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 85E6FC54EE9 for ; Tue, 27 Sep 2022 21:26:51 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229453AbiI0V0t (ORCPT ); Tue, 27 Sep 2022 17:26:49 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:55042 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S232142AbiI0V0n (ORCPT ); Tue, 27 Sep 2022 17:26:43 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id D240F1E76B7; Tue, 27 Sep 2022 14:26:40 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 5F7CF61B9D; Tue, 27 Sep 2022 21:26:40 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 6A142C433C1; Tue, 27 Sep 2022 21:26:37 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1664313999; bh=xsHcZmQ5k2fouDljXp77NUkSQtGkptLx+KZKrFyMkVk=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=sWPV6fPvwau/brQJo1jcJrYLI/PzgmGw3fPY7sWSFOfBq2TqCRVGiLBgKGtPrQqqW dhDsWN4Eu842mdtbU1ipgIoZ9Xtq2z956kGZvTz0lviaKFTu0FvdJDPNngCBHDvZes UZU/OKtXCayCe+J2QnePigu59JVJhk4KFwg5ZAhXWI12Q3g8Rky6FevPJUdBJyC7Fc AMp6OlUMqjauaz1vT74piycJD6rEV/LhfI/Zs6M7yP9/kI0V7y3nB5SWF4RwTOxThI xa7T0SqV+RSRYdxJDnoEpUkcHCNuwpwKEYW+45jqg+1wBEME4xmsxyKUXn5ey6gqaF SCfBNv4K2h3fA== Date: Tue, 27 Sep 2022 16:26:32 -0500 From: "Gustavo A. R. Silva" To: Kees Cook Cc: "K. Y. Srinivasan" , Haiyang Zhang , Stephen Hemminger , Wei Liu , Dexuan Cui , linux-hyperv@vger.kernel.org, Nathan Chancellor , linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org Subject: Re: [PATCH v2] Drivers: hv: vmbus: Split memcpy of flex-array Message-ID: References: <20220927211736.3241175-1-keescook@chromium.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220927211736.3241175-1-keescook@chromium.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Sep 27, 2022 at 02:17:36PM -0700, Kees Cook wrote: > To work around a misbehavior of the compiler's ability to see into > composite flexible array structs (as detailed in the coming memcpy() > hardening series[1]), split the memcpy() of the header and the payload > so no false positive run-time overflow warning will be generated. This > results in the already inlined memcpy getting unrolled a little more, > which very slightly increases text size: > > $ size drivers/hv/vmbus_drv.o.before drivers/hv/vmbus_drv.o > text data bss dec hex filename > 22968 5239 232 28439 6f17 drivers/hv/vmbus_drv.o.before > 23032 5239 232 28503 6f57 drivers/hv/vmbus_drv.o > > Avoids the run-time false-positive warning: > > memcpy: detected field-spanning write (size 212) of single field "&ctx->msg" at drivers/hv/vmbus_drv.c:1133 (size 16) > > [1] https://lore.kernel.org/linux-hardening/20220901065914.1417829-2-keescook@chromium.org/ > > Cc: "K. Y. Srinivasan" > Cc: Haiyang Zhang > Cc: Stephen Hemminger > Cc: Wei Liu > Cc: Dexuan Cui > Cc: linux-hyperv@vger.kernel.org > Reported-by: Nathan Chancellor > Reported-by: "Gustavo A. R. Silva" > Tested-by: Nathan Chancellor > Signed-off-by: Kees Cook Reviewed-by: Gustavo A. R. Silva Thanks! -- Gustavo > --- > v2: - fix commit log, add tags and exact warning test from Nathan > v1: https://lore.kernel.org/lkml/20220924030741.3345349-1-keescook@chromium.org > --- > drivers/hv/vmbus_drv.c | 3 ++- > 1 file changed, 2 insertions(+), 1 deletion(-) > > diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c > index 23c680d1a0f5..9b111a8262e3 100644 > --- a/drivers/hv/vmbus_drv.c > +++ b/drivers/hv/vmbus_drv.c > @@ -1131,7 +1131,8 @@ void vmbus_on_msg_dpc(unsigned long data) > return; > > INIT_WORK(&ctx->work, vmbus_onmessage_work); > - memcpy(&ctx->msg, &msg_copy, sizeof(msg->header) + payload_size); > + ctx->msg.header = msg_copy.header; > + memcpy(&ctx->msg.payload, msg_copy.u.payload, payload_size); > > /* > * The host can generate a rescind message while we > -- > 2.34.1 >