Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755521Ab3DZPLi (ORCPT ); Fri, 26 Apr 2013 11:11:38 -0400 Received: from mail-pb0-f44.google.com ([209.85.160.44]:53922 "EHLO mail-pb0-f44.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750936Ab3DZPLh (ORCPT ); Fri, 26 Apr 2013 11:11:37 -0400 Message-ID: <1366989094.8964.212.camel@edumazet-glaptop> Subject: Re: [RFC PATCH net-next 2/6] x86: bpf_jit_comp: support BPF_S_ANC_SECCOMP_LD_W instruction From: Eric Dumazet To: Xi Wang Cc: Daniel Borkmann , "David S. Miller" , Russell King , Heiko Carstens , Eric Dumazet , Will Drewry , Andrew Morton , netdev@vger.kernel.org, linux-kernel@vger.kernel.org Date: Fri, 26 Apr 2013 08:11:34 -0700 In-Reply-To: References: <1366962706-24204-1-git-send-email-xi.wang@gmail.com> <1366962706-24204-3-git-send-email-xi.wang@gmail.com> <1366985926.8964.190.camel@edumazet-glaptop> Content-Type: text/plain; charset="UTF-8" X-Mailer: Evolution 3.2.3-0ubuntu6 Content-Transfer-Encoding: 7bit Mime-Version: 1.0 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1969 Lines: 54 On Fri, 2013-04-26 at 10:50 -0400, Xi Wang wrote: > On Fri, Apr 26, 2013 at 10:18 AM, Eric Dumazet wrote: > > On Fri, 2013-04-26 at 03:51 -0400, Xi Wang wrote: > > > >> +#ifdef CONFIG_SECCOMP_FILTER > >> + case BPF_S_ANC_SECCOMP_LD_W: > >> + if (K == offsetof(struct seccomp_data, arch)) { > >> + int arch = syscall_get_arch(current, NULL); > >> + > >> + EMIT1_off32(0xb8, arch); /* mov arch,%eax */ > >> + break; > >> + } > >> + func = (u8 *)seccomp_bpf_load; > >> + t_offset = func - (image + addrs[i]); > >> + EMIT1_off32(0xbf, K); /* mov imm32,%edi */ > >> + EMIT1_off32(0xe8, t_offset); /* call seccomp_bpf_load */ > >> + break; > >> +#endif > > > > This seems seriously wrong to me. > > Can you elaborate? > > > This cannot have been tested at all. > > Thanks to QEMU for hiding bugs then. :) 1) 'current' at the time the code is jitted (compiled) is not the 'current' at the time the filter will be evaluated. On x86_64, if CONFIG_IA32_EMULATION=y, syscall_get_arch() evaluates to : if (task_thread_info(task)->status & TS_COMPAT) return AUDIT_ARCH_I386; return AUDIT_ARCH_X86_64; So your code is completely wrong. 2) Calling a function potentially destroys some registers. %rdi,%r8,%r9 for instance, so we are going to crash very easily. I dont know, I feel a bit uncomfortable having to explain this to someone sending security related patches... -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/