Re: [PATCH 1/4] task_struct: Allow randomized layout

[Kees Cook]

On Mon, Mar 26, 2018 at 5:03 AM, Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> On Mon, Mar 26, 2018 at 01:52:46PM +0200, Peter Zijlstra wrote:
>
>> That now looks like:
>>
>> struct task_struct {
>>         struct thread_info         thread_info;          /*     0    16 */
>>         volatile long int          state;                /*    16     8 */
>>
>>         /* XXX 40 bytes hole, try to pack */
>>
>>         /* --- cacheline 1 boundary (64 bytes) --- */
>>         struct {
>>                 void *             stack;                /*    64     8 */
>>                 atomic_t           usage;                /*    72     4 */
>>                 unsigned int       flags;                /*    76     4 */
>>                 unsigned int       ptrace;               /*    80     4 */
>>                 struct llist_node  wake_entry;           /*    88     8 */
>>
>>
>> Can we please undo this crap?
>
> The below gets rid of that nonsense.
>
> diff --git a/include/linux/compiler-gcc.h b/include/linux/compiler-gcc.h
> index e2c7f4369eff..767cf74d61f7 100644
> --- a/include/linux/compiler-gcc.h
> +++ b/include/linux/compiler-gcc.h
> @@ -242,6 +242,15 @@
>  #if defined(RANDSTRUCT_PLUGIN) && !defined(__CHECKER__)
>  #define __randomize_layout __attribute__((randomize_layout))
>  #define __no_randomize_layout __attribute__((no_randomize_layout))
> +/*
> + * RANDSTRUCT_PLUGIN wants to use an anonymous struct, but it is only
> + * possible since GCC 4.6. To provide as much build testing coverage
> + * as possible, this is used for all GCC 4.6+ builds, and not just on
> + * RANDSTRUCT_PLUGIN builds.
> + */
> +#define randomized_struct_fields_start struct {
> +#define randomized_struct_fields_end   } __randomize_layout;
> +
>  #endif
>
>  #endif /* GCC_VERSION >= 40500 */
> @@ -256,15 +265,6 @@
>   */
>  #define __visible      __attribute__((externally_visible))
>
> -/*
> - * RANDSTRUCT_PLUGIN wants to use an anonymous struct, but it is only
> - * possible since GCC 4.6. To provide as much build testing coverage
> - * as possible, this is used for all GCC 4.6+ builds, and not just on
> - * RANDSTRUCT_PLUGIN builds.
> - */
> -#define randomized_struct_fields_start struct {
> -#define randomized_struct_fields_end   } __randomize_layout;
> -
>  #endif /* GCC_VERSION >= 40600 */
>
>

This is fine by me, though obviously the comment would need to be updated. :)

-Kees

-- 
Kees Cook
Pixel Security