Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755133AbdGCNho (ORCPT ); Mon, 3 Jul 2017 09:37:44 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:34554 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755095AbdGCNhh (ORCPT ); Mon, 3 Jul 2017 09:37:37 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, James Hogan , linux-mips@linux-mips.org, Ralf Baechle Subject: [PATCH 4.4 022/101] MIPS: Avoid accidental raw backtrace Date: Mon, 3 Jul 2017 15:34:22 +0200 Message-Id: <20170703133338.222115323@linuxfoundation.org> X-Mailer: git-send-email 2.13.2 In-Reply-To: <20170703133334.237346187@linuxfoundation.org> References: <20170703133334.237346187@linuxfoundation.org> User-Agent: quilt/0.65 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1546 Lines: 45 4.4-stable 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: Greg Kroah-Hartman --- arch/mips/kernel/traps.c | 2 ++ 1 file changed, 2 insertions(+) --- a/arch/mips/kernel/traps.c +++ b/arch/mips/kernel/traps.c @@ -194,6 +194,8 @@ 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;