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=-2.2 required=3.0 tests=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 2A458C5DF63 for ; Tue, 5 Nov 2019 19:55:02 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id E979F21D6C for ; Tue, 5 Nov 2019 19:55:01 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727262AbfKETy5 (ORCPT ); Tue, 5 Nov 2019 14:54:57 -0500 Received: from foss.arm.com ([217.140.110.172]:58000 "EHLO foss.arm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726141AbfKETy5 (ORCPT ); Tue, 5 Nov 2019 14:54:57 -0500 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 8E02A7B9; Tue, 5 Nov 2019 11:54:56 -0800 (PST) Received: from lakrids.cambridge.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 5E4523FBA1; Tue, 5 Nov 2019 01:15:53 -0800 (PST) Date: Tue, 5 Nov 2019 09:15:51 +0000 From: Mark Rutland To: Sami Tolvanen Cc: Will Deacon , Catalin Marinas , Steven Rostedt , Masami Hiramatsu , Ard Biesheuvel , Dave Martin , Kees Cook , Laura Abbott , Marc Zyngier , Nick Desaulniers , Jann Horn , Miguel Ojeda , Masahiro Yamada , clang-built-linux , Kernel Hardening , linux-arm-kernel , LKML Subject: Re: [PATCH v4 11/17] arm64: disable function graph tracing with SCS Message-ID: <20191105091301.GB4743@lakrids.cambridge.arm.com> References: <20191018161033.261971-1-samitolvanen@google.com> <20191101221150.116536-1-samitolvanen@google.com> <20191101221150.116536-12-samitolvanen@google.com> <20191104171132.GB2024@lakrids.cambridge.arm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.11.1+11 (2f07cb52) (2018-12-01) Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Nov 04, 2019 at 03:44:39PM -0800, Sami Tolvanen wrote: > On Mon, Nov 4, 2019 at 9:11 AM Mark Rutland wrote: > > Can you please elaborate on _how_ this is incompatible in the commit > > message? > > > > For example, it's not clear to me if you mean that's functionally > > incompatible, or if you're trying to remove return-altering gadgets. > > > > If there's a functional incompatibility, please spell that out a bit > > more clearly. Likewise if this is about minimizing the set of places > > that can mess with control-flow outside of usual function conventions. > > Sure, I'll add a better description in v5. In this case, the return > address is modified in the kernel stack, which means the changes are > ignored with SCS. Ok, that makes sense to me. I'd suggest something like: | The graph tracer hooks returns by modifying frame records on the | (regular) stack, but with SCS the return address is taken from the | shadow stack, and the value in the frame record has no effect. As we | don't currently have a mechanism to determine the corresponding slot | on the shadow stack (and to pass this through the ftrace | infrastructure), for now let's disable the graph tracer when SCS is | enabled. ... as I suspect with some rework of the trampoline and common ftrace code we'd be able to correctly manipulate the shadow stack for this. Similarly, if clang gained -fpatchable-funciton-etnry, we'd get that for free. Thanks, Mark. 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=-2.2 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 BB8BDC5DF60 for ; Tue, 5 Nov 2019 19:55:18 +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 6709B21D7C for ; Tue, 5 Nov 2019 19:55:18 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="f05FfKaR" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6709B21D7C 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=RbOKHFOMQFngtRLwQEEDsaRC6RvTv3E109sK4lg+etA=; b=f05FfKaRnpy5BL KZ5MsEcckCAEfIQQcRMyEpHLFRCLDG60y0QMAsFkVapL9q0ZCIv147dnYKt4HerSiOLxtvuHcaVNe VzILFm+CWGo9LVSytwhFdENr6Uu6L4yc/rP/3c+Wdc7mDovYVbYg9Ho2fC6P1nwHm72iYqrwaDnVm 2Q+Pipddm2B+ahPoiYNIysrZF2IMpBfKlG6X5VqQ/5I2r9NybnxTjeHYrfKneccLoPJOEY7+3HT6D aRoer+wHgaHQ+PoCBnlDHP2Ato5DLyxmdRc1X0qHlxFH9eWAcAX94oD11A1oHFldKSWHMOKTkoFZ8 ZmSsDK8sp1v4DljUmk6w==; 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 1iS4v7-0001VS-CD; Tue, 05 Nov 2019 19:55:17 +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 1iS4uq-00007F-P8 for linux-arm-kernel@lists.infradead.org; Tue, 05 Nov 2019 19:55:02 +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 8E02A7B9; Tue, 5 Nov 2019 11:54:56 -0800 (PST) Received: from lakrids.cambridge.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 5E4523FBA1; Tue, 5 Nov 2019 01:15:53 -0800 (PST) Date: Tue, 5 Nov 2019 09:15:51 +0000 From: Mark Rutland To: Sami Tolvanen Subject: Re: [PATCH v4 11/17] arm64: disable function graph tracing with SCS Message-ID: <20191105091301.GB4743@lakrids.cambridge.arm.com> References: <20191018161033.261971-1-samitolvanen@google.com> <20191101221150.116536-1-samitolvanen@google.com> <20191101221150.116536-12-samitolvanen@google.com> <20191104171132.GB2024@lakrids.cambridge.arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.11.1+11 (2f07cb52) (2018-12-01) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20191105_115500_856138_5A86ECD1 X-CRM114-Status: GOOD ( 15.65 ) 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: Kees Cook , Ard Biesheuvel , Masahiro Yamada , Catalin Marinas , Jann Horn , Nick Desaulniers , LKML , Steven Rostedt , Miguel Ojeda , clang-built-linux , Masami Hiramatsu , Marc Zyngier , Kernel Hardening , Laura Abbott , Will Deacon , Dave Martin , linux-arm-kernel 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 Mon, Nov 04, 2019 at 03:44:39PM -0800, Sami Tolvanen wrote: > On Mon, Nov 4, 2019 at 9:11 AM Mark Rutland wrote: > > Can you please elaborate on _how_ this is incompatible in the commit > > message? > > > > For example, it's not clear to me if you mean that's functionally > > incompatible, or if you're trying to remove return-altering gadgets. > > > > If there's a functional incompatibility, please spell that out a bit > > more clearly. Likewise if this is about minimizing the set of places > > that can mess with control-flow outside of usual function conventions. > > Sure, I'll add a better description in v5. In this case, the return > address is modified in the kernel stack, which means the changes are > ignored with SCS. Ok, that makes sense to me. I'd suggest something like: | The graph tracer hooks returns by modifying frame records on the | (regular) stack, but with SCS the return address is taken from the | shadow stack, and the value in the frame record has no effect. As we | don't currently have a mechanism to determine the corresponding slot | on the shadow stack (and to pass this through the ftrace | infrastructure), for now let's disable the graph tracer when SCS is | enabled. ... as I suspect with some rework of the trampoline and common ftrace code we'd be able to correctly manipulate the shadow stack for this. Similarly, if clang gained -fpatchable-funciton-etnry, we'd get that for free. Thanks, Mark. _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel