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>
diff --git a/arch/arm/net/bpf_jit_32.c b/arch/arm/net/bpf_jit_32.c
index 1a643ee..6de423d 100644
--- a/arch/arm/net/bpf_jit_32.c
+++ b/arch/arm/net/bpf_jit_32.c
@@ -637,10 +637,10 @@
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);
diff --git a/arch/powerpc/net/bpf_jit_comp.c b/arch/powerpc/net/bpf_jit_comp.c
index c427ae3..a012a97 100644
--- a/arch/powerpc/net/bpf_jit_comp.c
+++ b/arch/powerpc/net/bpf_jit_comp.c
@@ -209,10 +209,11 @@
}
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;
diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c
index 82f165f..b7792d4 100644
--- a/arch/s390/net/bpf_jit_comp.c
+++ b/arch/s390/net/bpf_jit_comp.c
@@ -338,11 +338,13 @@
/* 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;
@@ -358,6 +360,11 @@
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) */
diff --git a/arch/sparc/net/bpf_jit_comp.c b/arch/sparc/net/bpf_jit_comp.c
index d36a85e..fd95862 100644
--- a/arch/sparc/net/bpf_jit_comp.c
+++ b/arch/sparc/net/bpf_jit_comp.c
@@ -497,9 +497,20 @@
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);
diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c
index f66b540..0c966fe 100644
--- a/arch/x86/net/bpf_jit_comp.c
+++ b/arch/x86/net/bpf_jit_comp.c
@@ -324,15 +324,21 @@
EMIT2(0x89, 0xd0); /* mov %edx,%eax */
break;
case BPF_S_ALU_MOD_K: /* A %= K; */
+ if (K == 1) {
+ CLEAR_A();
+ break;
+ }
EMIT2(0x31, 0xd2); /* xor %edx,%edx */
EMIT1(0xb9);EMIT(K, 4); /* mov imm32,%ecx */
EMIT2(0xf7, 0xf1); /* div %ecx */
EMIT2(0x89, 0xd0); /* mov %edx,%eax */
break;
- case BPF_S_ALU_DIV_K: /* A = reciprocal_divide(A, K); */
- EMIT3(0x48, 0x69, 0xc0); /* imul imm32,%rax,%rax */
- EMIT(K, 4);
- EMIT4(0x48, 0xc1, 0xe8, 0x20); /* shr $0x20,%rax */
+ case BPF_S_ALU_DIV_K: /* A /= K */
+ if (K == 1)
+ break;
+ EMIT2(0x31, 0xd2); /* xor %edx,%edx */
+ EMIT1(0xb9);EMIT(K, 4); /* mov imm32,%ecx */
+ EMIT2(0xf7, 0xf1); /* div %ecx */
break;
case BPF_S_ALU_AND_X:
seen |= SEEN_XREG;