linux-kernel - Re: [PATCH 2/2] test: check copy_to/from

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Date:	Tue, 3 Dec 2013 14:03:22 -0800
From:	Kees Cook <keescook@...omium.org>
To:	Andrew Morton <akpm@...ux-foundation.org>
Cc:	LKML <linux-kernel@...r.kernel.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Ingo Molnar <mingo@...nel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	David Howells <dhowells@...hat.com>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCH 2/2] test: check copy_to/from_user boundary validation

On Tue, Dec 3, 2013 at 1:47 PM, Andrew Morton <akpm@...ux-foundation.org> wrote:
> On Tue,  3 Dec 2013 13:27:34 -0800 Kees Cook <keescook@...omium.org> wrote:
>
>> To help avoid an architecture failing to correctly check kernel/user
>> boundaries when handling copy_to_user, copy_from_user, put_user, or
>> get_user, perform some simple tests and fail to load if any of them
>> behave unexpectedly.
>>
>> Specifically, this is to make sure there is a way to notice if things
>> like what was fixed in 8404663f81d212918ff85f493649a7991209fa04 ("ARM:
>> 7527/1: uaccess: explicitly check __user pointer when !CPU_USE_DOMAINS")
>> ever regresses again, for any architecture.
>
> I guess the challenge will be to get anyone to remember to run this.

FWIW, I'll be running it. :) I'm sure Fengguang Wu could add it too.

> Really, this could be viewed as a candidate for
> tools/testing/selftests.  The tests in there are userspace tests, and
> your userspace test would consist of "modprobe test_user_copy".  The
> advantage of this is that your test will get included whenever someone
> runs the selftest suite.  This is better than having it stranded over
> in ./kernel/.

Sure, I'd be happy to add logic to that area too.

>> ---
>>  kernel/Makefile         |    1 +
>>  kernel/test_user_copy.c |  103 +++++++++++++++++++++++++++++++++++++++++++++++
>>  lib/Kconfig.debug       |   13 ++++++
>
> We already have a whole pile of test modules - seven of them reside in
> lib/ and I think there's an RCU one somewhere.  Can we bring order to
> all of this?  Some form of integration under tools/testing would be one
> approach.

I expect to be adding more of these, and I'd like to see these
collected in a single place as well. There are things like test_nx.c
in the x86 tree (which actually doesn't work any more, but that's a
separate issue).

> If you're disinclined to undertake such a project at this time, I'd
> suggest these two go into lib/ so they are known about if/when someone
> goes for the big cleanup.

lib/ sounds good. I'll move them there.

Thanks!

-Kees

-- 
Kees Cook
Chrome OS Security
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