linux-kernel - Re: [PATCH 1/4] module: add syscall to load module from fd

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Message-ID: <CAGXu5j+i_6_2zUKZzFfptD53k+vQrgssw3r8qpn5WSQV1pnsyA@mail.gmail.com>
Date:	Thu, 4 Oct 2012 13:28:25 -0700
From:	Kees Cook <keescook@...omium.org>
To:	Rusty Russell <rusty@...tcorp.com.au>
Cc:	linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>,
	Mimi Zohar <zohar@...ux.vnet.ibm.com>,
	Serge Hallyn <serge.hallyn@...onical.com>,
	Arnd Bergmann <arnd@...db.de>,
	James Morris <james.l.morris@...cle.com>,
	Al Viro <viro@...iv.linux.org.uk>,
	Eric Paris <eparis@...hat.com>, Jiri Kosina <jkosina@...e.cz>,
	linux-security-module@...r.kernel.org
Subject: Re: [PATCH 1/4] module: add syscall to load module from fd

On Wed, Oct 3, 2012 at 10:39 PM, Rusty Russell <rusty@...tcorp.com.au> wrote:
> Kees Cook <keescook@...omium.org> writes:
>
>> On Thu, Sep 20, 2012 at 3:14 PM, Kees Cook <keescook@...omium.org> wrote:
>>> As part of the effort to create a stronger boundary between root and
>>> kernel, Chrome OS wants to be able to enforce that kernel modules are
>>> being loaded only from our read-only crypto-hash verified (dm_verity)
>>> root filesystem. Since the init_module syscall hands the kernel a module
>>> as a memory blob, no reasoning about the origin of the blob can be made.
>>>
>>> Earlier proposals for appending signatures to kernel modules would not be
>>> useful in Chrome OS, since it would involve adding an additional set of
>>> keys to our kernel and builds for no good reason: we already trust the
>>> contents of our root filesystem. We don't need to verify those kernel
>>> modules a second time. Having to do signature checking on module loading
>>> would slow us down and be redundant. All we need to know is where a
>>> module is coming from so we can say yes/no to loading it.
>>>
>>> If a file descriptor is used as the source of a kernel module, many more
>>> things can be reasoned about. In Chrome OS's case, we could enforce that
>>> the module lives on the filesystem we expect it to live on.  In the case
>>> of IMA (or other LSMs), it would be possible, for example, to examine
>>> extended attributes that may contain signatures over the contents of
>>> the module.
>>>
>>> This introduces a new syscall (on x86), similar to init_module, that has
>>> only two arguments. The first argument is used as a file descriptor to
>>> the module and the second argument is a pointer to the NULL terminated
>>> string of module arguments.
>>
>> Hi Rusty,
>>
>> Is this likely to land in the 3.7 change window? I'd really like to
>> get the syscall number assigned so I can start sending patches to
>> glibc, kmod, etc. My tree is here, FWIW:
>
> No, unfortunately it's a little late and there were issues with ARM
> signoffs and syscall numbers...
>
>> http://git.kernel.org/?p=linux/kernel/git/kees/linux.git;a=shortlog;h=refs/heads/module-fd-syscall
>
> Messy merge due to the module signing stuff going in :(

Sure was! :) I've done the merge now (and sent the v5 patches). I
think it looks pretty clean now.

> Please rebase on top of my kernel.org modules-next branch, and I'll pull
> into my modules-wip branch for 3.8.

As Mimi mentioned, it would be really nice if this could land in 3.7.
Can I maybe convince you? It's technically a small change, just with a
lot of reordering of the calling code, but I think it's a relatively
small change. The diff output is horrible due to extracting
do_init_module, but the code changed is pretty minimal.

-Kees

-- 
Kees Cook
Chrome OS Security
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