netdev - Re: [RFC] bpf: remove global verifier state

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Date:   Wed, 4 Oct 2017 14:57:44 -0700
From:   Jakub Kicinski <kubakici@...pl>
To:     Daniel Borkmann <daniel@...earbox.net>
Cc:     Alexei Starovoitov <alexei.starovoitov@...il.com>,
        Eric Dumazet <eric.dumazet@...il.com>, dsahern@...il.com,
        netdev@...r.kernel.org, oss-drivers@...ronome.com,
        david.beckett@...ronome.com
Subject: Re: [RFC] bpf: remove global verifier state

On Wed, 04 Oct 2017 21:13:47 +0200, Daniel Borkmann wrote:
> On 10/04/2017 05:43 AM, Alexei Starovoitov wrote:
> > On Tue, Oct 03, 2017 at 08:24:06PM -0700, Eric Dumazet wrote:  
> >> On Tue, 2017-10-03 at 19:52 -0700, Alexei Starovoitov wrote:
> >>  
> >>> yep. looks great.
> >>> Please test it and submit officially :)
> >>> The commit aafe6ae9cee3 ("bpf: dynamically allocate digest scratch buffer")
> >>> fixed the other case where we were relying on the above mutex.
> >>> The only other spot to be adjusted is to add spin_lock/mutex or DO_ONCE() to
> >>> bpf_get_skb_set_tunnel_proto() to protect md_dst init.
> >>> imo that would be it.
> >>> Daniel, anything else comes to mind?  
> 
> Yes, this should be all. DO_ONCE() for the tunnel proto seems a
> good choice.

Hm.  I actually did:

if (!dst) {
	tmp = alloc();
	if (!tmp)
		return;
	if (cmpxchg(&dst, NULL, tmp))
		free(tmp);
}

I don't like how DO_ONCE() doesn't handle errors from the init
function :(

> >> 16 MB of log (unswappable kernel memory) per active checker.
> >>
> >> We might offer a way to oom hosts.  
> >
> > right. good point!
> > we need to switch to continuous copy_to_user() after a page or so.
> > Can even do it after every vscnprintf()
> > but page at a time is probably faster.  
> 
> Also worst case upper limits on verification side for holding state
> aside from the log would need to be checked in terms of how much mem
> we end up holding that is not accounted against any process (and not
> really "rate-limited" anymore once we drop the mutex).