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,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 6C960C43381 for ; Mon, 1 Apr 2019 14:49:11 +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 3B7ED20840 for ; Mon, 1 Apr 2019 14:49:11 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="RdxY6amy" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 3B7ED20840 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=L1dL1G67QTatFyGGmYSe2JBWy6JaaIoNzJEeBVn/h50=; b=RdxY6amypnn2C/ ut3/2AN5HnHgnFYgiFDEP+LaAHcEAZRbPk65kygn+0idsiVvMCgr7z1pXEYfAdmIWq9EQdb6oj4rj 3uE7qjblnxVRCdnQl08N+oR52eUtR1Bkz+42GXjdTkjkLQsWTswam99dFZjPQJpuEUL/5Zfi0bE9r anP0PrRPVpvKOI/Z5pw9OZ1a2GDR1Ih48PFVZM5cjuJygUfN1oBBS7+QNHRkq8cdM2BGyf3Rd0/eo kRDsO86DZAF3K+vyY61343h0rHr0d8N1g8AT6epfZk833bliovtiEEl7H7v3Q4rCPdPHDIr7uSVLZ yhKEvzjv75RXz40tBkCw==; 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 1hAyFD-00080H-U6; Mon, 01 Apr 2019 14:49:03 +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 1hAyFA-0007zo-64 for linux-arm-kernel@lists.infradead.org; Mon, 01 Apr 2019 14:49:01 +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 C15A1A78; Mon, 1 Apr 2019 07:48:59 -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 B14543F690; Mon, 1 Apr 2019 07:48:58 -0700 (PDT) Date: Mon, 1 Apr 2019 15:48:56 +0100 From: Catalin Marinas To: Vincenzo Frascino Subject: Re: [PATCH 4/4] arm64: compat: Add KUSER_HELPERS config option Message-ID: <20190401144855.GJ14874@arrakis.emea.arm.com> References: <20190401112025.40807-1-vincenzo.frascino@arm.com> <20190401112025.40807-5-vincenzo.frascino@arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20190401112025.40807-5-vincenzo.frascino@arm.com> 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-20190401_074900_231092_5A97F900 X-CRM114-Status: GOOD ( 19.85 ) 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: linux-arch@vger.kernel.org, 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 Mon, Apr 01, 2019 at 12:20:25PM +0100, Vincenzo Frascino wrote: > diff --git a/arch/arm64/Kconfig b/arch/arm64/Kconfig > index 7e34b9eba5de..35c98e91bfeb 100644 > --- a/arch/arm64/Kconfig > +++ b/arch/arm64/Kconfig > @@ -1494,6 +1494,36 @@ config COMPAT > > If you want to execute 32-bit userspace applications, say Y. > > +config KUSER_HELPERS > + bool "Enable kuser helpers page for compatibility with 32 bit applications." I'd say only "Enable kuser helpers page for 32-bit applications" (my first reading of this sounded like it would be enabled for 64-bit apps to be on par with 32-bit ones). > + depends on COMPAT > + default y > + help > + Warning: disabling this option may break user programs. "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. > + > + Note: kuser helpers is disabled by default with 64K pages. Is it? > + > + Say N here only if you are absolutely certain that you do not > + need these helpers; otherwise, the safe option is to say Y. > + -- Catalin _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel