Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752009AbdIEHM0 (ORCPT ); Tue, 5 Sep 2017 03:12:26 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:38458 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751989AbdIEHMW (ORCPT ); Tue, 5 Sep 2017 03:12:22 -0400 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Catalin Marinas , Laura Abbott , Steve Capper , James Morse , Mark Rutland , Will Deacon Subject: [PATCH 4.12 01/27] arm64: mm: abort uaccess retries upon fatal signal Date: Tue, 5 Sep 2017 09:11:17 +0200 Message-Id: <20170905070923.317706125@linuxfoundation.org> X-Mailer: git-send-email 2.14.1 In-Reply-To: <20170905070923.265950493@linuxfoundation.org> References: <20170905070923.265950493@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: 2073 Lines: 54 4.12-stable review patch. If anyone has any objections, please let me know. ------------------ From: Mark Rutland commit 289d07a2dc6c6b6f3e4b8a62669320d99dbe6c3d upstream. When there's a fatal signal pending, arm64'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. Cc: Catalin Marinas Cc: Laura Abbott Reviewed-by: Steve Capper Tested-by: Steve Capper Reviewed-by: James Morse Tested-by: James Morse Signed-off-by: Mark Rutland Signed-off-by: Will Deacon Signed-off-by: Greg Kroah-Hartman --- arch/arm64/mm/fault.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) --- a/arch/arm64/mm/fault.c +++ b/arch/arm64/mm/fault.c @@ -397,8 +397,11 @@ 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 initial