Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932976AbdGKOVH (ORCPT ); Tue, 11 Jul 2017 10:21:07 -0400 Received: from foss.arm.com ([217.140.101.70]:45542 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S932653AbdGKOVF (ORCPT ); Tue, 11 Jul 2017 10:21:05 -0400 From: Mark Rutland To: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org, Russell King Cc: catalin.marinas@arm.com, james.morse@arm.com, labbott@redhat.com, mark.rutland@arm.com, stable@vger.kernel.org, steve.capper@arm.com, will.deacon@arm.com, viro@zeniv.linux.org.uk, peterz@infradead.org, luto@amacapital.net Subject: [PATCH 2/2] arm: mm: abort uaccess retries upon fatal signal Date: Tue, 11 Jul 2017 15:19:23 +0100 Message-Id: <1499782763-31418-3-git-send-email-mark.rutland@arm.com> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1499782763-31418-1-git-send-email-mark.rutland@arm.com> References: <1499782763-31418-1-git-send-email-mark.rutland@arm.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1753 Lines: 43 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 Cc: Russell King Cc: stable@vger.kernel.org --- arch/arm/mm/fault.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/arch/arm/mm/fault.c b/arch/arm/mm/fault.c index ff8b0aa..42f5853 100644 --- a/arch/arm/mm/fault.c +++ b/arch/arm/mm/fault.c @@ -315,8 +315,11 @@ static inline bool access_error(unsigned int fsr, struct vm_area_struct *vma) * 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 -- 1.9.1