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=-10.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_HELO_NONE,SPF_PASS,USER_AGENT_GIT autolearn=unavailable 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 BCF06C433E0 for ; Mon, 8 Jun 2020 23:16:47 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 9EAD320872 for ; Mon, 8 Jun 2020 23:16:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1591658207; bh=c5eiPu2dbd+pDztLejTMF6S4xO95QJd761VA4H594WQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=m7evA+Z8a3JmZgrg1RrxhFPRvby7GN+e3oEZUxduOENKJLtWQekXjSAYKtcmLEjaz ZDLU0PWjF/em8YfnLpc5qoezU8Kh8akWAAxEFk5NmQAXpHx6nrRcLFPNIe8STKXDQZ OAdTT471TlgpSZ7zGYq1HwFDRddJlYs5ATLxHqPA= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730341AbgFHXQp (ORCPT ); Mon, 8 Jun 2020 19:16:45 -0400 Received: from mail.kernel.org ([198.145.29.99]:38104 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730314AbgFHXQm (ORCPT ); Mon, 8 Jun 2020 19:16:42 -0400 Received: from sasha-vm.mshome.net (c-73-47-72-35.hsd1.nh.comcast.net [73.47.72.35]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 0253820801; Mon, 8 Jun 2020 23:16:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1591658202; bh=c5eiPu2dbd+pDztLejTMF6S4xO95QJd761VA4H594WQ=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=pf08Ct3IzuU9LK9NxS86fP0QrMdtNw8ZPFx0sS8RCWucr4P7xZe9GyXMxqDyyU6xm VCfv/azYrk2S8xPbivldjOSm70ZVvo8bVNEQyFj3OsAlecgsFnw71NqzZ7iRdW0f7d v90FBI2eLfq5aKadVAzCx+fQ4nTvrudZHM7OS3dM= From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Yuqi Jin , Peter Zijlstra , Eric Dumazet , "David S. Miller" , Alexey Kuznetsov , Hideaki YOSHIFUJI , Jakub Kicinski , Jiri Pirko , Arvind Sankar , Jiong Wang , Shaokun Zhang , Greg Kroah-Hartman , netdev@vger.kernel.org Subject: [PATCH AUTOSEL 5.6 221/606] net: revert "net: get rid of an signed integer overflow in ip_idents_reserve()" Date: Mon, 8 Jun 2020 19:05:46 -0400 Message-Id: <20200608231211.3363633-221-sashal@kernel.org> X-Mailer: git-send-email 2.25.1 In-Reply-To: <20200608231211.3363633-1-sashal@kernel.org> References: <20200608231211.3363633-1-sashal@kernel.org> MIME-Version: 1.0 X-stable: review X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Sender: netdev-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: netdev@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(-) diff --git a/net/ipv4/route.c b/net/ipv4/route.c index ef6b70774fe1..fea6a8a11183 100644 --- a/net/ipv4/route.c +++ b/net/ipv4/route.c @@ -491,18 +491,16 @@ u32 ip_idents_reserve(u32 hash, int segs) atomic_t *p_id = ip_idents + hash % IP_IDENTS_SZ; u32 old = READ_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); -- 2.25.1