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 B2C2AC352A3 for ; Tue, 11 Feb 2020 13:57:46 +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 6D7922086A for ; Tue, 11 Feb 2020 13:57:46 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="IIyQGEcP" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 6D7922086A 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: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=9wUa8nu56ai3QD34P7Z805hmURbIraKheOPbJoxFTjI=; b=IIyQGEcPjWu0TV fPdNBH8s8vpc71B5ZCxvmjL3UZU1nWN1P16dd9DOxvyK7+bxP2aTUPnztI0QPy0xojVt61FgsI07e SNqHkaK9MK42nujfjOTF5jAkfufIO4QQvA4tYhhzi6JHpKPKLsH33R04f2JiKTFvvKajXNvDbnm8T N5EvBY6LjbNMOSHqecJVLAOckBH4NOqNhIRFrEFFDLETt0kpCBNl9EQLT+AOh26YZLCooW/+hmEZ7 pEtXC2PNQQ5j67gvp3njc78S/8kbnAsza+Rbr13ZqrKnQSxbuegkhRejkDjyzBosygZ8qV+qhOYKN Anddir8IbfpKKotM09TQ==; 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 1j1W2e-0008DA-RC; Tue, 11 Feb 2020 13:57:32 +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 1j1W2b-0008C3-1u for linux-arm-kernel@lists.infradead.org; Tue, 11 Feb 2020 13:57:30 +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 C768030E; Tue, 11 Feb 2020 05:57:27 -0800 (PST) Received: from [10.1.196.105] (eglon.cambridge.arm.com [10.1.196.105]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 909D33F68F; Tue, 11 Feb 2020 05:57:25 -0800 (PST) Subject: Re: [PATCH v7 00/11] add support for Clang's Shadow Call Stack To: Sami Tolvanen References: <20191018161033.261971-1-samitolvanen@google.com> <20200128184934.77625-1-samitolvanen@google.com> From: James Morse Message-ID: <63517cff-4bd6-bb6c-9a54-23de4f5fbb4a@arm.com> Date: Tue, 11 Feb 2020 13:57:24 +0000 User-Agent: Mozilla/5.0 (X11; Linux aarch64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 MIME-Version: 1.0 In-Reply-To: <20200128184934.77625-1-samitolvanen@google.com> Content-Language: en-GB X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20200211_055729_140353_17FBA6E1 X-CRM114-Status: GOOD ( 16.87 ) 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 , Kees Cook , Ard Biesheuvel , Masahiro Yamada , Catalin Marinas , Jann Horn , Nick Desaulniers , linux-kernel@vger.kernel.org, Steven Rostedt , Miguel Ojeda , clang-built-linux@googlegroups.com, Masami Hiramatsu , Marc Zyngier , kernel-hardening@lists.openwall.com, Laura Abbott , Will Deacon , Dave Martin , linux-arm-kernel@lists.infradead.org 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 Hi Sami, On 28/01/2020 18:49, Sami Tolvanen wrote: > This patch series adds support for Clang's Shadow Call Stack > (SCS) mitigation, which uses a separately allocated shadow stack > to protect against return address overwrites. More information > can be found here: > > https://clang.llvm.org/docs/ShadowCallStack.html > > SCS provides better protection against traditional buffer > overflows than CONFIG_STACKPROTECTOR_*, but it should be noted > that SCS security guarantees in the kernel differ from the ones > documented for user space. The kernel must store addresses of > shadow stacks used by inactive tasks and interrupt handlers in > memory, which means an attacker capable reading and writing > arbitrary memory may be able to locate them and hijack control > flow by modifying shadow stacks that are not currently in use. > > SCS is currently supported only on arm64, where the compiler > requires the x18 register to be reserved for holding the current > task's shadow stack pointer. I found I had to add: | KBUILD_CFLAGS := $(filter-out -ffixed-x18 $(CC_FLAGS_SCS), $(KBUILD_CFLAGS)) to drivers/firmware/efi/libstub/Makefile, to get this going. I don't think there is much point supporting SCS for the EFIstub, its already isolated from the rest of the kernel's C code by the __efistub symbol prefix machinery, and trying to use it would expose us to buggy firmware at a point we can't handle it! I can send a patch if its easier for you, Thanks, James _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel