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=-2.8 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 6813BC6778A for ; Sun, 1 Jul 2018 16:36:56 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2A7E725313 for ; Sun, 1 Jul 2018 16:36:56 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 2A7E725313 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 S1031354AbeGAQgy (ORCPT ); Sun, 1 Jul 2018 12:36:54 -0400 Received: from mail.linuxfoundation.org ([140.211.169.12]:36108 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1031061AbeGAQgr (ORCPT ); Sun, 1 Jul 2018 12:36:47 -0400 Received: from localhost (LFbn-1-12247-202.w90-92.abo.wanadoo.fr [90.92.61.202]) by mail.linuxfoundation.org (Postfix) with ESMTPSA id 0E630A73; Sun, 1 Jul 2018 16:36:46 +0000 (UTC) From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Mark Rutland , Dan Williams , Thomas Gleixner , Linus Torvalds , Peter Zijlstra , Ingo Molnar Subject: [PATCH 4.17 001/220] x86/spectre_v1: Disable compiler optimizations over array_index_mask_nospec() Date: Sun, 1 Jul 2018 18:20:25 +0200 Message-Id: <20180701160908.329822656@linuxfoundation.org> X-Mailer: git-send-email 2.18.0 In-Reply-To: <20180701160908.272447118@linuxfoundation.org> References: <20180701160908.272447118@linuxfoundation.org> User-Agent: quilt/0.65 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 4.17-stable review patch. If anyone has any objections, please let me know. ------------------ From: Dan Williams commit eab6870fee877258122a042bfd99ee7908c40280 upstream. Mark Rutland noticed that GCC optimization passes have the potential to elide necessary invocations of the array_index_mask_nospec() instruction sequence, so mark the asm() volatile. Mark explains: "The volatile will inhibit *some* cases where the compiler could lift the array_index_nospec() call out of a branch, e.g. where there are multiple invocations of array_index_nospec() with the same arguments: if (idx < foo) { idx1 = array_idx_nospec(idx, foo) do_something(idx1); } < some other code > if (idx < foo) { idx2 = array_idx_nospec(idx, foo); do_something_else(idx2); } ... since the compiler can determine that the two invocations yield the same result, and reuse the first result (likely the same register as idx was in originally) for the second branch, effectively re-writing the above as: if (idx < foo) { idx = array_idx_nospec(idx, foo); do_something(idx); } < some other code > if (idx < foo) { do_something_else(idx); } ... if we don't take the first branch, then speculatively take the second, we lose the nospec protection. There's more info on volatile asm in the GCC docs: https://gcc.gnu.org/onlinedocs/gcc/Extended-Asm.html#Volatile " Reported-by: Mark Rutland Signed-off-by: Dan Williams Acked-by: Mark Rutland Acked-by: Thomas Gleixner Acked-by: Linus Torvalds Cc: Cc: Peter Zijlstra Fixes: babdde2698d4 ("x86: Implement array_index_mask_nospec") Link: https://lkml.kernel.org/lkml/152838798950.14521.4893346294059739135.stgit@dwillia2-desk3.amr.corp.intel.com Signed-off-by: Ingo Molnar Signed-off-by: Greg Kroah-Hartman --- arch/x86/include/asm/barrier.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) --- a/arch/x86/include/asm/barrier.h +++ b/arch/x86/include/asm/barrier.h @@ -38,7 +38,7 @@ static inline unsigned long array_index_ { unsigned long mask; - asm ("cmp %1,%2; sbb %0,%0;" + asm volatile ("cmp %1,%2; sbb %0,%0;" :"=r" (mask) :"g"(size),"r" (index) :"cc");