From 3f7352bf21f8fd7ba3e2fcef9488756f188e12be Mon Sep 17 00:00:00 2001 From: Alexei Starovoitov Date: Fri, 22 May 2015 15:42:55 -0700 Subject: [PATCH] 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 Signed-off-by: Alexei Starovoitov Tested-by: Daniel Borkmann Acked-by: Daniel Borkmann Signed-off-by: David S. Miller --- arch/x86/net/bpf_jit_comp.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c index 99f76103c6b7..ddeff4844a10 100644 --- a/arch/x86/net/bpf_jit_comp.c +++ b/arch/x86/net/bpf_jit_comp.c @@ -966,7 +966,12 @@ void bpf_int_jit_compile(struct bpf_prog *prog) } ctx.cleanup_addr = proglen; - for (pass = 0; pass < 10; pass++) { + /* JITed image shrinks with every pass and the loop iterates + * until the image stops shrinking. Very large bpf programs + * may converge on the last pass. In such case do one more + * pass to emit the final image + */ + for (pass = 0; pass < 10 || image; pass++) { proglen = do_jit(prog, addrs, image, oldproglen, &ctx); if (proglen <= 0) { image = NULL; -- GitLab