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=0.6 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,FSL_HELO_FAKE,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 6032AC5B57B for ; Fri, 28 Jun 2019 20:35:00 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 2D2E421670 for ; Fri, 28 Jun 2019 20:35:00 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1561754100; bh=QFyZmYCKzWAWjnce7iN2QQr+iL737LARfy//MkK70ik=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=19+Nt+RKBtdjtgFlAS8gyPhUnB9cgZdD3rWV3sgN4V4hxL02zpU7dffkdp5oaNCvC eK2BKIrgHodRRbWjnTNN57URb6HplfEKDqXGF/BZPZg4yucf17fdWgsuNLIM8C0gf3 3KjcahEIahjxj1BKxhT4h2WYCGFafcOqX6FW3rNQ= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1727212AbfF1Uez (ORCPT ); Fri, 28 Jun 2019 16:34:55 -0400 Received: from mail.kernel.org ([198.145.29.99]:55950 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727042AbfF1Uez (ORCPT ); Fri, 28 Jun 2019 16:34:55 -0400 Received: from gmail.com (unknown [104.132.1.77]) (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 43EEE20828; Fri, 28 Jun 2019 20:34:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1561754093; bh=QFyZmYCKzWAWjnce7iN2QQr+iL737LARfy//MkK70ik=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=jETG2D35PRDLc03KmfIEhyoNjKddAVpbtnqHoYwvN+y8rPMvVsdUQSoVs4xw33lCO 93u+tuW8+YmEGVsljD58jhmQn0LoIDVvW+NtIaWuXbS7IM12UfdpYKn1nEO/aYwhET WZpLj7Lgy45qi2a3DZhpsvPMziYsE+OmqghBfWBY= Date: Fri, 28 Jun 2019 13:34:51 -0700 From: Eric Biggers To: Jaskaran Singh 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: <20190628203450.GD103946@gmail.com> References: <20190619191048.20365-1-jaskarankhurana@linux.microsoft.com> <20190628040041.GB673@sol.localdomain> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: User-Agent: Mutt/1.10.1 (2018-07-13) Sender: linux-integrity-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-integrity@vger.kernel.org On Fri, Jun 28, 2019 at 12:45:11PM -0700, Jaskaran Singh Khurana wrote: > > Hello Eric, > On Thu, 27 Jun 2019, Eric Biggers wrote: > > > 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 > > > > In a datacenter like environment, this will protect the system from below > attacks: > > 1.Prevents attacker from deploying scripts that run arbitrary executables on the system. > 2.Prevents physically present malicious admin to run arbitrary code on the > machine. > > Regards, > Jaskaran So you are trying to protect against people who already have a root shell? Can't they just e.g. run /usr/bin/python and type in some Python code? Or run /usr/bin/curl and upload all your secret data to their server. - Eric