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| author | Eric Dumazet <edumazet@google.com> | 2014-01-15 14:50:07 (GMT) |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2014-02-06 19:22:20 (GMT) |
| commit | a25dda5b26eed2d9246f9dfb9e7459c935a28557 (patch) | |
| tree | 4c69e44ece10e024a76c44c943d001f12202a206 /arch/sparc | |
| parent | 5e3b0f65e71dfa5c1a2e276f1a0df01a79aa07e3 (diff) | |
| download | linux-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/sparc')
| -rw-r--r-- | arch/sparc/net/bpf_jit_comp.c | 17 |
1 files changed, 14 insertions, 3 deletions
diff --git a/arch/sparc/net/bpf_jit_comp.c b/arch/sparc/net/bpf_jit_comp.c index 218b6b2..01fe994 100644 --- a/arch/sparc/net/bpf_jit_comp.c +++ b/arch/sparc/net/bpf_jit_comp.c @@ -497,9 +497,20 @@ void bpf_jit_compile(struct sk_filter *fp) case BPF_S_ALU_MUL_K: /* A *= K */ emit_alu_K(MUL, K); break; - case BPF_S_ALU_DIV_K: /* A /= K */ - emit_alu_K(MUL, K); - emit_read_y(r_A); + case BPF_S_ALU_DIV_K: /* A /= K with K != 0*/ + if (K == 1) + break; + emit_write_y(G0); +#ifdef CONFIG_SPARC32 + /* The Sparc v8 architecture requires + * three instructions between a %y + * register write and the first use. + */ + emit_nop(); + emit_nop(); + emit_nop(); +#endif + emit_alu_K(DIV, K); break; case BPF_S_ALU_DIV_X: /* A /= X; */ emit_cmpi(r_X, 0); |