linux-kernel - Re: [PATCH v6 2/4] x86/modules: Increase randomization for modules

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Date:   Mon, 24 Sep 2018 14:29:54 -0700
From:   Kees Cook <keescook@...omium.org>
To:     "Edgecombe, Rick P" <rick.p.edgecombe@...el.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Matthew Wilcox <willy@...radead.org>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "daniel@...earbox.net" <daniel@...earbox.net>,
        "arjan@...ux.intel.com" <arjan@...ux.intel.com>,
        "jannh@...gle.com" <jannh@...gle.com>,
        "linux-mm@...ck.org" <linux-mm@...ck.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "kristen@...ux.intel.com" <kristen@...ux.intel.com>,
        "x86@...nel.org" <x86@...nel.org>, "hpa@...or.com" <hpa@...or.com>,
        "mingo@...hat.com" <mingo@...hat.com>,
        "alexei.starovoitov@...il.com" <alexei.starovoitov@...il.com>,
        "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>,
        "Hansen, Dave" <dave.hansen@...el.com>
Subject: Re: [PATCH v6 2/4] x86/modules: Increase randomization for modules

On Mon, Sep 24, 2018 at 2:27 PM, Edgecombe, Rick P
<rick.p.edgecombe@...el.com> wrote:
> On Mon, 2018-09-24 at 12:58 -0700, Kees Cook wrote:
>> On Mon, Sep 24, 2018 at 11:57 AM, Edgecombe, Rick P
>> <rick.p.edgecombe@...el.com> wrote:
>> > > Instead of having two open-coded __vmalloc_node_range() calls left in
>> > > this after the change, can this be done in terms of a call to
>> > > try_module_alloc() instead? I see they're slightly different, but it
>> > > might be nice for making the two paths share more code.
>> > Not sure what you mean. Across the whole change, there is one call
>> > to __vmalloc_node_range, and one to __vmalloc_node_try_addr.
>> I guess I meant the vmalloc calls -- one for node_range and one for
>> node_try_addr. I was wondering if the logic could be combined in some
>> way so that the __vmalloc_node_range() could be made in terms of the
>> the helper that try_module_randomize_each() uses. But this could just
>> be me hoping for nice-to-read changes. ;)
>>
>> -Kees
> One thing I had been considering was to move the whole "try random locations,
> then use backup" logic to vmalloc.c, and just have parameters for random area
> size, number of tries, etc. This way it could be possibly be re-used for other
> architectures for modules. Also on our list is to look at randomizing vmalloc
> space (especially stacks), which may or may not involve using a similar method.
>
> So maybe bit pre-mature refactoring, but would also clean up the code in
> module.c. Do you think it would be worth it?

I'd love to hear thoughts from -mm folks. Andrew, Matthew?

-Kees

-- 
Kees Cook
Pixel Security