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=-2.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS, 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 1222AC4321A for ; Fri, 28 Jun 2019 04:00:45 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id D8F3D2147A for ; Fri, 28 Jun 2019 04:00:44 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1561694444; bh=+VpOXo75LTdDhLhuuoxTBJKiQQ5nD94oHuo6kW9PLx8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=2Yjwe5aXzJMMx/4R2ncIungzKPn2xERxNZcrvmBfwBGchwzHjnUeFRFb6VVv2KOJ/ AmqZ6SGNFminX+JI4YeNElc4zNJ3KhjJK8OskVYhZlN/Njn+3yglnriCWgeY2e7ZSv wXn/6E30xiMiuD+EPj1kiwZTZjzzMue5tkMlgcdI= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726528AbfF1EAo (ORCPT ); Fri, 28 Jun 2019 00:00:44 -0400 Received: from mail.kernel.org ([198.145.29.99]:51114 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725873AbfF1EAo (ORCPT ); Fri, 28 Jun 2019 00:00:44 -0400 Received: from sol.localdomain (c-24-5-143-220.hsd1.ca.comcast.net [24.5.143.220]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 59CEC2070D; Fri, 28 Jun 2019 04:00:43 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1561694443; bh=+VpOXo75LTdDhLhuuoxTBJKiQQ5nD94oHuo6kW9PLx8=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=Wk+ccnTKmjcm9oInzJMB+0dNNB75ucxIeut8XOCR/Y7xP6hTrcDtH7lCEaIgtzY4v cAcXSjofCHamgYUPbORfT/k9l+Y8il+53yCqIHfw+u84tfLmFEdAugDjO/mZXUw17Z rsF9Jcub8341gulC7JgVNTnhPPrCi9vEWIdrK070= Date: Thu, 27 Jun 2019 21:00:41 -0700 From: Eric Biggers To: Jaskaran Khurana Cc: linux-security-module@vger.kernel.org, linux-kernel@vger.kernel.org, linux-integrity@vger.kernel.org, linux-fsdevel@vger.kernel.org, agk@redhat.com, snitzer@redhat.com, dm-devel@redhat.com, jmorris@namei.org, scottsh@microsoft.com, mpatocka@redhat.com, gmazyland@gmail.com Subject: Re: [RFC PATCH v5 0/1] Add dm verity root hash pkcs7 sig validation. Message-ID: <20190628040041.GB673@sol.localdomain> References: <20190619191048.20365-1-jaskarankhurana@linux.microsoft.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20190619191048.20365-1-jaskarankhurana@linux.microsoft.com> User-Agent: Mutt/1.12.1 (2019-06-15) Sender: owner-linux-security-module@vger.kernel.org Precedence: bulk List-ID: On Wed, Jun 19, 2019 at 12:10:47PM -0700, Jaskaran Khurana wrote: > This patch set adds in-kernel pkcs7 signature checking for the roothash of > the dm-verity hash tree. > The verification is to support cases where the roothash is not secured by > Trusted Boot, UEFI Secureboot or similar technologies. > One of the use cases for this is for dm-verity volumes mounted after boot, > the root hash provided during the creation of the dm-verity volume has to > be secure and thus in-kernel validation implemented here will be used > before we trust the root hash and allow the block device to be created. > > Why we are doing validation in the Kernel? > > The reason is to still be secure in cases where the attacker is able to > compromise the user mode application in which case the user mode validation > could not have been trusted. > The root hash signature validation in the kernel along with existing > dm-verity implementation gives a higher level of confidence in the > executable code or the protected data. Before allowing the creation of > the device mapper block device the kernel code will check that the detached > pkcs7 signature passed to it validates the roothash and the signature is > trusted by builtin keys set at kernel creation. The kernel should be > secured using Verified boot, UEFI Secure Boot or similar technologies so we > can trust it. > > What about attacker mounting non dm-verity volumes to run executable > code? > > This verification can be used to have a security architecture where a LSM > can enforce this verification for all the volumes and by doing this it can > ensure that all executable code runs from signed and trusted dm-verity > volumes. > > Further patches will be posted that build on this and enforce this > verification based on policy for all the volumes on the system. > I don't understand your justification for this feature. If userspace has already been pwned severely enough for the attacker to be executing arbitrary code with CAP_SYS_ADMIN (which is what the device mapper ioctls need), what good are restrictions on loading more binaries from disk? Please explain your security model. - Eric