From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S933617AbdKGAVe (ORCPT ); Mon, 6 Nov 2017 19:21:34 -0500 Received: from shadbolt.e.decadent.org.uk ([88.96.1.126]:53787 "EHLO shadbolt.e.decadent.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932814AbdKGAVb (ORCPT ); Mon, 6 Nov 2017 19:21:31 -0500 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, "Mark Rutland" , "Will Deacon" , "Catalin Marinas" , "Laura Abbott" , "James Morse" , "Steve Capper" Date: Mon, 06 Nov 2017 23:03:02 +0000 Message-ID: X-Mailer: LinuxStableQueue (scripts by bwh) Subject: [PATCH 3.16 130/294] arm64: mm: abort uaccess retries upon fatal signal 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 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 3.16.50-rc1 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 [bwh: Backported to 3.16: adjust context] Signed-off-by: Ben Hutchings --- 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 @@ -252,8 +252,11 @@ 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