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

On Fri, Sep 26, 2014 at 3:03 PM, Alexei Starovoitov [off-list ref] wrote:

On Fri, Sep 26, 2014 at 2:47 PM, Andy Lutomirski [off-list ref] wrote:

quoted

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?

quoted

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.

quoted

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