From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dave Martin Subject: Re: [PATCH v2 05/12] arm64: Basic Branch Target Identification support Date: Fri, 11 Oct 2019 16:32:26 +0100 Message-ID: <20191011153225.GL27757@arm.com> References: <1570733080-21015-1-git-send-email-Dave.Martin@arm.com> <1570733080-21015-6-git-send-email-Dave.Martin@arm.com> <20191011151028.GE33537@lakrids.cambridge.arm.com> <4e09ca54-f353-9448-64ed-4ba1e38c6ebc@linaro.org> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <4e09ca54-f353-9448-64ed-4ba1e38c6ebc@linaro.org> Sender: linux-kernel-owner@vger.kernel.org To: Richard Henderson Cc: Mark Rutland , Paul Elliott , Peter Zijlstra , Catalin Marinas , Will Deacon , Yu-cheng Yu , Amit Kachhap , Vincenzo Frascino , linux-arch@vger.kernel.org, Eugene Syromiatnikov , Szabolcs Nagy , "H.J. Lu" , Andrew Jones , Kees Cook , Arnd Bergmann , Jann Horn , Kristina =?utf-8?Q?Mart=C5=A1enko?= , Mark Brown , Thomas Gleixner , linux-arm-kernel@lists.infradead.org, Fl List-Id: linux-arch.vger.kernel.org On Fri, Oct 11, 2019 at 11:25:33AM -0400, Richard Henderson wrote: > On 10/11/19 11:10 AM, Mark Rutland wrote: > > On Thu, Oct 10, 2019 at 07:44:33PM +0100, Dave Martin wrote: > >> @@ -730,6 +730,11 @@ static void setup_return > >> regs->regs[29] = (unsigned long)&user->next_frame->fp; > >> regs->pc = (unsigned long)ka->sa.sa_handler; > >> > >> + if (system_supports_bti()) { > >> + regs->pstate &= ~PSR_BTYPE_MASK; > >> + regs->pstate |= PSR_BTYPE_CALL; > >> + } > >> + > > > > I think we might need a comment as to what we're trying to ensure here. > > > > I was under the (perhaps mistaken) impression that we'd generate a > > pristine pstate for a signal handler, and it's not clear to me that we > > must ensure the first instruction is a target instruction. > > I think it makes sense to treat entry into a signal handler as a call. Code > that has been compiled for BTI, and whose page has been marked with PROT_BTI, > will already have the pauth/bti markup at the beginning of the signal handler > function; we might as well verify that. > > Otherwise sigaction becomes a hole by which an attacker can force execution to > start at any arbitrary address. Ack, that's the intended rationale -- I also outlined this in the commit message. Does this sound reasonable? Either way, I feel we should do this: any function in a PROT_BTI page should have a suitable landing pad. There's no reason I can see why a protection given to any other callback function should be omitted for a signal handler. Note, if the signal handler isn't in a PROT_BTI page then overriding BTYPE here will not trigger a Branch Target exception. I'm happy to drop a brief comment into the code also, once we're agreed on what the code should be doing. Cheers ---Dave From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from foss.arm.com ([217.140.110.172]:35922 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726328AbfJKPcb (ORCPT ); Fri, 11 Oct 2019 11:32:31 -0400 Date: Fri, 11 Oct 2019 16:32:26 +0100 From: Dave Martin Subject: Re: [PATCH v2 05/12] arm64: Basic Branch Target Identification support Message-ID: <20191011153225.GL27757@arm.com> References: <1570733080-21015-1-git-send-email-Dave.Martin@arm.com> <1570733080-21015-6-git-send-email-Dave.Martin@arm.com> <20191011151028.GE33537@lakrids.cambridge.arm.com> <4e09ca54-f353-9448-64ed-4ba1e38c6ebc@linaro.org> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <4e09ca54-f353-9448-64ed-4ba1e38c6ebc@linaro.org> Sender: linux-arch-owner@vger.kernel.org List-ID: To: Richard Henderson Cc: Mark Rutland , Paul Elliott , Peter Zijlstra , Catalin Marinas , Will Deacon , Yu-cheng Yu , Amit Kachhap , Vincenzo Frascino , linux-arch@vger.kernel.org, Eugene Syromiatnikov , Szabolcs Nagy , "H.J. Lu" , Andrew Jones , Kees Cook , Arnd Bergmann , Jann Horn , Kristina =?utf-8?Q?Mart=C5=A1enko?= , Mark Brown , Thomas Gleixner , linux-arm-kernel@lists.infradead.org, Florian Weimer , linux-kernel@vger.kernel.org, Sudakshina Das Message-ID: <20191011153226.e-vKWZ-XwubPI5-JX_ZU8rFVAmyfZ2RF9KxQ8d6sTIE@z> On Fri, Oct 11, 2019 at 11:25:33AM -0400, Richard Henderson wrote: > On 10/11/19 11:10 AM, Mark Rutland wrote: > > On Thu, Oct 10, 2019 at 07:44:33PM +0100, Dave Martin wrote: > >> @@ -730,6 +730,11 @@ static void setup_return > >> regs->regs[29] = (unsigned long)&user->next_frame->fp; > >> regs->pc = (unsigned long)ka->sa.sa_handler; > >> > >> + if (system_supports_bti()) { > >> + regs->pstate &= ~PSR_BTYPE_MASK; > >> + regs->pstate |= PSR_BTYPE_CALL; > >> + } > >> + > > > > I think we might need a comment as to what we're trying to ensure here. > > > > I was under the (perhaps mistaken) impression that we'd generate a > > pristine pstate for a signal handler, and it's not clear to me that we > > must ensure the first instruction is a target instruction. > > I think it makes sense to treat entry into a signal handler as a call. Code > that has been compiled for BTI, and whose page has been marked with PROT_BTI, > will already have the pauth/bti markup at the beginning of the signal handler > function; we might as well verify that. > > Otherwise sigaction becomes a hole by which an attacker can force execution to > start at any arbitrary address. Ack, that's the intended rationale -- I also outlined this in the commit message. Does this sound reasonable? Either way, I feel we should do this: any function in a PROT_BTI page should have a suitable landing pad. There's no reason I can see why a protection given to any other callback function should be omitted for a signal handler. Note, if the signal handler isn't in a PROT_BTI page then overriding BTYPE here will not trigger a Branch Target exception. I'm happy to drop a brief comment into the code also, once we're agreed on what the code should be doing. Cheers ---Dave 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 12800C47404 for ; Fri, 11 Oct 2019 15:32:42 +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 DF25D2089F for ; Fri, 11 Oct 2019 15:32:41 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="ruiJj9q1" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DF25D2089F 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=fybCkFs4Ed8LUfjxevKMVRRqKJeaMFhrqfFwPhNplaA=; b=ruiJj9q1UT2MJZ BA6JD5gVGAiWnmmU2zayapmzql1GaFPVvqtc/6QOOog/egy/+2f0L4/QL+/Mq6JTtcA2sNYhFlg30 NMmlVRwdVWRHI0d2gFLadFv09PPBOjMKWqn5CGTupiAnUN4hkOoIObo5oOAtwLc9tb4drtNbNqEfL H1M73NwtU8lN5NQjGo31apSsyqNFThihJjclbffx+BODXz+9ekahJaWAWMWP/Ujz6T673op7nyTQJ eQ6gL+yZUDPfKDaP8PYl3msadQLFR6naiRzai8UhmLszTnZbffjds2OFvqeqQovrVlWiJPVn169QI OkykHJo74Dc1O0zg8FfQ==; 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 1iIwuA-0003Cj-8a; Fri, 11 Oct 2019 15:32:34 +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 1iIwu7-0003CD-Ob for linux-arm-kernel@lists.infradead.org; Fri, 11 Oct 2019 15:32:33 +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 2272A142F; Fri, 11 Oct 2019 08:32:31 -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 3A6D93F68E; Fri, 11 Oct 2019 08:32:28 -0700 (PDT) Date: Fri, 11 Oct 2019 16:32:26 +0100 From: Dave Martin To: Richard Henderson Subject: Re: [PATCH v2 05/12] arm64: Basic Branch Target Identification support Message-ID: <20191011153225.GL27757@arm.com> References: <1570733080-21015-1-git-send-email-Dave.Martin@arm.com> <1570733080-21015-6-git-send-email-Dave.Martin@arm.com> <20191011151028.GE33537@lakrids.cambridge.arm.com> <4e09ca54-f353-9448-64ed-4ba1e38c6ebc@linaro.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <4e09ca54-f353-9448-64ed-4ba1e38c6ebc@linaro.org> 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-20191011_083231_843679_00D62E3D X-CRM114-Status: GOOD ( 20.10 ) 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: Mark Rutland , Paul Elliott , Peter Zijlstra , Catalin Marinas , Will Deacon , Andrew Jones , Amit Kachhap , Vincenzo Frascino , linux-arch@vger.kernel.org, Eugene Syromiatnikov , Szabolcs Nagy , "H.J. Lu" , Yu-cheng Yu , Kees Cook , Arnd Bergmann , Jann Horn , Kristina =?utf-8?Q?Mart=C5=A1enko?= , Mark Brown , Thomas Gleixner , linux-arm-kernel@lists.infradead.org, Florian Weimer , linux-kernel@vger.kernel.org, Sudakshina Das 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 Fri, Oct 11, 2019 at 11:25:33AM -0400, Richard Henderson wrote: > On 10/11/19 11:10 AM, Mark Rutland wrote: > > On Thu, Oct 10, 2019 at 07:44:33PM +0100, Dave Martin wrote: > >> @@ -730,6 +730,11 @@ static void setup_return > >> regs->regs[29] = (unsigned long)&user->next_frame->fp; > >> regs->pc = (unsigned long)ka->sa.sa_handler; > >> > >> + if (system_supports_bti()) { > >> + regs->pstate &= ~PSR_BTYPE_MASK; > >> + regs->pstate |= PSR_BTYPE_CALL; > >> + } > >> + > > > > I think we might need a comment as to what we're trying to ensure here. > > > > I was under the (perhaps mistaken) impression that we'd generate a > > pristine pstate for a signal handler, and it's not clear to me that we > > must ensure the first instruction is a target instruction. > > I think it makes sense to treat entry into a signal handler as a call. Code > that has been compiled for BTI, and whose page has been marked with PROT_BTI, > will already have the pauth/bti markup at the beginning of the signal handler > function; we might as well verify that. > > Otherwise sigaction becomes a hole by which an attacker can force execution to > start at any arbitrary address. Ack, that's the intended rationale -- I also outlined this in the commit message. Does this sound reasonable? Either way, I feel we should do this: any function in a PROT_BTI page should have a suitable landing pad. There's no reason I can see why a protection given to any other callback function should be omitted for a signal handler. Note, if the signal handler isn't in a PROT_BTI page then overriding BTYPE here will not trigger a Branch Target exception. I'm happy to drop a brief comment into the code also, once we're agreed on what the code should be doing. Cheers ---Dave _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel