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

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Message-Id: <20150525.001932.849051101973512567.davem@davemloft.net>
Date:	Mon, 25 May 2015 00:19:32 -0400 (EDT)
From:	David Miller <davem@...emloft.net>
To:	ast@...mgrid.com
Cc:	daniel@...earbox.net, edumazet@...gle.com, netdev@...r.kernel.org
Subject: Re: [PATCH net] x86: bpf_jit: fix compilation of large bpf programs

From: Alexei Starovoitov <ast@...mgrid.com>
Date: Fri, 22 May 2015 15:42:55 -0700

> 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>

Applied and queued up for -stable, thanks.
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