From patchwork Thu Jan 4 15:08:26 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Will Deacon X-Patchwork-Id: 10144909 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 1078F6034B for ; Thu, 4 Jan 2018 15:10:04 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id F238C286FC for ; Thu, 4 Jan 2018 15:10:03 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id E680A28701; Thu, 4 Jan 2018 15:10:03 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-4.2 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,RCVD_IN_DNSWL_MED autolearn=ham version=3.3.1 Received: from bombadil.infradead.org (bombadil.infradead.org [65.50.211.133]) (using TLSv1.2 with cipher AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id 4D371286FC for ; Thu, 4 Jan 2018 15:10:03 +0000 (UTC) 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:MIME-Version:Cc:List-Subscribe: List-Help:List-Post:List-Archive:List-Unsubscribe:List-Id:References: In-Reply-To:Message-Id:Date:Subject:To:From:Reply-To:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Owner; bh=gYp6WUdrt3zCYayEJsPAXF3iVn/bD/Vvqh/dFf4cm9k=; b=cNs5pk8aZJNRtOuhdm/fCH+9ic 24PpfFyKdA8iGcq6IayVWempR5msun8SZ7eFGXdcSTk097xlnKSdWUoeqqq1klDjwjrAA6R4XMwGQ X8BcuFLYVG39UUcVU8/By2HK69Z2X/Fa4B/2OThUppVkdKLbv1WIMoTfb32ryp4OfGzgBeueqTBw+ 2Hf8afMDnaFJOR0rwDQtvHQ5nnmJTdJizJpVVdnoG83e2dualSSq0EIELgcoSQadL3YHD6951yXgM DTmFpDzrysqMYZ180KfJKfx9O0qU9oBYVrt2shpKlrntrtAB847MbPlAnr8o6aqHqMkUtQd8wJqsm 5oct2Z7w==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.89 #1 (Red Hat Linux)) id 1eX79b-0000I1-BX; Thu, 04 Jan 2018 15:09:59 +0000 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70] helo=foss.arm.com) by bombadil.infradead.org with esmtp (Exim 4.89 #1 (Red Hat Linux)) id 1eX78U-00084C-PH for linux-arm-kernel@lists.infradead.org; Thu, 04 Jan 2018 15:08:54 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 8CB9A15AD; Thu, 4 Jan 2018 07:08:40 -0800 (PST) Received: from edgewater-inn.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.72.51.249]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 5EBDF3F77C; Thu, 4 Jan 2018 07:08:40 -0800 (PST) Received: by edgewater-inn.cambridge.arm.com (Postfix, from userid 1000) id 852641AE0E43; Thu, 4 Jan 2018 15:08:40 +0000 (GMT) From: Will Deacon To: linux-arm-kernel@lists.infradead.org Subject: [PATCH 02/11] arm64: Kconfig: Reword UNMAP_KERNEL_AT_EL0 kconfig entry Date: Thu, 4 Jan 2018 15:08:26 +0000 Message-Id: <1515078515-13723-3-git-send-email-will.deacon@arm.com> X-Mailer: git-send-email 2.1.4 In-Reply-To: <1515078515-13723-1-git-send-email-will.deacon@arm.com> References: <1515078515-13723-1-git-send-email-will.deacon@arm.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20180104_070850_987051_4081C71A X-CRM114-Status: GOOD ( 11.74 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: lorenzo.pieralisi@arm.com, ard.biesheuvel@linaro.org, marc.zyngier@arm.com, catalin.marinas@arm.com, Will Deacon , linux-kernel@vger.kernel.org, christoffer.dall@linaro.org MIME-Version: 1.0 Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org X-Virus-Scanned: ClamAV using ClamSMTP Although CONFIG_UNMAP_KERNEL_AT_EL0 does make KASLR more robust, it's actually more useful as a mitigation against speculation attacks that can leak arbitrary kernel data to userspace through speculation. Reword the Kconfig help message to reflect this, and make the option depend on EXPERT so that it is on by default for the majority of users. Signed-off-by: Will Deacon --- arch/arm64/Kconfig | 13 ++++++------- 1 file changed, 6 insertions(+), 7 deletions(-) diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig index 3af1657fcac3..efaaa3a66b95 100644 --- a/arch/arm64/Kconfig +++ b/arch/arm64/Kconfig @@ -834,15 +834,14 @@ config FORCE_MAX_ZONEORDER 4M allocations matching the default size used by generic code. config UNMAP_KERNEL_AT_EL0 - bool "Unmap kernel when running in userspace (aka \"KAISER\")" + bool "Unmap kernel when running in userspace (aka \"KAISER\")" if EXPERT default y help - Some attacks against KASLR make use of the timing difference between - a permission fault which could arise from a page table entry that is - present in the TLB, and a translation fault which always requires a - page table walk. This option defends against these attacks by unmapping - the kernel whilst running in userspace, therefore forcing translation - faults for all of kernel space. + Speculation attacks against some high-performance processors can + be used to bypass MMU permission checks and leak kernel data to + userspace. This can be defended against by unmapping the kernel + when running in userspace, mapping it back in on exception entry + via a trampoline page in the vector table. If unsure, say Y.