linux-kernel - Re: [PATCH v6 net-next 1/6] net: filter: add "load 64-bit immediate" eBPF instruction

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Message-Id: <20140825.180621.1003932711320755950.davem@davemloft.net>
Date:	Mon, 25 Aug 2014 18:06:21 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	ast@...mgrid.com
Cc:	mingo@...nel.org, torvalds@...ux-foundation.org,
	luto@...capital.net, rostedt@...dmis.org, dborkman@...hat.com,
	chema@...gle.com, edumazet@...gle.com, a.p.zijlstra@...llo.nl,
	brendan.d.gregg@...il.com, namhyung@...nel.org, hpa@...or.com,
	akpm@...ux-foundation.org, keescook@...omium.org,
	linux-api@...r.kernel.org, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 net-next 1/6] net: filter: add "load 64-bit
 immediate" eBPF instruction

From: Alexei Starovoitov <ast@...mgrid.com>
Date: Mon, 25 Aug 2014 18:00:53 -0700

> add BPF_LD_IMM64 instruction to load 64-bit immediate value into a register.

I think you need to rethink this.

I understand that you want to be able to compile arbitrary C code into
eBPF, but you have to restrict strongly what data the eBPF code can get
to.

Arbitrary pointer loads is asking for trouble.

Instead I would rather you look into a model like what the quake
engine uses for it's VM.

Namely, the program can do loads and stores from/to a data section,
but all of them are validated to be in the range of the VM program's
image.

eBPF programs should only be able to access things using either:

1) Well defined entry/exit points for control transfer

2) Load/Store within a private limited data segment range used
   only by the eBPF program

I don't want the eBPF program to be able to get "out of it's box"
in any way shape or form.

And besides, you're only making this thing as an optimization right?
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