Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752444AbdILQ6x (ORCPT ); Tue, 12 Sep 2017 12:58:53 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:48722 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752396AbdILQ6q (ORCPT ); Tue, 12 Sep 2017 12:58:46 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Mark Rutland , Steve Capper , Russell King Subject: [PATCH 4.9 12/14] ARM: 8692/1: mm: abort uaccess retries upon fatal signal Date: Tue, 12 Sep 2017 09:58:26 -0700 Message-Id: <20170912165254.328027740@linuxfoundation.org> X-Mailer: git-send-email 2.14.1 In-Reply-To: <20170912165253.709627159@linuxfoundation.org> References: <20170912165253.709627159@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: 1843 Lines: 49 4.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: Mark Rutland commit 746a272e44141af24a02f6c9b0f65f4c4598ed42 upstream. When there's a fatal signal pending, arm's do_page_fault() implementation returns 0. The intent is that we'll return to the faulting userspace instruction, delivering the signal on the way. However, if we take a fatal signal during fixing up a uaccess, this results in a return to the faulting kernel instruction, which will be instantly retried, resulting in the same fault being taken forever. As the task never reaches userspace, the signal is not delivered, and the task is left unkillable. While the task is stuck in this state, it can inhibit the forward progress of the system. To avoid this, we must ensure that when a fatal signal is pending, we apply any necessary fixup for a faulting kernel instruction. Thus we will return to an error path, and it is up to that code to make forward progress towards delivering the fatal signal. Signed-off-by: Mark Rutland Reviewed-by: Steve Capper Signed-off-by: Russell King Signed-off-by: Greg Kroah-Hartman --- arch/arm/mm/fault.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) --- a/arch/arm/mm/fault.c +++ b/arch/arm/mm/fault.c @@ -314,8 +314,11 @@ retry: * signal first. We do not need to release the mmap_sem because * it would already be released in __lock_page_or_retry in * mm/filemap.c. */ - if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current)) + if ((fault & VM_FAULT_RETRY) && fatal_signal_pending(current)) { + if (!user_mode(regs)) + goto no_context; return 0; + } /* * Major/minor page fault accounting is only done on the