From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759662AbbIVTwV (ORCPT ); Tue, 22 Sep 2015 15:52:21 -0400 Received: from terminus.zytor.com ([198.137.202.10]:54798 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1759420AbbIVTv7 (ORCPT ); Tue, 22 Sep 2015 15:51:59 -0400 Date: Tue, 22 Sep 2015 12:48:50 -0700 From: tip-bot for Andy Lutomirski Message-ID: Cc: luto@kernel.org, hpa@zytor.com, mingo@kernel.org, linux-kernel@vger.kernel.org, tglx@linutronix.de, sasha.levin@oracle.com Reply-To: mingo@kernel.org, linux-kernel@vger.kernel.org, tglx@linutronix.de, sasha.levin@oracle.com, luto@kernel.org, hpa@zytor.com In-Reply-To: <974bc40edffdb5c2950a5c4977f821a446b76178.1442791737.git.luto@kernel.org> References: <974bc40edffdb5c2950a5c4977f821a446b76178.1442791737.git.luto@kernel.org> To: linux-tip-commits@vger.kernel.org Subject: [tip:x86/urgent] x86/nmi/64: Fix a paravirt stack-clobbering bug in the NMI code Git-Commit-ID: 47ca71ccc88972ed6af8d44dac988af59f5f1ac8 X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: 47ca71ccc88972ed6af8d44dac988af59f5f1ac8 Gitweb: http://git.kernel.org/tip/47ca71ccc88972ed6af8d44dac988af59f5f1ac8 Author: Andy Lutomirski AuthorDate: Sun, 20 Sep 2015 16:32:05 -0700 Committer: Thomas Gleixner CommitDate: Tue, 22 Sep 2015 21:43:37 +0200 x86/nmi/64: Fix a paravirt stack-clobbering bug in the NMI code The NMI entry code that switches to the normal kernel stack needs to be very careful not to clobber any extra stack slots on the NMI stack. The code is fine under the assumption that SWAPGS is just a normal instruction, but that assumption isn't really true. Use SWAPGS_UNSAFE_STACK instead. This is part of a fix for some random crashes that Sasha saw. Fixes: 9b6e6a8334d5 ("x86/nmi/64: Switch stacks on userspace NMI entry") Reported-and-tested-by: Sasha Levin Signed-off-by: Andy Lutomirski Cc: stable@vger.kernel.org Link: http://lkml.kernel.org/r/974bc40edffdb5c2950a5c4977f821a446b76178.1442791737.git.luto@kernel.org Signed-off-by: Thomas Gleixner --- arch/x86/entry/entry_64.S | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/arch/x86/entry/entry_64.S b/arch/x86/entry/entry_64.S index 404ca97..055a01d 100644 --- a/arch/x86/entry/entry_64.S +++ b/arch/x86/entry/entry_64.S @@ -1190,9 +1190,12 @@ ENTRY(nmi) * we don't want to enable interrupts, because then we'll end * up in an awkward situation in which IRQs are on but NMIs * are off. + * + * We also must not push anything to the stack before switching + * stacks lest we corrupt the "NMI executing" variable. */ - SWAPGS + SWAPGS_UNSAFE_STACK cld movq %rsp, %rdx movq PER_CPU_VAR(cpu_current_top_of_stack), %rsp