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| author | Eric Dumazet <edumazet@google.com> | 2014-01-15 06:50:07 -0800 |
|---|---|---|
| committer | David S. Miller <davem@davemloft.net> | 2014-01-15 17:02:08 -0800 |
| commit | aee636c4809fa54848ff07a899b326eb1f9987a2 (patch) | |
| tree | 8f0c327f82dd7d5056dc487064f05f3f804f2fea /arch/powerpc/net/bpf_jit_comp.c | |
| parent | ba42fad0964a41f0830e80c1b6be49c1e6bfcc01 (diff) | |
| download | blackbird-op-linux-aee636c4809fa54848ff07a899b326eb1f9987a2.tar.gz blackbird-op-linux-aee636c4809fa54848ff07a899b326eb1f9987a2.zip | |
bpf: do not use reciprocal divide
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>
Diffstat (limited to 'arch/powerpc/net/bpf_jit_comp.c')
| -rw-r--r-- | arch/powerpc/net/bpf_jit_comp.c | 7 |
1 files changed, 4 insertions, 3 deletions
diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c index ac3c2a10dafd..555034f8505e 100644 --- a/arch/powerpc/net/bpf_jit_comp.c +++ b/arch/powerpc/net/bpf_jit_comp.c @@ -223,10 +223,11 @@ 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; |
