netdev - Re: [PATCH net-next] x86: bpf_jit_comp: secure bpf jit against spraying attacks

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Date:	Mon, 20 May 2013 16:19:41 +0200
From:	Florian Westphal <fw@...len.de>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	"H. Peter Anvin" <hpa@...or.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next] x86: bpf_jit_comp: secure bpf jit against
 spraying attacks

Eric Dumazet <eric.dumazet@...il.com> wrote:
> From: Eric Dumazet <edumazet@...gle.com>
> 
> hpa bringed into my attention some security related issues
> with BPF JIT on x86.
> 
> This patch makes sure the bpf generated code is marked read only,
> as other kernel text sections.
> 
> It also splits the unused space (we vmalloc() and only use a fraction of
> the page) in two parts, so that the generated bpf code not starts at a
> known offset in the page, but a pseudo random one.
> 
> Refs:
> http://mainisusuallyafunction.blogspot.com/2012/11/attacking-hardened-linux-systems-with.html

What about emitting additional instructions at random locations in the
generated code itself?

Eg., after every instruction, have random chance to insert
'xor $0xcc,%al; xor $0xcc,%al', etc?
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