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

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Message-ID: <87obki23uv.fsf@rustcorp.com.au>
Date:	Thu, 04 Oct 2012 15:09:04 +0930
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Kees Cook <keescook@...omium.org>, linux-kernel@...r.kernel.org
Cc:	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>,
	Kees Cook <keescook@...omium.org>,
	Jiri Kosina <jkosina@...e.cz>,
	linux-security-module@...r.kernel.org
Subject: Re: [PATCH 1/4] module: add syscall to load module from fd

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 :(

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

Thanks,
Rusty.
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