netdev - Re: [PATCH net] x86: bpf_jit: fix compilation of large bpf programs

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Date:	Sat, 23 May 2015 00:46:43 +0200
From:	Daniel Borkmann <daniel@...earbox.net>
To:	Alexei Starovoitov <ast@...mgrid.com>,
	"David S. Miller" <davem@...emloft.net>
CC:	Eric Dumazet <edumazet@...gle.com>, netdev@...r.kernel.org
Subject: Re: [PATCH net] x86: bpf_jit: fix compilation of large bpf programs

On 05/23/2015 12:42 AM, Alexei Starovoitov wrote:
> x86 has variable length encoding. x86 JIT compiler is trying
> to pick the shortest encoding for given bpf instruction.
> While doing so the jump targets are changing, so JIT is doing
> multiple passes over the program. Typical program needs 3 passes.
> Some very short programs converge with 2 passes. Large programs
> may need 4 or 5. But specially crafted bpf programs may hit the
> pass limit and if the program converges on the last iteration
> the JIT compiler will be producing an image full of 'int 3' insns.
> Fix this corner case by doing final iteration over bpf program.
>
> Fixes: 0a14842f5a3c ("net: filter: Just In Time compiler for x86-64")
> Reported-by: Daniel Borkmann <daniel@...earbox.net>
> Signed-off-by: Alexei Starovoitov <ast@...mgrid.com>

LGTM, thanks!

Tested-by: Daniel Borkmann <daniel@...earbox.net>
Acked-by: Daniel Borkmann <daniel@...earbox.net>
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