From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,URIBL_BLOCKED,USER_AGENT_GIT autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 89155C28CF6 for ; Wed, 1 Aug 2018 17:24:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 3FC622083D for ; Wed, 1 Aug 2018 17:24:56 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3FC622083D Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linuxfoundation.org Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2406631AbeHATLg (ORCPT ); Wed, 1 Aug 2018 15:11:36 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:51216 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2404619AbeHATLe (ORCPT ); Wed, 1 Aug 2018 15:11:34 -0400 Received: from localhost (D57E6652.static.ziggozakelijk.nl [213.126.102.82]) by mail.linuxfoundation.org (Postfix) with ESMTPSA id D824FCC3; Wed, 1 Aug 2018 17:24:51 +0000 (UTC) From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Mark Rutland , Andrey Ryabinin , Dmitry Vyukov , Ingo Molnar , Peter Zijlstra , Andrew Morton , Linus Torvalds , Sasha Levin Subject: [PATCH 4.9 012/144] kcov: ensure irq code sees a valid area Date: Wed, 1 Aug 2018 18:50:39 +0200 Message-Id: <20180801164949.807218634@linuxfoundation.org> X-Mailer: git-send-email 2.18.0 In-Reply-To: <20180801164949.023217860@linuxfoundation.org> References: <20180801164949.023217860@linuxfoundation.org> User-Agent: quilt/0.65 X-stable: review MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 4.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: Mark Rutland [ Upstream commit c9484b986ef03492357fddd50afbdd02929cfa72 ] Patch series "kcov: fix unexpected faults". These patches fix a few issues where KCOV code could trigger recursive faults, discovered while debugging a patch enabling KCOV for arch/arm: * On CONFIG_PREEMPT kernels, there's a small race window where __sanitizer_cov_trace_pc() can see a bogus kcov_area. * Lazy faulting of the vmalloc area can cause mutual recursion between fault handling code and __sanitizer_cov_trace_pc(). * During the context switch, switching the mm can cause the kcov_area to be transiently unmapped. These are prerequisites for enabling KCOV on arm, but the issues themsevles are generic -- we just happen to avoid them by chance rather than design on x86-64 and arm64. This patch (of 3): For kernels built with CONFIG_PREEMPT, some C code may execute before or after the interrupt handler, while the hardirq count is zero. In these cases, in_task() can return true. A task can be interrupted in the middle of a KCOV_DISABLE ioctl while it resets the task's kcov data via kcov_task_init(). Instrumented code executed during this period will call __sanitizer_cov_trace_pc(), and as in_task() returns true, will inspect t->kcov_mode before trying to write to t->kcov_area. In kcov_init_task() we update t->kcov_{mode,area,size} with plain stores, which may be re-ordered, torn, etc. Thus __sanitizer_cov_trace_pc() may see bogus values for any of these fields, and may attempt to write to memory which is not mapped. Let's avoid this by using WRITE_ONCE() to set t->kcov_mode, with a barrier() to ensure this is ordered before we clear t->kov_{area,size}. This ensures that any code execute while kcov_init_task() is preempted will either see valid values for t->kcov_{area,size}, or will see that t->kcov_mode is KCOV_MODE_DISABLED, and bail out without touching t->kcov_area. Link: http://lkml.kernel.org/r/20180504135535.53744-2-mark.rutland@arm.com Signed-off-by: Mark Rutland Acked-by: Andrey Ryabinin Cc: Dmitry Vyukov Cc: Ingo Molnar Cc: Peter Zijlstra Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman --- kernel/kcov.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) --- a/kernel/kcov.c +++ b/kernel/kcov.c @@ -103,7 +103,8 @@ static void kcov_put(struct kcov *kcov) void kcov_task_init(struct task_struct *t) { - t->kcov_mode = KCOV_MODE_DISABLED; + WRITE_ONCE(t->kcov_mode, KCOV_MODE_DISABLED); + barrier(); t->kcov_size = 0; t->kcov_area = NULL; t->kcov = NULL;