From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751286AbeECVjI convert rfc822-to-8bit (ORCPT ); Thu, 3 May 2018 17:39:08 -0400 Received: from out01.mta.xmission.com ([166.70.13.231]:46412 "EHLO out01.mta.xmission.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751139AbeECVjG (ORCPT ); Thu, 3 May 2018 17:39:06 -0400 From: ebiederm@xmission.com (Eric W. Biederman) To: Mimi Zohar Cc: Kees Cook , David Howells , Matthew Garrett , linux-integrity@vger.kernel.org, linux-security-module@vger.kernel.org, kexec@lists.infradead.org, linux-kernel@vger.kernel.org, kernel-hardening@lists.openwall.com References: <1523572911-16363-1-git-send-email-zohar@linux.vnet.ibm.com> <87r2mso5up.fsf@xmission.com> <1525383075.3539.67.camel@linux.vnet.ibm.com> Date: Thu, 03 May 2018 16:38:57 -0500 In-Reply-To: <1525383075.3539.67.camel@linux.vnet.ibm.com> (Mimi Zohar's message of "Thu, 03 May 2018 17:31:15 -0400") Message-ID: <87d0yco1vy.fsf@xmission.com> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/25.1 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT X-XM-SPF: eid=1fELwO-0004TR-Co;;;mid=<87d0yco1vy.fsf@xmission.com>;;;hst=in02.mta.xmission.com;;;ip=97.119.174.25;;;frm=ebiederm@xmission.com;;;spf=neutral X-XM-AID: U2FsdGVkX1++UOxjXLvcp8fRHH8jwfJ5jZXTJVAA6Co= X-SA-Exim-Connect-IP: 97.119.174.25 X-SA-Exim-Mail-From: ebiederm@xmission.com X-Spam-Report: * -1.0 ALL_TRUSTED Passed through trusted hosts only via SMTP * 1.5 XMNoVowels Alpha-numberic number with no vowels * 0.0 T_TM2_M_HEADER_IN_MSG BODY: No description available. * 0.8 BAYES_50 BODY: Bayes spam probability is 40 to 60% * [score: 0.4978] * -0.0 DCC_CHECK_NEGATIVE Not listed in DCC * [sa06 1397; Body=1 Fuz1=1 Fuz2=1] * 1.0 T_XMDrugObfuBody_08 obfuscated drug references * 0.0 T_TooManySym_01 4+ unique symbols in subject X-Spam-DCC: XMission; sa06 1397; Body=1 Fuz1=1 Fuz2=1 X-Spam-Combo: **;Mimi Zohar X-Spam-Relay-Country: X-Spam-Timing: total 237 ms - load_scoreonly_sql: 0.03 (0.0%), signal_user_changed: 2.4 (1.0%), b_tie_ro: 1.70 (0.7%), parse: 0.84 (0.4%), extract_message_metadata: 3.3 (1.4%), get_uri_detail_list: 1.59 (0.7%), tests_pri_-1000: 3.6 (1.5%), tests_pri_-950: 1.19 (0.5%), tests_pri_-900: 0.99 (0.4%), tests_pri_-400: 23 (9.8%), check_bayes: 22 (9.4%), b_tokenize: 7 (2.9%), b_tok_get_all: 7 (3.1%), b_comp_prob: 2.6 (1.1%), b_tok_touch_all: 3.2 (1.3%), b_finish: 0.66 (0.3%), tests_pri_0: 190 (80.0%), check_dkim_signature: 0.71 (0.3%), check_dkim_adsp: 2.4 (1.0%), tests_pri_500: 4.6 (1.9%), rewrite_mail: 0.00 (0.0%) Subject: Re: [PATCH 0/3] kexec: limit kexec_load syscall X-Spam-Flag: No X-SA-Exim-Version: 4.2.1 (built Thu, 05 May 2016 13:38:54 -0600) X-SA-Exim-Scanned: Yes (on in02.mta.xmission.com) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Mimi Zohar writes: > [Cc'ing Kees and kernel-hardening] > > On Thu, 2018-05-03 at 15:13 -0500, Eric W. Biederman wrote: >> Mimi Zohar writes: >> >> > In environments that require the kexec kernel image to be signed, prevent >> > using the kexec_load syscall. In order for LSMs and IMA to differentiate >> > between kexec_load and kexec_file_load syscalls, this patch set adds a >> > call to security_kernel_read_file() in kexec_load_check(). >> >> Having thought about it some more this justification for these changes >> does not work. The functionality of kexec_load is already root-only. >> So in environments that require the kernel image to be signed just don't >> use kexec_load. Possibly even compile kexec_load out to save space >> because you will never need it. You don't need a new security hook to >> do any of that. Userspace is a very fine mechanism for being the >> instrument of policy. > > True, for those building their own kernel, they can disable the old > syscalls.  The concern is not for those building their own kernels, > but for those using stock kernels.   > > By adding an LSM hook here in the kexec_load syscall, as opposed to an > IMA specific hook, other LSMs can piggy back on top of it.  Currently, > both load_pin and SELinux are gating the kernel module syscalls based > on security_kernel_read_file. > > If there was a similar option for the kernel image, I'm pretty sure > other LSMs would use it. > > From an IMA perspective, there needs to be some method for only > allowing signed code to be loaded, executed, etc. - kernel modules, > kernel image/initramfs, firmware, policies. What is the IMA perspective. Why can't IMA trust appropriately authorized userspace? >> If you don't trust userspace that needs to be spelled out very clearly. >> You need to talk about what your threat models are. >> >> If the only justification is so that that we can't boot windows if >> someone hacks into userspace it has my nack because that is another kind >> of complete non-sense. > > The usecase is the ability to gate the kexec_load usage in stock > kernels. But kexec_load is already gated. It requires CAP_SYS_BOOT. >> Given that you are not trusting userspace this changeset also probably >> needs to have the kernel-hardening list cc'd. Because the only possible >> justification I can imagine for something like this is kernel-hardening. > > Sure, Cc'ing linux-hardening and Kees. > > Mimi