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

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Date:   Fri, 26 May 2017 13:23:49 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     Kees Cook <keescook@...omium.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 1:17 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?