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=-4.0 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_PASS,URIBL_BLOCKED autolearn=ham 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 3ACA4C4360F for ; Thu, 4 Apr 2019 14:08:04 +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 058612082E for ; Thu, 4 Apr 2019 14:08:04 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="lMK1CDVm" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 058612082E 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=8nkhmRa/2YAPw7kscH0/KUlW1jmiG2ZYYUlH0vA6Qf0=; b=lMK1CDVm4EdsPH QjAYhaJvcbt2ifQX0y4dSPk1PNEzou75xPYaAxb4OsLjbBYVRZQFLLulO6kyE7xuonR0NsN0+9hKo JN+T9uz6lCXIEa44lrV8aqwAEBy0J+SH6ekyoYe/+Jkgz2OF7/6t9FikE7KiRfGNudYao4klpGRpu cn3zEz2o3fmeOZ3Jgkppa47/Bzpch0Yx4MzIRPi2MmNuHQloFz0cGAki1mPw2KUFDIahEPuMIhOjU Hx4ZVuPTjSJ0Ac2UJgPvkNssu85kvBo51w3+XVowYchlBkCWa3hVY08FkrN1ZCgt/O/lP4z32wStj hikIa1LVmzf31VkvJkMQ==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1hC323-0006HR-Bv; Thu, 04 Apr 2019 14:07:55 +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 4.90_1 #2 (Red Hat Linux)) id 1hC31w-0006H5-Rt for linux-arm-kernel@lists.infradead.org; Thu, 04 Apr 2019 14:07:53 +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 CF7A1169E; Thu, 4 Apr 2019 07:07:45 -0700 (PDT) Received: from [10.1.196.72] (e119884-lin.cambridge.arm.com [10.1.196.72]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 116903F59C; Thu, 4 Apr 2019 07:07:44 -0700 (PDT) Subject: Re: [PATCH v3 4/4] arm64: compat: Add KUSER_HELPERS config option To: Catalin Marinas , Will Deacon References: <20190402162757.13491-1-vincenzo.frascino@arm.com> <20190402162757.13491-5-vincenzo.frascino@arm.com> <20190404100847.GB43584@arrakis.emea.arm.com> From: Vincenzo Frascino Message-ID: Date: Thu, 4 Apr 2019 15:07:43 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: <20190404100847.GB43584@arrakis.emea.arm.com> Content-Language: en-US X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190404_070748_924998_6D980FCC X-CRM114-Status: GOOD ( 22.74 ) 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: Mark Rutland , 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 On 04/04/2019 11:08, Catalin Marinas wrote: > On Tue, Apr 02, 2019 at 05:27:57PM +0100, Vincenzo Frascino wrote: >> diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig >> index 7e34b9eba5de..aa28884a2376 100644 >> --- a/arch/arm64/Kconfig >> +++ b/arch/arm64/Kconfig >> @@ -1494,6 +1494,34 @@ config COMPAT >> >> If you want to execute 32-bit userspace applications, say Y. >> >> +config KUSER_HELPERS >> + bool "Enable kuser helpers page for 32 bit applications." >> + depends on COMPAT >> + default y >> + help >> + Warning: disabling this option may break 32-bit user programs. >> + >> + Provide kuser helpers to compat tasks. The kernel provides >> + helper code to userspace in read only form at a fixed location >> + to allow userspace to be independent of the CPU type fitted to >> + the system. This permits binaries to be run on ARMv4 through >> + to ARMv8 without modification. >> + >> + See Documentation/arm/kernel_user_helpers.txt for details. >> + >> + However, the fixed address nature of these helpers can be used >> + by ROP (return orientated programming) authors when creating >> + exploits. >> + >> + If all of the binaries and libraries which run on your platform >> + are built specifically for your platform, and make no use of >> + these helpers, then you can turn this option off to hinder >> + such exploits. However, in that case, if a binary or library >> + relying on those helpers is run, it will not function correctly. >> + >> + Say N here only if you are absolutely certain that you do not >> + need these helpers; otherwise, the safe option is to say Y. > > In order to close the potential issue with the user unmapping the > vectors page in the 64K configuration, we'd need the change below as > well (on top of the TASK_SIZE_32 patch I queued for -rc4). > > diff --git a/arch/arm64/include/asm/processor.h b/arch/arm64/include/asm/processor.h > index 228af56ece48..fcd0e691b1ea 100644 > --- a/arch/arm64/include/asm/processor.h > +++ b/arch/arm64/include/asm/processor.h > @@ -57,7 +57,7 @@ > #define TASK_SIZE_64 (UL(1) << vabits_user) > > #ifdef CONFIG_COMPAT > -#ifdef CONFIG_ARM64_64K_PAGES > +#if defined(CONFIG_ARM64_64K_PAGES) && defined(CONFIG_KUSER_HELPERS) > /* > * With CONFIG_ARM64_64K_PAGES enabled, the last page is occupied > * by the compat vectors page. > I agree, this change is required when the new config option is added. Do you want me to send an additional patch or will this be folded with the existing series? -- Regards, Vincenzo _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel