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 44EAFC433E0 for ; Wed, 20 May 2020 11:08:40 +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 14518207F9 for ; Wed, 20 May 2020 11:08:40 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="Dps5ecKZ" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 14518207F9 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=UckmMcaCJrvvS5pQjRsCrWrK0PpXnccNI7yKVKbbx4E=; b=Dps5ecKZcn9fF5 FFynOtG9oVoMyH0u9ux0DwNvS8RvuN4kgknElMWg9riIj14q3e/TVX/KRteZ+mubmFOSKEsBp+78R jnD/cWTgXwVD5uEs5h2osA2E8ToVctNaMHBCQ8JC9kO2OFcEny0L+NNOO6RHyXnZCh9Nldy12dsiT XdNMG5bzgo1JKQf1xfO4KRtKqOX5eiMVOD/rc//zyaXoZUonPeZWOpPYveI2UUHKuGTZIjHemBhPa OUylB2c3KzOcM+1PFI1Qa6imBH6lkAAQ7LoilvcS7ZH3ljvfZ1z1jcmHIHyogQ94rRXqZDpVi4mT5 ofZ5J4ihlRXgSuHhYmzg==; 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 1jbMaV-0008VL-FI; Wed, 20 May 2020 11:08:39 +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 1jbMaS-0008Ur-Od for linux-arm-kernel@lists.infradead.org; Wed, 20 May 2020 11:08:38 +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 33D2531B; Wed, 20 May 2020 04:08:36 -0700 (PDT) Received: from arm.com (usa-sjc-imap-foss1.foss.arm.com [10.121.207.14]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 4E9B53F68F; Wed, 20 May 2020 04:08:35 -0700 (PDT) Date: Wed, 20 May 2020 12:08:33 +0100 From: Dave Martin To: Mark Brown Subject: Re: [PATCH 1/3] arm64: vdso: Don't prefix sigreturn trampoline with a BTI C instruction Message-ID: <20200520110833.GP5031@arm.com> References: <20200519121818.14511-1-will@kernel.org> <20200519121818.14511-2-will@kernel.org> <20200519123843.GJ4611@sirena.org.uk> <20200519132538.GE5031@arm.com> <20200519143500.GK4611@sirena.org.uk> <20200519145514.GH5031@arm.com> <20200519154247.GN4611@sirena.org.uk> <20200520094844.GL5031@arm.com> <20200520104653.GA4823@sirena.org.uk> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20200520104653.GA4823@sirena.org.uk> User-Agent: Mutt/1.5.23 (2014-03-12) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200520_040836_842924_C06FE27A X-CRM114-Status: GOOD ( 16.47 ) 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: Tamas Zsoldos , Will Deacon , kernel-team@android.com, 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 Wed, May 20, 2020 at 11:46:53AM +0100, Mark Brown wrote: > On Wed, May 20, 2020 at 10:48:45AM +0100, Dave Martin wrote: > > On Tue, May 19, 2020 at 04:42:47PM +0100, Mark Brown wrote: > > > On Tue, May 19, 2020 at 03:55:15PM +0100, Dave Martin wrote: > > > > > > > If BTI {nothing} allows this while disallowing all BR/BLR then we could > > > > > > use that (I can't remember what BTI {nothing} is useful for, if anything). > > > > > > > Otherwise, it's less clear what we should have here. > > > > > > I can't remember anything that distinguishes it from an explicit NOP. > > > > > I think it rejects everything other then fallthrough execution > > > > (BTYPE==0, which includes RET). I might have misunderstood something > > > > Right, but since BTI only generates an exception when BTYPE != 0 I'm > > > having trouble differentiating this from a NOP in practical terms. > > > The idea would be that if an attacker could fudge some function pointer > > to point at __kernel_rt_sigreturn, attempting to do a call via that > > pointer would still trigger a BTI trap. > > We'll get a BTI exception no matter what instruction is here so long as > it's not an appropriate BTI landing pad so unless we want to prevent one > being generated there's no need to change the instruction sequence. Or > perhaps I'm not quite getting the scenario you're thinking of? Duh, yes. I guess we're good, then. Cheers ---Dave _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel