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authorEric Dumazet <edumazet@google.com>2014-01-15 06:50:07 -0800
committerDavid S. Miller <davem@davemloft.net>2014-01-15 17:02:08 -0800
commitaee636c4809fa54848ff07a899b326eb1f9987a2 (patch)
tree8f0c327f82dd7d5056dc487064f05f3f804f2fea /arch/s390/net
parentba42fad0964a41f0830e80c1b6be49c1e6bfcc01 (diff)
downloadlinux-aee636c4809fa54848ff07a899b326eb1f9987a2.tar.gz
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/s390/net')
-rw-r--r--arch/s390/net/bpf_jit_comp.c17
1 files changed, 12 insertions, 5 deletions
diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c
index 16871da37371..fc0fa77728e1 100644
--- a/arch/s390/net/bpf_jit_comp.c
+++ b/arch/s390/net/bpf_jit_comp.c
@@ -371,11 +371,13 @@ static int bpf_jit_insn(struct bpf_jit *jit, struct sock_filter *filter,
/* dr %r4,%r12 */
EMIT2(0x1d4c);
break;
- case BPF_S_ALU_DIV_K: /* A = reciprocal_divide(A, K) */
- /* m %r4,<d(K)>(%r13) */
- EMIT4_DISP(0x5c40d000, EMIT_CONST(K));
- /* lr %r5,%r4 */
- EMIT2(0x1854);
+ case BPF_S_ALU_DIV_K: /* A /= K */
+ if (K == 1)
+ break;
+ /* lhi %r4,0 */
+ EMIT4(0xa7480000);
+ /* d %r4,<d(K)>(%r13) */
+ EMIT4_DISP(0x5d40d000, EMIT_CONST(K));
break;
case BPF_S_ALU_MOD_X: /* A %= X */
jit->seen |= SEEN_XREG | SEEN_RET0;
@@ -391,6 +393,11 @@ static int bpf_jit_insn(struct bpf_jit *jit, struct sock_filter *filter,
EMIT2(0x1854);
break;
case BPF_S_ALU_MOD_K: /* A %= K */
+ if (K == 1) {
+ /* lhi %r5,0 */
+ EMIT4(0xa7580000);
+ break;
+ }
/* lhi %r4,0 */
EMIT4(0xa7480000);
/* d %r4,<d(K)>(%r13) */