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authorEric Dumazet <edumazet@google.com>2014-01-15 14:50:07 (GMT)
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2014-02-06 19:22:20 (GMT)
commita25dda5b26eed2d9246f9dfb9e7459c935a28557 (patch)
tree4c69e44ece10e024a76c44c943d001f12202a206 /arch/arm/net/bpf_jit_32.c
parent5e3b0f65e71dfa5c1a2e276f1a0df01a79aa07e3 (diff)
downloadlinux-fsl-qoriq-a25dda5b26eed2d9246f9dfb9e7459c935a28557.tar.xz
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 <edumazet@google.com> Reported-by: Jakub Zawadzki <darkjames-ws@darkjames.pl> Cc: Mircea Gherzan <mgherzan@gmail.com> Cc: Daniel Borkmann <dxchgb@gmail.com> Cc: Hannes Frederic Sowa <hannes@stressinduktion.org> Cc: Matt Evans <matt@ozlabs.org> Cc: Martin Schwidefsky <schwidefsky@de.ibm.com> Cc: Heiko Carstens <heiko.carstens@de.ibm.com> Cc: David S. Miller <davem@davemloft.net> Signed-off-by: David S. Miller <davem@davemloft.net> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'arch/arm/net/bpf_jit_32.c')
-rw-r--r--arch/arm/net/bpf_jit_32.c6
1 files changed, 3 insertions, 3 deletions
diff --git a/arch/arm/net/bpf_jit_32.c b/arch/arm/net/bpf_jit_32.c
index 99b44e0..8c9106f 100644
--- a/arch/arm/net/bpf_jit_32.c
+++ b/arch/arm/net/bpf_jit_32.c
@@ -637,10 +637,10 @@ load_ind:
emit(ARM_MUL(r_A, r_A, r_X), ctx);
break;
case BPF_S_ALU_DIV_K:
- /* current k == reciprocal_value(userspace k) */
+ if (k == 1)
+ break;
emit_mov_i(r_scratch, k, ctx);
- /* A = top 32 bits of the product */
- emit(ARM_UMULL(r_scratch, r_A, r_A, r_scratch), ctx);
+ emit_udiv(r_A, r_A, r_scratch, ctx);
break;
case BPF_S_ALU_DIV_X:
update_on_xread(ctx);