Le dimanche 18 mars 2012 à 19:35 +1100, Indan Zupancic a écrit : > And in the 00.00001% case that the filter uses a computed negative > offset the BPF JIT fails at runtime. So to not be buggy you need at > least a call to __load_pointer() for the negative case. Please show me how and why a real (I mean useful one...) filter could generate a dynamic negative value, and I'll change the code. Negative values are there to allow access to network/mac header components. I cant see how a BPF code could have a valid use of dynamic indexes in these headers. Right now we consider such code is evil and filter does "return 0" saying so. If I remember well, a more practical issue was mentioned by Matt Evans and I forgot about it. Its even _documented_ in his code. Thanks [PATCH] net: bpf_jit: fix BPF_S_LDX_B_MSH compilation Matt Evans spotted that x86 bpf_jit was incorrectly handling negative constant offsets in BPF_S_LDX_B_MSH instruction. We need to abort JIT compilation like we do in common_load so that filter uses the interpreter code and can call __load_pointer() Reference: http://lists.openwall.net/netdev/2011/07/19/11 Thanks to Indan Zupancic to bring back this issue. Reported-by: Matt Evans <matt@xxxxxxxxxx> Reported-by: Indan Zupancic <indan@xxxxxx> Signed-off-by: Eric Dumazet <eric.dumazet@xxxxxxxxx> --- David, libpcap doesnt generate such pattern, so feel to add this patch to net-next. Thanks ! arch/x86/net/bpf_jit_comp.c | 14 +++++--------- 1 file changed, 5 insertions(+), 9 deletions(-) diff --git a/arch/x86/net/bpf_jit_comp.c b/arch/x86/net/bpf_jit_comp.c index 7c1b765..5671752 100644 --- a/arch/x86/net/bpf_jit_comp.c +++ b/arch/x86/net/bpf_jit_comp.c @@ -475,8 +475,10 @@ void bpf_jit_compile(struct sk_filter *fp) case BPF_S_LD_W_ABS: func = sk_load_word; common_load: seen |= SEEN_DATAREF; - if ((int)K < 0) + if ((int)K < 0) { + /* Abort the JIT because __load_pointer() is needed. */ goto out; + } t_offset = func - (image + addrs[i]); EMIT1_off32(0xbe, K); /* mov imm32,%esi */ EMIT1_off32(0xe8, t_offset); /* call */ @@ -489,14 +491,8 @@ common_load: seen |= SEEN_DATAREF; goto common_load; case BPF_S_LDX_B_MSH: if ((int)K < 0) { - if (pc_ret0 > 0) { - /* addrs[pc_ret0 - 1] is the start address */ - EMIT_JMP(addrs[pc_ret0 - 1] - addrs[i]); - break; - } - CLEAR_A(); - EMIT_JMP(cleanup_addr - addrs[i]); - break; + /* Abort the JIT because __load_pointer() is needed. */ + goto out; } seen |= SEEN_DATAREF | SEEN_XREG; t_offset = sk_load_byte_msh - (image + addrs[i]); -- To unsubscribe from this list: send the line "unsubscribe linux-doc" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
