From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752758AbdLAGa6 (ORCPT ); Fri, 1 Dec 2017 01:30:58 -0500 Received: from mail.kernel.org ([198.145.29.99]:43116 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752297AbdLAG3t (ORCPT ); Fri, 1 Dec 2017 01:29:49 -0500 DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 91967219A2 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=kernel.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=luto@kernel.org From: Andy Lutomirski To: x86@kernel.org Cc: linux-kernel@vger.kernel.org, Borislav Petkov , Brian Gerst , David Laight , Kees Cook , Peter Zijlstra , Andy Lutomirski Subject: [PATCH 1/6] x86/orc: Don't bail on stack overflow Date: Thu, 30 Nov 2017 22:29:41 -0800 Message-Id: <80f2f77dfb1b36e44d6870016b951aabbb48aaae.1512109321.git.luto@kernel.org> X-Mailer: git-send-email 2.13.6 In-Reply-To: References: In-Reply-To: References: Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org If we overflow the stack into a guard page and then try to unwind it with ORC, it 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. This patch fixes a bug that unwinding from working correctly: if the starting register state has RSP pointing into a stack guard page, the ORC unwinder bails out immediately. This patch fixes that: the ORC unwinder will start the unwind. I tested this 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, and Josh has WIP patches to fix those as well. Signed-off-by: Andy Lutomirski --- arch/x86/kernel/unwind_orc.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) diff --git a/arch/x86/kernel/unwind_orc.c b/arch/x86/kernel/unwind_orc.c index a3f973b2c97a..ff8e1132b2ae 100644 --- a/arch/x86/kernel/unwind_orc.c +++ b/arch/x86/kernel/unwind_orc.c @@ -553,8 +553,18 @@ void __unwind_start(struct unwind_state *state, struct task_struct *task, } 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)state->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 -- 2.13.6