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authorEric Dumazet <edumazet@google.com>2014-01-15 14:50:07 (GMT)
committerDavid S. Miller <davem@davemloft.net>2014-01-16 01:02:08 (GMT)
commitaee636c4809fa54848ff07a899b326eb1f9987a2 (patch)
tree8f0c327f82dd7d5056dc487064f05f3f804f2fea /arch/powerpc
parentba42fad0964a41f0830e80c1b6be49c1e6bfcc01 (diff)
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')
-rw-r--r--arch/powerpc/net/bpf_jit_comp.c7
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 ac3c2a1..555034f 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;

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