From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70]:40596 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751263AbdH3I13 (ORCPT ); Wed, 30 Aug 2017 04:27:29 -0400 From: Mark Rutland To: stable@vger.kernel.org Cc: catalin.marinas@arm.com, will.deacon@arm.com, steve.capper@arm.com, james.morse@arm.com, labbott@redhat.com, Mark Rutland Subject: [PATCH v4.9.y] arm64: mm: abort uaccess retries upon fatal signal Date: Wed, 30 Aug 2017 09:26:09 +0100 Message-Id: <1504081569-21606-1-git-send-email-mark.rutland@arm.com> Sender: stable-owner@vger.kernel.org List-ID: 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 Cc: stable@vger.kernel.org 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 --- arch/arm64/mm/fault.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/arch/arm64/mm/fault.c b/arch/arm64/mm/fault.c index 37b95df..3952d5e 100644 --- a/arch/arm64/mm/fault.c +++ b/arch/arm64/mm/fault.c @@ -397,8 +397,11 @@ static int __kprobes do_page_fault(unsigned long addr, unsigned int esr, * 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 -- 1.9.1