From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757893AbcG0R7W (ORCPT ); Wed, 27 Jul 2016 13:59:22 -0400 Received: from mx1.redhat.com ([209.132.183.28]:42312 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756884AbcG0R7V (ORCPT ); Wed, 27 Jul 2016 13:59:21 -0400 Date: Wed, 27 Jul 2016 12:59:18 -0500 From: Josh Poimboeuf To: "Rafael J. Wysocki" Cc: "Rafael J. Wysocki" , Ingo Molnar , Borislav Petkov , Pavel Machek , Linux PM list , Linux Kernel Mailing List , Thomas Gleixner , shuzzle@mailbox.org Subject: Re: Fwd: [Bug 150021] New: kernel panic: "kernel tried to execute NX-protected page" when resuming from hibernate to disk Message-ID: <20160727175918.5uvo4p54iuhuw7ss@treble> References: <16541580.dFLT14ScxF@vostro.rjw.lan> <1931457.H9nCOt9KIt@vostro.rjw.lan> <20160726215319.twz22r5kbkpsgzfg@treble> <4852923.iQFmCCTKQM@vostro.rjw.lan> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.6.0.1 (2016-04-01) X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.27]); Wed, 27 Jul 2016 17:59:20 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jul 27, 2016 at 01:08:21AM +0200, Rafael J. Wysocki wrote: > On Wed, Jul 27, 2016 at 12:42 AM, Rafael J. Wysocki wrote: > > On Tuesday, July 26, 2016 04:53:19 PM Josh Poimboeuf wrote: > >> On Tue, Jul 26, 2016 at 10:15:39PM +0200, Rafael J. Wysocki wrote: > >> > On Tuesday, July 26, 2016 09:39:05 AM Josh Poimboeuf wrote: > >> > > On Tue, Jul 26, 2016 at 01:32:28PM +0200, Rafael J. Wysocki wrote: > >> > > > Hi, > >> > > > > >> > > > The following commit: > >> > > > > >> > > > commit 13523309495cdbd57a0d344c0d5d574987af007f > >> > > > Author: Josh Poimboeuf > >> > > > Date: Thu Jan 21 16:49:21 2016 -0600 > >> > > > > >> > > > x86/asm/acpi: Create a stack frame in do_suspend_lowlevel() > >> > > > > >> > > > do_suspend_lowlevel() is a callable non-leaf function which doesn't > >> > > > honor CONFIG_FRAME_POINTER, which can result in bad stack traces. > >> > > > > >> > > > Create a stack frame for it when CONFIG_FRAME_POINTER is enabled. > >> > > > > >> > > > is reported to cause a resume-from-hibernation regression due to an attempt > >> > > > to execute an NX page (we've seen quite a bit of that recently). > >> > > > > >> > > > I'm asking the reporter to try 4.7, but if the problem is still there, we'll > >> > > > need to revert the above I'm afraid. > >> > > >> > So the bug is still there in 4.7 and it goes away after reverting the above > >> > commit. I guess I'll send a revert then. > >> > >> Hm, the code in wakeup_64.S seems quite magical, but I can't figure out > >> why this change causes a panic. Is it really causing the panic or is it > >> uncovering some other bug? > > > > It doesn't matter really. > > > > It surely interacts with something in a really odd way, but that only means > > that its impact goes far beyond what was expected when it was applied. Its > > changelog is inadequate as a result and so on. > > > >> Maybe we should hold off on reverting until we understand the issue. > > > > Which very well may take forever. > > > > And AFAICS this is a fix for a theoretical issue and it *reliably* triggers a > > very practical kernel panic for this particular reporter. I'd rather live > > with the theoretical issue unfixed to be honest. > > Well, actually, the best part is that do_suspend_lowlevel() is not > even called during hibernation or resume from it. It only is called > during suspend-to-RAM. > > Question now is how the change made by the commit in question can > affect hibernation which is an unrelated code path. We know for a > fact that it does affect it, but how? Hm... I have a theory, but I'm not sure about it. I noticed that x86_acpi_enter_sleep_state(), which is involved in suspend, overwrites several global variables (e.g, initial_code) which are used by the CPU boot code in head_64.S. But surprisingly, it doesn't restore those variables to their original values after it resumes. So if a suspend and resume were done before the hibernate, those variables would presumably have suspend-centric values, and the first time a CPU is brought up during the hibernation restore operation, it would jump to wakeup_long64() (the suspend resume function) instead of start_secondary (which is the normal CPU boot function). So, if true, that would explain why my patch triggers a bug: wakeup_long64() always[*] jumps to .Lresume_point, which my patch affected. Because of the FRAME_END, it would pop an extra value off the stack. So when restore_processor_state() returns, it would return to whatever random address is on the stack after the real RIP. Which is consistent with the oops from the bug. It had a bad instruction pointer, which looked like a stack address. But then again, maybe there's a hole in that theory, because how could hibernate after suspend/resume possibly even work today if the CPU boot goes to wakeup_long64() instead of start_secondary? So I could be missing something, or even completely off base. But the missing restore of those variables does seem like a pretty huge oversight. I wonder if the following patch would fix it? diff --git a/arch/x86/kernel/acpi/sleep.c b/arch/x86/kernel/acpi/sleep.c index adb3eaf..cd76fc5 100644 --- a/arch/x86/kernel/acpi/sleep.c +++ b/arch/x86/kernel/acpi/sleep.c @@ -45,6 +45,12 @@ acpi_status asmlinkage __visible x86_acpi_enter_sleep_state(u8 state) */ int x86_acpi_suspend_lowlevel(void) { +#ifdef CONFIG_64BIT + unsigned long prev_initial_code; +#ifdef CONFIG_SMP + unsigned long prev_stack_start, prev_gdt_address, prev_initial_gs; +#endif +#endif struct wakeup_header *header = (struct wakeup_header *) __va(real_mode_header->wakeup_header); @@ -99,13 +105,18 @@ int x86_acpi_suspend_lowlevel(void) saved_magic = 0x12345678; #else /* CONFIG_64BIT */ #ifdef CONFIG_SMP + prev_stack_start = stack_start; + prev_gdt_address = early_gdt_descr.address; + prev_initial_gs = initial_gs; + stack_start = (unsigned long)temp_stack + sizeof(temp_stack); early_gdt_descr.address = (unsigned long)get_cpu_gdt_table(smp_processor_id()); initial_gs = per_cpu_offset(smp_processor_id()); #endif + prev_initial_code = initial_code; initial_code = (unsigned long)wakeup_long64; - saved_magic = 0x123456789abcdef0L; + saved_magic = 0x123456789abcdef0L; #endif /* CONFIG_64BIT */ /* @@ -115,6 +126,16 @@ int x86_acpi_suspend_lowlevel(void) pause_graph_tracing(); do_suspend_lowlevel(); unpause_graph_tracing(); + +#ifdef CONFIG_64BIT + initial_code = prev_initial_code; +#ifdef CONFIG_SMP + initial_gs = prev_initial_gs; + early_gdt_descr.address = prev_gdt_address; + stack_start = prev_stack_start; +#endif +#endif + return 0; }