x86: bpf_jit: fix compilation of large bpf programs
authorAlexei Starovoitov <ast@plumgrid.com>
Fri, 22 May 2015 22:42:55 +0000 (15:42 -0700)
committerDavid S. Miller <davem@davemloft.net>
Mon, 25 May 2015 04:18:35 +0000 (00:18 -0400)
commit3f7352bf21f8fd7ba3e2fcef9488756f188e12be
tree44c20470cf4a971a646330bfd5d55cfc985efe36
parentcc4a84c3da6f9dd6a297dc81fe4437643a60fe03
x86: bpf_jit: fix compilation of large bpf programs

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@iogearbox.net>
Signed-off-by: Alexei Starovoitov <ast@plumgrid.com>
Tested-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Daniel Borkmann <daniel@iogearbox.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
arch/x86/net/bpf_jit_comp.c