linux-kernel - Re: [PATCH v2 19/20] [RFC] task_struct: Allow randomized layout

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Message-ID: <CAGXu5jJTrWzeLJkCELe0qNfMsoYfHbwL9sx-kBMm+4L8BatB7g@mail.gmail.com>
Date:   Fri, 26 May 2017 13:32:26 -0700
From:   Kees Cook <keescook@...omium.org>
To:     Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     "kernel-hardening@...ts.openwall.com" 
        <kernel-hardening@...ts.openwall.com>,
        Laura Abbott <labbott@...hat.com>,
        "the arch/x86 maintainers" <x86@...nel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 19/20] [RFC] task_struct: Allow randomized layout

On Fri, May 26, 2017 at 1:23 PM, Linus Torvalds
<torvalds@...ux-foundation.org> wrote:
> On Fri, May 26, 2017 at 1:17 PM, Kees Cook <keescook@...omium.org> wrote:
>> This marks most of the layout of task_struct as randomizable, but leaves
>> thread_info and scheduler state untouched at the start, and thread_struct
>> untouched at the end.
>
> I think you want to abstract this out somehow, because this is both
> ugly and bad:
>
>> +       /* This begins the randomizable portion of task_struct... */
>> +#if GCC_VERSION >= 40600
>> +       struct {
>> +#endif
>
> when you could instead just introduce something like
>
> #if GCC_VERSION >= 40600
>   #define randomized_struct_fields_start struct {
>   #define randomized_struct_fields_end } __randomize_layout;
> #else
>   #define randomized_struct_fields_start
>   #define randomized_struct_fields_end
> #endif
>
> and then this pattern is
>  (a) more-or-less self-documenting
>  (b) usable in other places too.
>  (c) maybe some future compiler wants that struct field to have some
> "randomize-me attribute" or something
>
> Hmm?

There were so many options and they all seems weird for various
reason. :) I'll use your idea, it looks much cleaner, thanks!

-Kees

-- 
Kees Cook
Pixel Security