From mboxrd@z Thu Jan 1 00:00:00 1970 From: Mimi Zohar Subject: Re: [PATCH v2 0/3] initramfs: add support for xattrs in the initial ram disk Date: Mon, 13 May 2019 18:09:11 -0400 Message-ID: <1557785351.4969.94.camel@linux.ibm.com> References: <20190512194322.GA71658@rani.riverdale.lan> <3fe0e74b-19ca-6081-3afe-e05921b1bfe6@huawei.com> <4f522e28-29c8-5930-5d90-e0086b503613@landley.net> <20190513172007.GA69717@rani.riverdale.lan> <20190513175250.GC69717@rani.riverdale.lan> <1557772584.4969.62.camel@linux.ibm.com> <20190513184744.GA12386@rani.riverdale.lan> Mime-Version: 1.0 Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <20190513184744.GA12386@rani.riverdale.lan> Sender: linux-kernel-owner@vger.kernel.org To: Arvind Sankar Cc: Arvind Sankar , Roberto Sassu , Rob Landley , linux-kernel@vger.kernel.org, linux-api@vger.kernel.org, linux-fsdevel@vger.kernel.org, linux-integrity@vger.kernel.org, initramfs@vger.kernel.org List-Id: linux-api@vger.kernel.org On Mon, 2019-05-13 at 14:47 -0400, Arvind Sankar wrote: > On Mon, May 13, 2019 at 02:36:24PM -0400, Mimi Zohar wrote: > > > > > > How does this work today then? Is it actually the case that initramfs > > > > just cannot be used on an IMA-enabled system, or it can but it leaves > > > > the initramfs unverified and we're trying to fix that? I had assumed the > > > > latter. > > > Oooh, it's done not by starting IMA appraisal later, but by loading a > > > default policy to ignore initramfs? > > > > Right, when rootfs is a tmpfs filesystem, it supports xattrs, allowing > > for finer grained policies to be defined.  This patch set would allow > > a builtin IMA appraise policy to be defined which includes tmpfs. Clarification: finer grain IMA policy rules are normally defined in terms of LSM labels.  The LSMs need to enabled, before writing IMA policy rules in terms of the LSM labels. > > > Ok, but wouldn't my idea still work? Leave the default compiled-in > policy set to not appraise initramfs. The embedded /init sets all the > xattrs, changes the policy to appraise tmpfs, and then exec's the real > init? Then everything except the embedded /init and the file with the > xattrs will be appraised, and the embedded /init was verified as part of > the kernel image signature. The only additional kernel change needed > then is to add a config option to the kernel to disallow overwriting the > embedded initramfs (or at least the embedded /init). Yes and no.  The current IMA design allows a builtin policy to be specified on the boot command line ("ima_policy="), so that it exists from boot, and allows it to be replaced once with a custom policy.  After that, assuming that CONFIG_IMA_WRITE_POLICY is configured, additional rules may be appended.  As your embedded /init solution already replaces the builtin policy, the IMA policy couldn't currently be replaced a second time with a custom policy based on LSM labels. Mimi