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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 3D064C433EF for ; Wed, 22 Jun 2022 11:23:02 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S236577AbiFVLXA (ORCPT ); Wed, 22 Jun 2022 07:23:00 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:37498 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1357718AbiFVLWr (ORCPT ); Wed, 22 Jun 2022 07:22:47 -0400 Received: from pandora.armlinux.org.uk (pandora.armlinux.org.uk [IPv6:2001:4d48:ad52:32c8:5054:ff:fe00:142]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 1DC283EF16 for ; Wed, 22 Jun 2022 04:21:22 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=armlinux.org.uk; s=pandora-2019; h=Sender:In-Reply-To:Content-Type: MIME-Version:References:Message-ID:Subject:Cc:To:From:Date:Reply-To: Content-Transfer-Encoding:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Id: List-Help:List-Unsubscribe:List-Subscribe:List-Post:List-Owner:List-Archive; bh=3PSaIfRzJISZsO0VEI6XQXwgCB4DT0qytDuqsciBimk=; b=uAnOZLdQ0Y1vfpR1o2AfyrXmnS Hy6+YWGSkQPXZeiiqK0yHniTAFTDEDImcVW2mAbAVbNoVaX1lDBHZkRG7YGB+l7FaiITvdM5WCEMR o5BQRTMk8eEXAqqxJtIcF4sCfyBYFCiqXJwfRXv/ujdtqKw+EsPGfaTkFCgh0ibtDBVHb+Ww+TDC6 gdmOwZW/CeWkfulvlMEa2XOOHXx22zMaju+XEM+ZP1bAjlVMzTo36P+X8iaiHzCgquFJkJKFvuLld /sNs/83k6Ph3VkyvgYfBBinzTCuoQR5r+IjxEAMlLqP9SDO3nfXwpErD81bmvXA7I/r+4MN/sKxW8 y1iFl7Fw==; Received: from shell.armlinux.org.uk ([fd8f:7570:feb6:1:5054:ff:fe00:4ec]:32978) by pandora.armlinux.org.uk with esmtpsa (TLS1.3) tls TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384 (Exim 4.94.2) (envelope-from ) id 1o3yQB-0003So-Na; Wed, 22 Jun 2022 12:21:19 +0100 Received: from linux by shell.armlinux.org.uk with local (Exim 4.94.2) (envelope-from ) id 1o3yQ8-0007Nl-NU; Wed, 22 Jun 2022 12:21:16 +0100 Date: Wed, 22 Jun 2022 12:21:16 +0100 From: "Russell King (Oracle)" To: Tetsuo Handa Cc: Tony Lindgren , LKML , Linux ARM Subject: Re: [PATCH] ARM: spectre-v2: fix smp_processor_id() warning Message-ID: References: <795c9463-452e-bf64-1cc0-c318ccecb1da@I-love.SAKURA.ne.jp> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <795c9463-452e-bf64-1cc0-c318ccecb1da@I-love.SAKURA.ne.jp> Sender: Russell King (Oracle) Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Jun 22, 2022 at 03:49:21PM +0900, Tetsuo Handa wrote: > syzbot complains smp_processor_id() from harden_branch_predictor() > from page fault path [1]. Explicitly disable preemption and use > raw_smp_processor_id(). > > Link: https://syzkaller.appspot.com/bug?extid=a7ee43e564223f195c84 [1] > Reported-by: syzbot > Fixes: f5fe12b1eaee220c ("ARM: spectre-v2: harden user aborts in kernel space") > Signed-off-by: Tetsuo Handa This may "fix" the warning, but... > --- > This patch is completely untested. > > arch/arm/include/asm/system_misc.h | 7 +++++-- > 1 file changed, 5 insertions(+), 2 deletions(-) > > diff --git a/arch/arm/include/asm/system_misc.h b/arch/arm/include/asm/system_misc.h > index 98b37340376b..a92446769acd 100644 > --- a/arch/arm/include/asm/system_misc.h > +++ b/arch/arm/include/asm/system_misc.h > @@ -20,8 +20,11 @@ typedef void (*harden_branch_predictor_fn_t)(void); > DECLARE_PER_CPU(harden_branch_predictor_fn_t, harden_branch_predictor_fn); > static inline void harden_branch_predictor(void) > { > - harden_branch_predictor_fn_t fn = per_cpu(harden_branch_predictor_fn, > - smp_processor_id()); > + harden_branch_predictor_fn_t fn; > + > + preempt_disable_notrace(); > + fn = per_cpu(harden_branch_predictor_fn, raw_smp_processor_id()); > + preempt_enable_no_resched_notrace(); > if (fn) > fn(); The idea is to get the function for the specific CPU, and then to run it _on_ that CPU, and in theory the CPU that took the fault. However, I seem to remember there are issues trying to achieve that, and I don't have a solution for it. -- RMK's Patch system: https://www.armlinux.org.uk/developer/patches/ FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!