From a25dda5b26eed2d9246f9dfb9e7459c935a28557 Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Wed, 15 Jan 2014 06:50:07 -0800 Subject: bpf: do not use reciprocal divide [ Upstream commit aee636c4809fa54848ff07a899b326eb1f9987a2 ] At first Jakub Zawadzki noticed that some divisions by reciprocal_divide were not correct. (off by one in some cases) http://www.wireshark.org/~darkjames/reciprocal-buggy.c He could also show this with BPF: http://www.wireshark.org/~darkjames/set-and-dump-filter-k-bug.c The reciprocal divide in linux kernel is not generic enough, lets remove its use in BPF, as it is not worth the pain with current cpus. Signed-off-by: Eric Dumazet Reported-by: Jakub Zawadzki Cc: Mircea Gherzan Cc: Daniel Borkmann Cc: Hannes Frederic Sowa Cc: Matt Evans Cc: Martin Schwidefsky Cc: Heiko Carstens Cc: David S. Miller Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- arch/powerpc/net/bpf_jit_comp.c | 7 ++++--- 1 file changed, 4 insertions(+), 3 deletions(-) (limited to 'arch/powerpc') diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c index 2345bdb4d91..ebbb2f1408f 100644 --- a/arch/powerpc/net/bpf_jit_comp.c +++ b/arch/powerpc/net/bpf_jit_comp.c @@ -209,10 +209,11 @@ static int bpf_jit_build_body(struct sk_filter *fp, u32 *image, } PPC_DIVWU(r_A, r_A, r_X); break; - case BPF_S_ALU_DIV_K: /* A = reciprocal_divide(A, K); */ + case BPF_S_ALU_DIV_K: /* A /= K */ + if (K == 1) + break; PPC_LI32(r_scratch1, K); - /* Top 32 bits of 64bit result -> A */ - PPC_MULHWU(r_A, r_A, r_scratch1); + PPC_DIVWU(r_A, r_A, r_scratch1); break; case BPF_S_ALU_AND_X: ctx->seen |= SEEN_XREG; -- cgit v1.2.3-18-g5258