diff options
author | Eric Dumazet <edumazet@google.com> | 2014-01-15 14:50:07 (GMT) |
---|---|---|
committer | David S. Miller <davem@davemloft.net> | 2014-01-16 01:02:08 (GMT) |
commit | aee636c4809fa54848ff07a899b326eb1f9987a2 (patch) | |
tree | 8f0c327f82dd7d5056dc487064f05f3f804f2fea | |
parent | ba42fad0964a41f0830e80c1b6be49c1e6bfcc01 (diff) | |
download | linux-aee636c4809fa54848ff07a899b326eb1f9987a2.tar.xz |
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>
-rw-r--r-- | arch/arm/net/bpf_jit_32.c | 6 | ||||
-rw-r--r-- | arch/powerpc/net/bpf_jit_comp.c | 7 | ||||
-rw-r--r-- | arch/s390/net/bpf_jit_comp.c | 17 | ||||
-rw-r--r-- | arch/sparc/net/bpf_jit_comp.c | 17 | ||||
-rw-r--r-- | arch/x86/net/bpf_jit_comp.c | 14 | ||||
-rw-r--r-- | net/core/filter.c | 30 |
6 files changed, 45 insertions, 46 deletions
diff --git a/arch/arm/net/bpf_jit_32.c b/arch/arm/net/bpf_jit_32.c index 9ed155a..271b5e9 100644 --- a/arch/arm/net/bpf_jit_32.c +++ b/arch/arm/net/bpf_jit_32.c @@ -641,10 +641,10 @@ 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); 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; diff --git a/arch/s390/net/bpf_jit_comp.c b/arch/s390/net/bpf_jit_comp.c index 16871da..fc0fa77 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) */ 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); diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c index 26328e8..4ed75dd 100644 --- a/arch/x86/net/bpf_jit_comp.c +++ b/arch/x86/net/bpf_jit_comp.c @@ -359,15 +359,21 @@ void bpf_jit_compile(struct sk_filter *fp) 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; diff --git a/net/core/filter.c b/net/core/filter.c index 01b7808..ad30d62 100644 --- a/net/core/filter.c +++ b/net/core/filter.c @@ -36,7 +36,6 @@ #include <asm/uaccess.h> #include <asm/unaligned.h> #include <linux/filter.h> -#include <linux/reciprocal_div.h> #include <linux/ratelimit.h> #include <linux/seccomp.h> #include <linux/if_vlan.h> @@ -166,7 +165,7 @@ unsigned int sk_run_filter(const struct sk_buff *skb, A /= X; continue; case BPF_S_ALU_DIV_K: - A = reciprocal_divide(A, K); + A /= K; continue; case BPF_S_ALU_MOD_X: if (X == 0) @@ -553,11 +552,6 @@ int sk_chk_filter(struct sock_filter *filter, unsigned int flen) /* Some instructions need special checks */ switch (code) { case BPF_S_ALU_DIV_K: - /* check for division by zero */ - if (ftest->k == 0) - return -EINVAL; - ftest->k = reciprocal_value(ftest->k); - break; case BPF_S_ALU_MOD_K: /* check for division by zero */ if (ftest->k == 0) @@ -853,27 +847,7 @@ void sk_decode_filter(struct sock_filter *filt, struct sock_filter *to) to->code = decodes[code]; to->jt = filt->jt; to->jf = filt->jf; - - if (code == BPF_S_ALU_DIV_K) { - /* - * When loaded this rule user gave us X, which was - * translated into R = r(X). Now we calculate the - * RR = r(R) and report it back. If next time this - * value is loaded and RRR = r(RR) is calculated - * then the R == RRR will be true. - * - * One exception. X == 1 translates into R == 0 and - * we can't calculate RR out of it with r(). - */ - - if (filt->k == 0) - to->k = 1; - else - to->k = reciprocal_value(filt->k); - - BUG_ON(reciprocal_value(to->k) != filt->k); - } else - to->k = filt->k; + to->k = filt->k; } int sk_get_filter(struct sock *sk, struct sock_filter __user *ubuf, unsigned int len) |