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| author | Eric Dumazet <edumazet@google.com> | 2014-01-15 06:50:07 -0800 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2014-02-06 11:22:20 -0800 |
| commit | a25dda5b26eed2d9246f9dfb9e7459c935a28557 (patch) | |
| tree | 4c69e44ece10e024a76c44c943d001f12202a206 /arch/arm | |
| parent | 5e3b0f65e71dfa5c1a2e276f1a0df01a79aa07e3 (diff) | |
| download | linux-rt-a25dda5b26eed2d9246f9dfb9e7459c935a28557.tar.gz | |
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')
| -rw-r--r-- | arch/arm/net/bpf_jit_32.c | 6 |
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 99b44e0e8d86..8c9106fd8163 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); |