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=-5.5 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, SPF_PASS,URIBL_BLOCKED,USER_AGENT_MUTT 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 5E062C4360F for ; Thu, 4 Apr 2019 14:51:44 +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 0B44220855 for ; Thu, 4 Apr 2019 14:51:44 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="pfdKThvh" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 0B44220855 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=Mpr2LB+yzBp3vKK/CO6ZYMQcUAv5KjNnfKNBiQpzlh0=; b=pfdKThvhi3IqlT KsrWGY0sDwBOohPO5bDX6uTK6BLoQDvWUp+kzzZamzzwBM6YCAYGXbfWr3TAOR5yjAA5Lj870fgqB mbjPkhsPFaTJSMZXgTTTj3OOypu9zoSafIBvzg8IQ61Q+GnTOV3wVBx6GSYeUN6+jVCsNpPD2NjGo mHYQ19fA3sfEahTnWZBRTCXfgUFCH9D1qSONRs3z1CSgnbdL0K7ZAhODkSGf3mzuAfURivVcMic4i ukm6HJvzip5/0ZfCrYbLnMOv6+zdnhelS58CE3Oco9TrIZslUPgCLMh7pNRXhZJGsiz6xH/to6kHH dMOlc48W2RoZAf0NlvDQ==; 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 1hC3iN-0006pq-0B; Thu, 04 Apr 2019 14:51:39 +0000 Received: from foss.arm.com ([217.140.101.70]) by bombadil.infradead.org with esmtp (Exim 4.90_1 #2 (Red Hat Linux)) id 1hC3iB-0006b3-TU for linux-arm-kernel@lists.infradead.org; Thu, 04 Apr 2019 14:51:37 +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 48C35169E; Thu, 4 Apr 2019 07:51:27 -0700 (PDT) Received: from arrakis.emea.arm.com (arrakis.cambridge.arm.com [10.1.196.78]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPSA id 5D2703F59C; Thu, 4 Apr 2019 07:51:26 -0700 (PDT) Date: Thu, 4 Apr 2019 15:51:23 +0100 From: Catalin Marinas To: Vincenzo Frascino Subject: Re: [PATCH v3 4/4] arm64: compat: Add KUSER_HELPERS config option Message-ID: <20190404145123.GL43584@arrakis.emea.arm.com> References: <20190402162757.13491-1-vincenzo.frascino@arm.com> <20190402162757.13491-5-vincenzo.frascino@arm.com> <20190404100847.GB43584@arrakis.emea.arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190404_075128_310101_005142EA X-CRM114-Status: GOOD ( 23.99 ) 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 , Will Deacon , 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 Thu, Apr 04, 2019 at 03:07:43PM +0100, Vincenzo Frascino wrote: > 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? Folding it into patch 4/4 would be best but our arm64 for-next/core is based on -rc3 and the TASK_SIZE_32 reduction didn't go in yet: https://lore.kernel.org/linux-arm-kernel/20190401113014.20866-1-vincenzo.frascino@arm.com/ I can drop the TASK_SIZE_32 patch from for-next/fixes (arguably, it's not a regression and we cc stable anyway) and Will can merge it before this series. Otherwise, the fixup above can go in at 5.2-rc1. Will, any preference? -- Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel