From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752349AbdLDQuz (ORCPT ); Mon, 4 Dec 2017 11:50:55 -0500 Received: from Galois.linutronix.de ([146.0.238.70]:59720 "EHLO Galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751852AbdLDQuu (ORCPT ); Mon, 4 Dec 2017 11:50:50 -0500 Message-Id: <20171204150604.991389777@linutronix.de> User-Agent: quilt/0.63-1 Date: Mon, 04 Dec 2017 15:07:08 +0100 From: Thomas Gleixner To: LKML Cc: x86@kernel.org, Linus Torvalds , Andy Lutomirsky , Peter Zijlstra , Dave Hansen , Borislav Petkov , Greg KH , keescook@google.com, hughd@google.com, Brian Gerst , Josh Poimboeuf , Denys Vlasenko , Rik van Riel , Boris Ostrovsky , Juergen Gross , David Laight , Eduardo Valentin , aliguori@amazon.com, Will Deacon , daniel.gruss@iaik.tugraz.at, Ingo Molnar Subject: [patch 02/60] x86/unwinder/orc: Dont bail on stack overflow References: <20171204140706.296109558@linutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=ISO-8859-15 Content-Disposition: inline; filename=x86-unwinder-orc--Dont_bail_on_stack_overflow.patch Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Andy Lutomirski If the stack overflows into a guard page and the ORC unwinder should work well: by construction, there can't be any meaningful data in the guard page because no writes to the guard page will have succeeded. But there is a bug that prevents unwinding from working correctly: if the starting register state has RSP pointing into a stack guard page, the ORC unwinder bails out immediately. Instead of bailing out immediately check whether the next page up is a valid check page and if so analyze that. As a result the ORC unwinder will start the unwind. Tested by intentionally overflowing the task stack. The result is an accurate call trace instead of a trace consisting purely of '?' entries. There are a few other bugs that are triggered if the unwinder encounters a stack overflow after the first step, but they are outside the scope of this fix. Signed-off-by: Andy Lutomirski Signed-off-by: Ingo Molnar Signed-off-by: Thomas Gleixner Cc: Peter Zijlstra Cc: Brian Gerst Cc: Dave Hansen Cc: Josh Poimboeuf Cc: Borislav Petkov Cc: Linus Torvalds Link: http://lkml.kernel.org/r/927042950d7f1a7007dd0f58538966a593508f8b.1511715954.git.luto@kernel.org --- arch/x86/kernel/unwind_orc.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) --- a/arch/x86/kernel/unwind_orc.c +++ b/arch/x86/kernel/unwind_orc.c @@ -553,8 +553,18 @@ void __unwind_start(struct unwind_state } if (get_stack_info((unsigned long *)state->sp, state->task, - &state->stack_info, &state->stack_mask)) - return; + &state->stack_info, &state->stack_mask)) { + /* + * We weren't on a valid stack. It's possible that + * we overflowed a valid stack into a guard page. + * See if the next page up is valid so that we can + * generate some kind of backtrace if this happens. + */ + void *next_page = (void *)PAGE_ALIGN((unsigned long)regs->sp); + if (get_stack_info(next_page, state->task, &state->stack_info, + &state->stack_mask)) + return; + } /* * The caller can provide the address of the first frame directly