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=-2.3 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,USER_AGENT_SANE_1 autolearn=no 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 4077EC28CBC for ; Wed, 6 May 2020 12:25:15 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id 103CC206DB for ; Wed, 6 May 2020 12:25:14 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="g64pFOEj" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 103CC206DB Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=arm.com Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender:Content-Type: Content-Transfer-Encoding:Cc:List-Subscribe:List-Help:List-Post:List-Archive: List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:Date:Message-ID:From: References:To:Subject:Reply-To:Content-ID:Content-Description:Resent-Date: Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID:List-Owner; bh=DKfE0Bi57u4pbeMWJ0tnOBmLvsCxQtQJoObxM8HgioY=; b=g64pFOEjVeaCKlOCOQsUq4VMD qtRxPtBADyw96oddrzJYm/3OMEcCMOvtlUHSsgftpHo70Ksx8bddXBcOGLjnoR1PtTc/je0a0+MCm 3zC1+vQ/mWicQqqYkBFSJQvo7kLfghJwbtiLg9siZlUX6vYSnlfm0InX0ewWZ/SO6jtwy6Tjn05sQ K4OYfiLFavodWCBnBY/VJE4tVENTumGu2pbfPwXijRHYJ0qkDtGTNQxfVc2pXSwmslVgt31oameS3 ymNci6/Z95209WGtvMDkba9ovoty4TAr4doEPq1cOJss8YKcBlMhjE/qlPUgudTTn1x7xjSmxde2Q LG2PdqYMw==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jWJ6t-0004zZ-HF; Wed, 06 May 2020 12:25:11 +0000 Received: from foss.arm.com ([217.140.110.172]) by bombadil.infradead.org with esmtp (Exim 4.92.3 #3 (Red Hat Linux)) id 1jWJ6q-0003ql-5h for linux-arm-kernel@lists.infradead.org; Wed, 06 May 2020 12:25:09 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.121.207.14]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 802541FB; Wed, 6 May 2020 05:25:05 -0700 (PDT) Received: from [10.57.31.214] (unknown [10.57.31.214]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 72FEA3F71F; Wed, 6 May 2020 05:25:03 -0700 (PDT) Subject: Re: [PATCH v2 01/10] arm64: bti: Support building kernel C code using BTI To: Mark Brown , Dave Martin References: <20200429211641.9279-1-broonie@kernel.org> <20200429211641.9279-2-broonie@kernel.org> <20200505165045.GQ30377@arm.com> <20200505173138.GJ5377@sirena.org.uk> From: Amit Kachhap Message-ID: <3162f9eb-a00f-5e7d-07d5-ad634ff08a16@arm.com> Date: Wed, 6 May 2020 17:54:40 +0530 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <20200505173138.GJ5377@sirena.org.uk> Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200506_052508_264629_3AE1523F X-CRM114-Status: GOOD ( 18.89 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: Catalin Marinas , Vincenzo Frascino , Will Deacon , Kees Cook , linux-arm-kernel@lists.infradead.org Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org Hi, On 5/5/20 11:01 PM, Mark Brown wrote: > On Tue, May 05, 2020 at 05:50:45PM +0100, Dave Martin wrote: >> On Wed, Apr 29, 2020 at 10:16:32PM +0100, Mark Brown wrote: > >>> +ifeq ($(CONFIG_ARM64_BTI_KERNEL),y) >>> +branch-prot-flags-$(CONFIG_CC_HAS_BRANCH_PROT_PAC_RET_BTI) := -mbranch-protection=pac-ret+leaf+bti >>> +else >>> branch-prot-flags-$(CONFIG_CC_HAS_BRANCH_PROT_PAC_RET) := -mbranch-protection=pac-ret+leaf >>> +endif > >> Is it worth a comment to explain how this differs from >> -mbranch-protection=standard, and why we're not using that here? > > There was some open discussion in a separate thread about the use of > +leaf: > > https://lore.kernel.org/linux-arm-kernel/1588149371-20310-1-git-send-email-amit.kachhap@arm.com/ > > which currently settled on leaving it in but I do agree, it probably > would be useful to document the choices we're making here. CCing Amit > as some of the discussion was off-list so I don't know all the details > there. It was decided to retain the strictest ptrauth compiler option as there is a narrow scope of ROP protection use-case in case of leaf function. Although I provided some static benefits in diluting this requirement but it was suggested to differ it till there is some run-time performance gain data for leaf functions. Yes documenting it here makes sense. Cheers, Amit Daniel > > As with the recent change to explicitly default to branch-protection=none > there's probably a case for simply being explicit about whatever we're > doing rather than relying on compiler defaults in case there are any bad > interactions with code generated for an extension that isn't fully > supported in the kernel in the future. > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel