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=-0.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS,URIBL_BLOCKED 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 95253C2BA19 for ; Tue, 14 Apr 2020 10:16:59 +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 63B3920732 for ; Tue, 14 Apr 2020 10:16:59 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="OsM/2Qvj" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 63B3920732 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-Transfer-Encoding:Content-Type:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:In-Reply-To:MIME-Version:References: Message-ID:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=YYKakbMQJWXDui5TsJrPBJFaSh7dd4Z6qYSYBuL3yzA=; b=OsM/2Qvj7sNyxo 1GaWexgpQeY9AL51d3KOr4EjVoYqInB/P0sYre0JvHD4v2r6NOv59E7VYaPqeKFiDT6iBQPmxPkMd JmHIL0jiKaMw6U5v/FyVjHgjFEBGfe0IZEY4jksuomOJ4+fjQK4lW1GEOkWLbn6UQYOKoo00D8jqq DkHMLaC50FNDwbrJe7aGCSBf847oBREHLskO3S4N4sMR4s+8dYCOCeH+m6TD1aLQ//lpSWzcnGjaZ Jj9QGSZEVzdRHnfouEMteHdkzor81wxtSAFOyhBPCi2/J0uGeOR7sAyiQbCgys+bccSpb0S8KJjHP FHGDYinBwfQfT9c+0D7g==; 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 1jOIci-00071h-Ov; Tue, 14 Apr 2020 10:16:56 +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 1jOIcf-00071C-RW for linux-arm-kernel@lists.infradead.org; Tue, 14 Apr 2020 10:16:55 +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 162751FB; Tue, 14 Apr 2020 03:16:53 -0700 (PDT) Received: from C02TD0UTHF1T.local (unknown [172.31.20.19]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id A674E3F6C4; Tue, 14 Apr 2020 03:16:51 -0700 (PDT) Date: Tue, 14 Apr 2020 11:16:49 +0100 From: Mark Rutland To: Will Deacon Subject: Re: [PATCH] arm64: Optimize ptrauth by enabling it for non-leaf functions Message-ID: <20200414101649.GC1278@C02TD0UTHF1T.local> References: <1586856741-26839-1-git-send-email-amit.kachhap@arm.com> <20200414100033.GA26395@willie-the-truck> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200414100033.GA26395@willie-the-truck> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200414_031653_932608_B8FA7AB1 X-CRM114-Status: GOOD ( 12.46 ) 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 , Mark Brown , James Morse , Amit Daniel Kachhap , Vincenzo Frascino , linux-arm-kernel@lists.infradead.org, Daniel Kiss Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, Apr 14, 2020 at 11:00:33AM +0100, Will Deacon wrote: > On Tue, Apr 14, 2020 at 03:02:21PM +0530, Amit Daniel Kachhap wrote: > > Compilers are optimized to not store the stack frame record for the leaf > > function in the stack so applying pointer authentication in the leaf > > function is not useful from security point of view. > > I'm missing the reasoning here -- why don't we care about leaf functions? > > Sounds like there's a performance/security trade-off that needs spelling > out and justifying with some numbers, or is it clear-cut and I'm missing > something? I believe this is because leaf functions don't store the LR to the stack (as they don't create a frame record), so it cannot be modified by a stray memory write. Amit, if you create a leaf function like: void leaf_function(void) { asm volatile("" : : : "x30"); } ... what assembly does the compiler generate when passed `-msign-return-address=non-leaf` ? * Does the compiler create a stack-frame for this function? * Where does the compiler spill x30? * Does the compiler sign the LR? Thanks, Mark. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel