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,URIBL_BLOCKED,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 6DF18C83003 for ; Wed, 29 Apr 2020 08:39:02 +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 284B020731 for ; Wed, 29 Apr 2020 08:39:02 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="KQk5KWBz" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 284B020731 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=FVeMyvLYwERHDA/9pbcLfWDwAPNDZgGYX2Lrwn1/wx8=; b=KQk5KWBziRo4TYHXgFOx7w69+ YW/5cI3RUhbHCMQD2vAcCuUXbQuclTIujZacTA23Rn9Cu48aVgnJl6ze4zDNpS+56aaAkXFrnDUH+ Z+EUjXLuj0pbjucaeyB8tgDtZdhA7MS+8Try0UdeZ7OmpMfWdb8UKz/s+WF5mVkNpdCAGX1QVZVwG Nx4FmvE2HKfXxx1PBrSbd9n4bW7R7H/2j1kD/DHiLM/wI78DEhSfIqnqfZyGjJSJ1UrUeXRTK1756 7dt09VwW1akU3p2uCW/2MvU4fUVGLn/lToB9qhhxPBwPF+5q7e49FNy4jh8koEJHJPv9luKaIiqp0 m8iaOnMeQ==; 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 1jTiFB-0004jy-I8; Wed, 29 Apr 2020 08:39:01 +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 1jTiF7-0004iy-Se for linux-arm-kernel@lists.infradead.org; Wed, 29 Apr 2020 08:38:59 +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 100F6C14; Wed, 29 Apr 2020 01:38:57 -0700 (PDT) Received: from [10.57.22.235] (unknown [10.57.22.235]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 5BCC33F305; Wed, 29 Apr 2020 01:38:54 -0700 (PDT) Subject: Re: [PATCH] arm64: Optimize ptrauth by enabling it for non-leaf functions To: Mark Rutland , Will Deacon References: <1586856741-26839-1-git-send-email-amit.kachhap@arm.com> <20200414100033.GA26395@willie-the-truck> <20200414101649.GC1278@C02TD0UTHF1T.local> <20200414110056.GB26395@willie-the-truck> <20200414110922.GC2486@C02TD0UTHF1T.local> <20200414131005.GA28750@willie-the-truck> <20200414140749.GI2486@C02TD0UTHF1T.local> From: Amit Kachhap Message-ID: <617b2851-7a59-37cb-a0f5-e6ef4995bb66@arm.com> Date: Wed, 29 Apr 2020 14:08:30 +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: <20200414140749.GI2486@C02TD0UTHF1T.local> Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200429_013857_967294_E390F47E X-CRM114-Status: GOOD ( 19.06 ) 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 , Vincenzo Frascino , linux-arm-kernel@lists.infradead.org, Daniel Kiss 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 Will/Mark, On 4/14/20 7:37 PM, Mark Rutland wrote: > On Tue, Apr 14, 2020 at 02:10:06PM +0100, Will Deacon wrote: >> On Tue, Apr 14, 2020 at 12:09:22PM +0100, Mark Rutland wrote: >>> On Tue, Apr 14, 2020 at 12:00:56PM +0100, Will Deacon wrote: >>>> On Tue, Apr 14, 2020 at 11:16:49AM +0100, Mark Rutland wrote: >>>>> 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. >>>> >>>> That makes some sense, but doesn't it also mean you can jump into the middle >>>> of a leaf function and it will happily return to whatever sits in LR? >>> >>> If you can do that, you've already subverted control flow, and can >>> probably do the same for a regular function, since for: >>> >>> | AUTIASP >>> | RET >>> >>> ... you can just jump to the RET instead. >> >> Perhaps, but it's not at all clear to me that being able to jump over the >> AUT instruction is just as easy or useful as being able to jump into the >> middle of a leaf function, which might act as a form of gadget. The commit >> message is quite bold in saying "[this] is not useful from security point >> of view". I re-worded the commit log and posted the V2 version. Cheers, Amit > > Ah, I see. > > You're right that this would give some number of potentially useful > gadgets. > >> How would this interact with BTI? Would we need to have different landing >> pads for leaf functions? > > IIRC the compiler would emit a BTI instruction where the PACIASP would > have been, unless the function were only ever called directly in which > case the BTI can also be omitted. > > For functions that can only be called directly, this prevents the whole > function (which might not be AAPCS compliant) from being a gadget. For > functions that can be called indirectly, the only saving is the omission > of AUTIASP, which I suspect is not a significant saving. > > The tradeoff isn't clear to me. > > Thanks, > Mark. > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel