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

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Date:	Fri, 26 Sep 2014 15:03:31 -0700
From:	Alexei Starovoitov <ast@...mgrid.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	David Miller <davem@...emloft.net>, Ingo Molnar <mingo@...nel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Daniel Borkmann <dborkman@...hat.com>,
	Hannes Frederic Sowa <hannes@...essinduktion.org>,
	Chema Gonzalez <chema@...gle.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	Pablo Neira Ayuso <pablo@...filter.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Kees Cook <keescook@...omium.org>,
	Linux API <linux-api@...r.kernel.org>,
	Network Development <netdev@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: eBPF verifier thoughts (Re: [PATCH v15 net-next 00/11] eBPF
 syscall, verifier, testsuite)

On Fri, Sep 26, 2014 at 2:47 PM, Andy Lutomirski <luto@...capital.net> 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...

> 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?

> 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.
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