorter than the current code.
>
> Awesome challenge! :)
> I'll buy you a drink of your choice if you can achieve that.
> Also I'll send you our C programs that we use for
> testing to make sure, your python verifier can analyze them.
> If it passes, I'll be glad to rip mine out. Seriously.
> Deal?

Sure.

>
>> Yes, but does it work reliably?
>
> I'm not saying current verifier is perfect. It can get better.
> So far it was enough to let people code freely on top of it.



-- 
Andy Lutomirski
AMA Capital Management, LLC
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