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 498FCC54EE9 for ; Tue, 27 Sep 2022 20:47:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S232322AbiI0Uq7 (ORCPT ); Tue, 27 Sep 2022 16:46:59 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:38490 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S233247AbiI0Uqm (ORCPT ); Tue, 27 Sep 2022 16:46:42 -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 A0D5110250F; Tue, 27 Sep 2022 13:46:24 -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 3AFAE61BA0; Tue, 27 Sep 2022 20:46:24 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 0E2F5C433D6; Tue, 27 Sep 2022 20:46:23 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1664311583; bh=Sf7VqaaR4EHHX4vlNDI8Uh3V4OoviqEGs4OJjkuPMvE=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=KEZNNzr3KpkbCjZX/ZJvREb7swZiFyJmXl/NY8R03swHRszivrMyt8UXetSuBhtXd 5oTFBlMOpoM0xPzKElfZiZ9HqsDOEdXMaH58puZj0ftn0AH1999qKgdglrfiMjpme6 OlsOQXgXmF1Fgk9j/Uc81h8vjUF1GEEYgOC/jQGh6dulYlyL8D9WfRinK06JqPkSlB 7RSlS+UXGulwqb/XN3WfsCluvdhhkx06VP3KejufHndo5WGag9Hg0Usn6FALCWBgtr xCt5qZaraQDWoDHrHh671GeaD5i0Uiq8rwG1rc8BtPTKfa80o0mpStizA7VaRy0iCK uBHYh5WuJ9KBA== Date: Tue, 27 Sep 2022 13:46:21 -0700 From: Nathan Chancellor To: Kees Cook Cc: "K. Y. Srinivasan" , Haiyang Zhang , Stephen Hemminger , Wei Liu , Dexuan Cui , linux-hyperv@vger.kernel.org, "Gustavo A. R. Silva" , linux-kernel@vger.kernel.org, linux-hardening@vger.kernel.org Subject: Re: [PATCH] Drivers: hv: vmbus: Split memcpy of flex-array Message-ID: References: <20220924030741.3345349-1-keescook@chromium.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20220924030741.3345349-1-keescook@chromium.org> Precedence: bulk List-ID: X-Mailing-List: linux-hardening@vger.kernel.org On Fri, Sep 23, 2022 at 08:07:41PM -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. As it > turns out, this appears to actually reduce the 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 > > [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" > Signed-off-by: Kees Cook I was waiting for another -next update to test this in WSL2; now that said update has happened, I can see that this does resolve the runtime warning that I saw. Tested-by: Nathan Chancellor > --- > 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 > >