From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751645AbdDMXCq (ORCPT ); Thu, 13 Apr 2017 19:02:46 -0400 Received: from smtprelay0061.hostedemail.com ([216.40.44.61]:60495 "EHLO smtprelay.hostedemail.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1751657AbdDMXCo (ORCPT ); Thu, 13 Apr 2017 19:02:44 -0400 X-Session-Marker: 726F737465647440676F6F646D69732E6F7267 X-Spam-Summary: 2,0,0,,d41d8cd98f00b204,rostedt@goodmis.org,:::::::::::::::::,RULES_HIT:41:355:379:541:599:800:960:973:988:989:1260:1277:1311:1313:1314:1345:1359:1437:1515:1516:1518:1534:1543:1593:1594:1711:1730:1747:1777:1792:2393:2553:2559:2562:2693:2896:2901:2903:3138:3139:3140:3141:3142:3355:3622:3865:3866:3867:3868:3870:3871:3872:3873:3874:4250:4605:5007:6261:7875:8660:10004:10400:10848:10967:11026:11232:11658:11914:12043:12296:12438:12555:12740:12760:12895:13148:13230:13255:13439:13618:13846:14096:14097:14181:14659:14721:21080:21433:21451:30003:30012:30054:30070:30090:30091,0,RBL:none,CacheIP:none,Bayesian:0.5,0.5,0.5,Netcheck:none,DomainCache:0,MSF:not bulk,SPF:,MSBL:0,DNSBL:none,Custom_rules:0:0:0,LFtime:2,LUA_SUMMARY:none X-HE-Tag: hands35_5144522e76924 X-Filterd-Recvd-Size: 4118 Date: Thu, 13 Apr 2017 19:02:36 -0400 From: Steven Rostedt To: Josh Poimboeuf Cc: Ingo Molnar , linux-kernel@vger.kernel.org, x86@kernel.org, Len Brown , linux-acpi@vger.kernel.org, Borislav Petkov , "Rafael J . Wysocki" , stable@kernel.org Subject: Re: [PATCH v3] ftrace/x86/32: fix triple fault with graph tracing and suspend-to-ram Message-ID: <20170413190236.7a225767@grimm.local.home> In-Reply-To: <5c1272269a580660703ed2eccf44308e790c7a98.1492123841.git.jpoimboe@redhat.com> References: <5c1272269a580660703ed2eccf44308e790c7a98.1492123841.git.jpoimboe@redhat.com> X-Mailer: Claws Mail 3.14.1 (GTK+ 2.24.31; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, 13 Apr 2017 17:53:55 -0500 Josh Poimboeuf wrote: > On x86-32, with CONFIG_FIRMWARE and multiple CPUs, if you enable > function graph tracing and then suspend to RAM, it will triple fault and > reboot when it resumes. > > The first fault happens when booting a secondary CPU: > > startup_32_smp() > load_ucode_ap() > prepare_ftrace_return() > ftrace_graph_is_dead() > (accesses 'kill_ftrace_graph') > > The early head_32.S code calls into load_ucode_ap(), which has an an > ftrace hook, so it calls prepare_ftrace_return(), which calls > ftrace_graph_is_dead(), which tries to access the global > 'kill_ftrace_graph' variable with a virtual address, causing a fault > because the CPU is still in real mode. > > The fix is to add a check in prepare_ftrace_return() to make sure it's > running in protected mode before continuing. The check makes sure the > stack pointer is a virtual kernel address. It's a bit of a hack, but > it's not very intrusive and it works well enough. > > For reference, here are a few other (more difficult) ways this could > have potentially been fixed: > > - Move startup_32_smp()'s call to load_ucode_ap() down to *after* paging > is enabled. (No idea what that would break.) > > - Track down load_ucode_ap()'s entire callee tree and mark all the > functions 'notrace'. (Probably not realistic.) > > - Pause graph tracing in ftrace_suspend_notifier_call() or bringup_cpu() > or __cpu_up(), and ensure that the pause facility can be queried from > real mode. > > Reported-by: Paul Menzel > Tested-by: Paul Menzel > Cc: stable@kernel.org > Signed-off-by: Josh Poimboeuf This is pretty much the same thing we were talking about before, right? If so, then: Reviewed-by: Steven Rostedt (VMware) if not, I need to spend more time reviewing it ;-) -- Steve > --- > v3: Added Tested-by: and Cc:stable tags > > arch/x86/kernel/ftrace.c | 12 ++++++++++++ > 1 file changed, 12 insertions(+) > > diff --git a/arch/x86/kernel/ftrace.c b/arch/x86/kernel/ftrace.c > index 9dd546b..a3adf1f 100644 > --- a/arch/x86/kernel/ftrace.c > +++ b/arch/x86/kernel/ftrace.c > @@ -995,6 +995,18 @@ void prepare_ftrace_return(unsigned long self_addr, unsigned long *parent, > unsigned long return_hooker = (unsigned long) > &return_to_handler; > > + /* > + * When resuming from suspend-to-ram, this function can be indirectly > + * called from early CPU startup code while the CPU is in real mode, > + * which would fail miserably. Make sure the stack pointer is a > + * virtual address. > + * > + * This check isn't as accurate as virt_addr_valid(), but it should be > + * good enough for this purpose, and it's fast. > + */ > + if (unlikely((long)__builtin_frame_address(0) >= 0)) > + return; > + > if (unlikely(ftrace_graph_is_dead())) > return; >