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=-6.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,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 21AC3C433E0 for ; Mon, 1 Jun 2020 18:00:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id F03472065C for ; Mon, 1 Jun 2020 18:00:35 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1591034436; bh=oqkKnpN3JQgcqYTFZVsmVD/urZXJAlIzlMfHX9kho9E=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=CIXICuMwNopqcBWyy2o2Ocv/9VM8UwFFFcIjuyt+n3HjIhXxofD1RAA/4Bg3RmSIS cM61AC6ULlsBMxj41FaMk5S8Cpvsgo0NiS6RQf6tZdSiHViFZWb0jglB/U6N19p0IK F0O7HSLVJBtc8pylliS4WAKF7ygeKYdo/Na9nfTw= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1729660AbgFASAf (ORCPT ); Mon, 1 Jun 2020 14:00:35 -0400 Received: from mail.kernel.org ([198.145.29.99]:42806 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729604AbgFASAK (ORCPT ); Mon, 1 Jun 2020 14:00:10 -0400 Received: from localhost (83-86-89-107.cable.dynamic.v4.ziggo.nl [83.86.89.107]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 4CAB22073B; Mon, 1 Jun 2020 18:00:09 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1591034409; bh=oqkKnpN3JQgcqYTFZVsmVD/urZXJAlIzlMfHX9kho9E=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=Wh6z/EcFQIUVRech6ZSk8ZCF1bi1Pn+4q2RxP+CaNtJhfus0TO0lmAKialOHo7a+m SMPgq15avqcRG3vC2gjeJM6piOCo+75kRlL7be1R9uUpZyfniwCYzGCF5AScAZ9D/R I6qihXpu4J9VKCVxjK/PXJMZE6n2WGiKhYGqF9Tc= From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Peter Zijlstra , Eric Dumazet , "David S. Miller" , Alexey Kuznetsov , Hideaki YOSHIFUJI , Jakub Kicinski , Jiri Pirko , Arvind Sankar , Jiong Wang , Yuqi Jin , Shaokun Zhang Subject: [PATCH 4.14 04/77] net: revert "net: get rid of an signed integer overflow in ip_idents_reserve()" Date: Mon, 1 Jun 2020 19:53:09 +0200 Message-Id: <20200601174017.232490389@linuxfoundation.org> X-Mailer: git-send-email 2.26.2 In-Reply-To: <20200601174016.396817032@linuxfoundation.org> References: <20200601174016.396817032@linuxfoundation.org> User-Agent: quilt/0.66 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Yuqi Jin [ Upstream commit a6211caa634da39d861a47437ffcda8b38ef421b ] Commit adb03115f459 ("net: get rid of an signed integer overflow in ip_idents_reserve()") used atomic_cmpxchg to replace "atomic_add_return" inside the function "ip_idents_reserve". The reason was to avoid UBSAN warning. However, this change has caused performance degrade and in GCC-8, fno-strict-overflow is now mapped to -fwrapv -fwrapv-pointer and signed integer overflow is now undefined by default at all optimization levels[1]. Moreover, it was a bug in UBSAN vs -fwrapv /-fno-strict-overflow, so Let's revert it safely. [1] https://gcc.gnu.org/gcc-8/changes.html Suggested-by: Peter Zijlstra Suggested-by: Eric Dumazet Cc: "David S. Miller" Cc: Alexey Kuznetsov Cc: Hideaki YOSHIFUJI Cc: Jakub Kicinski Cc: Jiri Pirko Cc: Arvind Sankar Cc: Peter Zijlstra Cc: Eric Dumazet Cc: Jiong Wang Signed-off-by: Yuqi Jin Signed-off-by: Shaokun Zhang Signed-off-by: David S. Miller Signed-off-by: Greg Kroah-Hartman --- net/ipv4/route.c | 14 ++++++-------- 1 file changed, 6 insertions(+), 8 deletions(-) --- a/net/ipv4/route.c +++ b/net/ipv4/route.c @@ -499,18 +499,16 @@ u32 ip_idents_reserve(u32 hash, int segs atomic_t *p_id = ip_idents + hash % IP_IDENTS_SZ; u32 old = ACCESS_ONCE(*p_tstamp); u32 now = (u32)jiffies; - u32 new, delta = 0; + u32 delta = 0; if (old != now && cmpxchg(p_tstamp, old, now) == old) delta = prandom_u32_max(now - old); - /* Do not use atomic_add_return() as it makes UBSAN unhappy */ - do { - old = (u32)atomic_read(p_id); - new = old + delta + segs; - } while (atomic_cmpxchg(p_id, old, new) != old); - - return new - segs; + /* If UBSAN reports an error there, please make sure your compiler + * supports -fno-strict-overflow before reporting it that was a bug + * in UBSAN, and it has been fixed in GCC-8. + */ + return atomic_add_return(segs + delta, p_id) - segs; } EXPORT_SYMBOL(ip_idents_reserve);