[PATCH v9 2/8] powerpc/lib/code-patching: Set up Strict RWX patching earlier

[Russell Currey]

On Tue, 2021-03-16 at 14:17 +1100, Jordan Niethe wrote:
> setup_text_poke_area() is a late init call so it runs before
> mark_rodata_ro() and after the init calls. This lets all the init
> code
> patching simply write to their locations. In the future, kprobes is
> going to allocate its instruction pages RO which means they will need
> setup_text__poke_area() to have been already called for their code
> patching. However, init_kprobes() (which allocates and patches some
> instruction pages) is an early init call so it happens before
> setup_text__poke_area().
> 
> start_kernel() calls poking_init() before any of the init calls. On
> powerpc, poking_init() is currently a nop. setup_text_poke_area()
> relies
> on kernel virtual memory, cpu hotplug and per_cpu_areas being setup.
> setup_per_cpu_areas(), boot_cpu_hotplug_init() and mm_init() are
> called
> before poking_init().
> 
> Turn setup_text_poke_area() into poking_init().
> 
> Signed-off-by: Jordan Niethe <jniethe5 at gmail.com>

Good job finding & fixing this bug!

Reviewed-by: Russell Currey <ruscur at russell.cc>

> ---
> v9: New to series
> ---
>  arch/powerpc/lib/code-patching.c | 12 ++++--------
>  1 file changed, 4 insertions(+), 8 deletions(-)
> 
> diff --git a/arch/powerpc/lib/code-patching.c
> b/arch/powerpc/lib/code-patching.c
> index 2333625b5e31..b28afa1133db 100644
> --- a/arch/powerpc/lib/code-patching.c
> +++ b/arch/powerpc/lib/code-patching.c
> @@ -65,14 +65,11 @@ static int text_area_cpu_down(unsigned int cpu)
>  }
>  
>  /*
> - * Run as a late init call. This allows all the boot time patching
> to be done
> - * simply by patching the code, and then we're called here prior to
> - * mark_rodata_ro(), which happens after all init calls are run.
> Although
> - * BUG_ON() is rude, in this case it should only happen if ENOMEM,
> and we judge
> - * it as being preferable to a kernel that will crash later when
> someone tries
> - * to use patch_instruction().
> + * Although BUG_ON() is rude, in this case it should only happen if
> ENOMEM, and
> + * we judge it as being preferable to a kernel that will crash later
> when
> + * someone tries to use patch_instruction().
>   */
> -static int __init setup_text_poke_area(void)
> +int __init poking_init(void)
>  {
>         BUG_ON(!cpuhp_setup_state(CPUHP_AP_ONLINE_DYN,
>                 "powerpc/text_poke:online", text_area_cpu_up,
> @@ -80,7 +77,6 @@ static int __init setup_text_poke_area(void)
>  
>         return 0;
>  }
> -late_initcall(setup_text_poke_area);
>  
>  /*
>   * This can be called for kernel text or a module.