linux-kernel - Re: modules: add ro_after

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Date:	Thu, 21 Jul 2016 19:11:39 -0400
From:	Jessica Yu <jeyu@...hat.com>
To:	Kees Cook <keescook@...gle.com>
Cc:	Rusty Russell <rusty@...tcorp.com.au>,
	Linux API <linux-api@...r.kernel.org>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: modules: add ro_after_init support

+++ Kees Cook [21/07/16 16:03 -0700]:
>On Wed, Jun 29, 2016 at 9:56 PM, Rusty Russell <rusty@...tcorp.com.au> wrote:
>> Jessica Yu <jeyu@...hat.com> writes:
>>> +++ Rusty Russell [29/06/16 10:38 +0930]:
>>>>Jessica Yu <jeyu@...hat.com> writes:
>>>>> Add ro_after_init support for modules by adding a new page-aligned section
>>>>> in the module layout (after rodata) for ro_after_init data and enabling RO
>>>>> protection for that section after module init runs.
>>>>>
>>>>> Signed-off-by: Jessica Yu <jeyu@...hat.com>
>>>>
>>>>I would prefer a "bool after_init" flag to module_enable_ro().  It's
>>>>more explicit.
>>>
>>> Sure thing, I was just initially worried about the
>>> module_{enable,disable}_ro() asymmetry. :)
>>
>> Yes, but I think compile-time-analyzable behaviour beats
>> runtime-analyzable behaviour for clarity.
>>
>>>>Exposing the flags via uapi looks like a wart, but it's kind of a
>>>>feature, since we don't *unset* it in any section; userspace may want to
>>>>know about it.
>>>
>>> Hm, I'm still unsure about this. I'm starting to think it might be a
>>> bit overkill to expose SHF_RO_AFTER_INIT through uapi (although that
>>> is where all the other SHF_* flags are defined) SHF_RO_AFTER_INIT
>>> would technically be used only internally in the kernel (i.e. module
>>> loader), and it'd also be considered a non-standard flag, using a bit
>>> from SHF_MASKOS (OS-specific range). What do you think?
>>
>> Some arch *could* use it by setting the flag in a section in their
>> module I think; we don't stop them.  Since the other flags are there,
>> I'd leave it.
>>
>> We don't expose the flags via sysfs, though, so that's the only
>> exposure.
>
>What's the state of this series? I'd love it if the functionality
>could land for v4.8...
>

Hi Kees,

Sorry for the delay! Have been busier than usual lately. I'll be able
to get v2 out tomorrow.

Thanks!
Jessica