[PATCH v16 16/21] powerpc: Activate CONFIG_THREAD_INFO_IN_TASK

[Nicholas Piggin]

Michael Ellerman's on February 5, 2019 9:32 pm:
> From: Christophe Leroy <christophe.leroy at c-s.fr>
> 
> This patch activates CONFIG_THREAD_INFO_IN_TASK which
> moves the thread_info into task_struct.
> 
> Moving thread_info into task_struct has the following advantages:
>   - It protects thread_info from corruption in the case of stack
>     overflows.
>   - Its address is harder to determine if stack addresses are leaked,
>     making a number of attacks more difficult.
> 
> This has the following consequences:
>   - thread_info is now located at the beginning of task_struct.
>   - The 'cpu' field is now in task_struct, and only exists when
>     CONFIG_SMP is active.
>   - thread_info doesn't have anymore the 'task' field.
> 
> This patch:
>   - Removes all recopy of thread_info struct when the stack changes.
>   - Changes the CURRENT_THREAD_INFO() macro to point to current.
>   - Selects CONFIG_THREAD_INFO_IN_TASK.
>   - Modifies raw_smp_processor_id() to get ->cpu from current without
>     including linux/sched.h to avoid circular inclusion and without
>     including asm/asm-offsets.h to avoid symbol names duplication
>     between ASM constants and C constants.

Come to think of it, can this patch be split out entirely and moved
earlier as a 32-bit patch? 64-bit does not require that change or the 
additional build step AFAIKS?

Thanks,
Nick