Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752814AbaBXRIv (ORCPT ); Mon, 24 Feb 2014 12:08:51 -0500 Received: from mail-qa0-f43.google.com ([209.85.216.43]:43522 "EHLO mail-qa0-f43.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752253AbaBXRIu (ORCPT ); Mon, 24 Feb 2014 12:08:50 -0500 Date: Mon, 24 Feb 2014 12:10:44 -0500 (EST) From: Vince Weaver To: "H. Peter Anvin" cc: Vince Weaver , Linux Kernel , Peter Zijlstra , Ingo Molnar , "H.J. Lu" Subject: Re: perf_fuzzer compiled for x32 causes reboot In-Reply-To: <18f0cea3-7e3b-4477-b433-0269f3de976b@email.android.com> Message-ID: References: <53084317.4090304@zytor.com> <530AD71E.50800@zytor.com> <18f0cea3-7e3b-4477-b433-0269f3de976b@email.android.com> User-Agent: Alpine 2.10 (DEB 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 24 Feb 2014, H. Peter Anvin wrote: > On February 24, 2014 8:34:30 AM PST, Vince Weaver wrote: > >On Mon, 24 Feb 2014, Vince Weaver wrote: > > > >> Just touching the mmap page with a write of a single byte (it doesn't > > > >> matter where) is enough to trigger the bug. > > > >OK, investigating this more. > > > >perf_fuzzer-2971 [000] 154.944114: page_fault_user: > >address=0xf7729000 ip=0x41efab error_code=0x6 > >perf_fuzzer-2971 [000] 154.944118: function: > >ip=0xffffffff810d40e7 parent_ip=0xffffffff810d0840 > >perf_fuzzer-2971 [000] 154.944119: function: > >ip=0xffffffff812a91a5 parent_ip=0xffffffff81013ff5 > >perf_fuzzer-2971 [000] 154.944120: function: > >ip=0xffffffff8153837c parent_ip=0xffffffff81535432 > >perf_fuzzer-2971 [000] 154.944121: page_fault_kernel: > >address=0x22e0 ip=0xffffffff812a7d5c error_code=0x0 > Ok, so the obvious question is what is at that kernel address? > It's in copy_user_generic_string() rep movsq %ds:(%rsi),%es:(%rdi) And looking at the ftrace: perf_fuzzer-2979 [000] 161.475920: page_fault_user: address=__per_cpu_end ip=__per_cpu_end error_code=0x6 perf_fuzzer-2979 [000] 161.475922: function: perf_callchain perf_fuzzer-2979 [000] 161.475922: function: copy_from_user_nmi perf_fuzzer-2979 [000] 161.475923: function: trace_do_page_fault perf_fuzzer-2979 [000] 161.475924: page_fault_kernel: address=irq_stack_union ip=copy_user_generic_string error_code=0x0 What is likely happening is the user page fault is triggering code to do a "perf_callchain" dump, which is calling copy_from_user_nmi() which calls copy_user_generic_string() which is somehow getting the user RBP in the RDI register somehow? Vince -- 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/