From mboxrd@z Thu Jan 1 00:00:00 1970 Received: with ECARTIS (v1.0.0; list linux-mips); Sun, 10 Sep 2017 00:26:26 +0200 (CEST) Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:38439 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by eddie.linux-mips.org with ESMTP id S23994827AbdIIWY40VTYB (ORCPT ); Sun, 10 Sep 2017 00:24:56 +0200 Received: from [2a02:8011:400e:2:6f00:88c8:c921:d332] (helo=deadeye) by shadbolt.decadent.org.uk with esmtps (TLS1.2:ECDHE_RSA_AES_256_GCM_SHA384:256) (Exim 4.84_2) (envelope-from ) id 1dqoBI-00014U-Hg; Sat, 09 Sep 2017 23:24:52 +0100 Received: from ben by deadeye with local (Exim 4.89) (envelope-from ) id 1dqoBG-0006zm-P2; Sat, 09 Sep 2017 23:24:50 +0100 Content-Type: text/plain; charset="UTF-8" Content-Disposition: inline Content-Transfer-Encoding: 8bit MIME-Version: 1.0 From: Ben Hutchings To: linux-kernel@vger.kernel.org, stable@vger.kernel.org CC: akpm@linux-foundation.org, linux-mips@linux-mips.org, "Ralf Baechle" , "James Hogan" Date: Sat, 09 Sep 2017 22:47:15 +0100 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.16 226/233] MIPS: Avoid accidental raw backtrace In-Reply-To: X-SA-Exim-Connect-IP: 2a02:8011:400e:2:6f00:88c8:c921:d332 X-SA-Exim-Mail-From: ben@decadent.org.uk X-SA-Exim-Scanned: No (on shadbolt.decadent.org.uk); SAEximRunCond expanded to false Return-Path: X-Envelope-To: <"|/home/ecartis/ecartis -s linux-mips"> (uid 0) X-Orcpt: rfc822;linux-mips@linux-mips.org Original-Recipient: rfc822;linux-mips@linux-mips.org X-archive-position: 59974 X-ecartis-version: Ecartis v1.0.0 Sender: linux-mips-bounce@linux-mips.org Errors-to: linux-mips-bounce@linux-mips.org X-original-sender: ben@decadent.org.uk Precedence: bulk List-help: List-unsubscribe: List-software: Ecartis version 1.0.0 List-Id: linux-mips X-List-ID: linux-mips List-subscribe: List-owner: List-post: List-archive: X-list: linux-mips 3.16.48-rc1 review patch. If anyone has any objections, please let me know. ------------------ From: James Hogan commit 854236363370995a609a10b03e35fd3dc5e9e4a1 upstream. Since commit 81a76d7119f6 ("MIPS: Avoid using unwind_stack() with usermode") show_backtrace() invokes the raw backtracer when cp0_status & ST0_KSU indicates user mode to fix issues on EVA kernels where user and kernel address spaces overlap. However this is used by show_stack() which creates its own pt_regs on the stack and leaves cp0_status uninitialised in most of the code paths. This results in the non deterministic use of the raw back tracer depending on the previous stack content. show_stack() deals exclusively with kernel mode stacks anyway, so explicitly initialise regs.cp0_status to KSU_KERNEL (i.e. 0) to ensure we get a useful backtrace. Fixes: 81a76d7119f6 ("MIPS: Avoid using unwind_stack() with usermode") Signed-off-by: James Hogan Cc: linux-mips@linux-mips.org Patchwork: https://patchwork.linux-mips.org/patch/16656/ Signed-off-by: Ralf Baechle Signed-off-by: Ben Hutchings --- arch/mips/kernel/traps.c | 2 ++ 1 file changed, 2 insertions(+) --- a/arch/mips/kernel/traps.c +++ b/arch/mips/kernel/traps.c @@ -190,6 +190,8 @@ void show_stack(struct task_struct *task { struct pt_regs regs; mm_segment_t old_fs = get_fs(); + + regs.cp0_status = KSU_KERNEL; if (sp) { regs.regs[29] = (unsigned long)sp; regs.regs[31] = 0;