linux-kernel - Re: [PATCH 3/7] security: introduce kernel_fw_from

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Message-ID: <CAGXu5jLFQja7NGorKFrnMWHNW++YuyuX0MziOtZip91rbz0ovA@mail.gmail.com>
Date:	Tue, 22 Jul 2014 15:20:53 -0700
From:	Kees Cook <keescook@...omium.org>
To:	"Luis R. Rodriguez" <mcgrof@...e.com>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Ming Lei <ming.lei@...onical.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	James Morris <james.l.morris@...cle.com>,
	David Howells <dhowells@...hat.com>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	linux-security-module <linux-security-module@...r.kernel.org>,
	linux-firmware@...nel.org,
	linux-wireless <linux-wireless@...r.kernel.org>
Subject: Re: [PATCH 3/7] security: introduce kernel_fw_from_file hook

On Tue, Jul 22, 2014 at 3:11 PM, Luis R. Rodriguez <mcgrof@...e.com> wrote:
> On Tue, Jul 22, 2014 at 1:55 PM, Kees Cook <keescook@...omium.org> wrote:
>> On Tue, Jul 22, 2014 at 12:39 PM, Luis R. Rodriguez <mcgrof@...e.com> wrote:
>>> On Mon, Jul 14, 2014 at 3:31 PM, Kees Cook <keescook@...omium.org> wrote:
>>>> Yup, with this and the module hook, adding a similar hook for kexec
>>>> makes sense as well. A paranoid kernel doesn't want to trust anything
>>>> it's loading from userspace. :)
>>>
>>> Well I'm actually wondering if we could generalize requiring hooks or
>>> not for LSM as part of the general kobject definition. Then we
>>> wouldn't need to keep growing hooks for modules, firmware, kexec
>>> images, etc, but instead using the interfaces for kobjects and who
>>> depend on them. How that would actually look -- I'm not sure, but just
>>> a thought.
>>
>> Yeah, there does seem to be a repeated "get a thing from userspace"
>> method here, but the interfaces have been rather scattered so far. I
>> haven't seen an obvious way to consolidate them yet.
>
> If we are going to be adding a new system call for each type of
> userspace object to help LSMs with requirements I wonder if its a
> worthy endeavor to review. This series didn't add one but you had
> mentioned finit_module() for example, are we going to want one for
> finit_firmware() finit_kexec_image(), etc?

The kernel pulls in firmware directly from the filesystem, so no
syscall there. :) kexec just had kexec_load_file added as a syscall
(it takes 2 fds: kernel and initrd).

-Kees

-- 
Kees Cook
Chrome OS Security
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