From: "H. Peter Anvin" <hpa@linux.intel.com>
To: David Miller <davem@davemloft.net>, dborkman@redhat.com
Cc: ast@plumgrid.com, netdev@vger.kernel.org, hagen@jauu.net,
keescook@chromium.org, pmoore@redhat.com, mingo@kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH net-next v2 8/9] net: filter: rework/optimize internal BPF interpreter's instruction set
Date: Tue, 25 Mar 2014 17:24:27 -0700 [thread overview]
Message-ID: <53321E3B.8080709@linux.intel.com> (raw)
In-Reply-To: <20140325.201712.1651156258234145348.davem@davemloft.net>
On 03/25/2014 05:17 PM, David Miller wrote:
> From: Daniel Borkmann <dborkman@redhat.com>
> Date: Tue, 25 Mar 2014 13:10:56 +0100
>
>> - Conditional jt/jf targets replaced with jt/fall-through,
>> and forward/backward jumps now possible as well
>
> Ummm... does anyone even remember why backwards jumps were not allowed
> in the original BPF?
>
> It's to guarentee forward progress in the filter.
>
> Allowing branching backward would allow endless loops.
>
> Please remove this feature.
>
If you allow loops, it greatly increases the expressibility of the
language, but we would really need another control to limit CPU usage.
-hpa
next prev parent reply other threads:[~2014-03-26 0:24 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <1395749457-16178-1-git-send-email-dborkman@redhat.com>
2014-03-25 12:10 ` [PATCH net-next v2 8/9] net: filter: rework/optimize internal BPF interpreter's instruction set Daniel Borkmann
2014-03-26 0:17 ` David Miller
2014-03-26 0:24 ` H. Peter Anvin [this message]
2014-03-26 0:46 ` David Miller
2014-03-26 1:58 ` Alexei Starovoitov
2014-03-26 16:22 ` David Miller
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