Re: [kernel-hardening] [RFC 2/7] init: add set_ro_mostly_after_init_rw/ro function

[Mark Rutland]

On Sun, Feb 19, 2017 at 07:04:05PM +0900, Hoeun Ryu wrote:
>  Add set_ro_mostly_after_init_rw/ro pair to modify memory attributes for
> memory marked as `ro_mostly_after_init`.
> 
>  I am doubtful that this is the right place where these functions reside and
> these functions are suitable for all architectures for memory attributes
> modification. Please comment.

These won't work for arm64, since set_memory_* only work on
page-granular mappings in the vmalloc area.

The "real" kernel mappings can use larger block mappings, and would need
to be split (which cannot be done at runtime) before permissions could
be changed at page granularity.

Thanks,
Mark.

> Signed-off-by: Hoeun Ryu <hoeun.ryu@xxxxxxxxx>
> ---
>  include/linux/init.h |  6 ++++++
>  init/main.c          | 24 ++++++++++++++++++++++++
>  2 files changed, 30 insertions(+)
> 
> diff --git a/include/linux/init.h b/include/linux/init.h
> index 79af096..d68e4f7 100644
> --- a/include/linux/init.h
> +++ b/include/linux/init.h
> @@ -131,6 +131,12 @@ extern bool rodata_enabled;
>  #endif
>  #ifdef CONFIG_STRICT_KERNEL_RWX
>  void mark_rodata_ro(void);
> +
> +void set_ro_mostly_after_init_rw(void);
> +void set_ro_mostly_after_init_ro(void);
> +#else
> +static inline void set_ro_mostly_after_init_rw(void) { }
> +static inline void set_ro_mostly_after_init_ro(void) { }
>  #endif
>  
>  extern void (*late_time_init)(void);
> diff --git a/init/main.c b/init/main.c
> index 4719abf..a5d4873 100644
> --- a/init/main.c
> +++ b/init/main.c
> @@ -941,6 +941,30 @@ static void mark_readonly(void)
>  	} else
>  		pr_info("Kernel memory protection disabled.\n");
>  }
> +
> +void set_ro_mostly_after_init_rw(void)
> +{
> +	unsigned long start = PFN_ALIGN(__start_data_ro_mostly_after_init);
> +	unsigned long end = PFN_ALIGN(&__end_data_ro_mostly_after_init);
> +	unsigned long nr_pages = (end - start) >> PAGE_SHIFT;
> +
> +	if (!rodata_enabled)
> +		return;
> +
> +	set_memory_rw(start, nr_pages);
> +}
> +
> +void set_ro_mostly_after_init_ro(void)
> +{
> +	unsigned long start = PFN_ALIGN(__start_data_ro_mostly_after_init);
> +	unsigned long end = PFN_ALIGN(&__end_data_ro_mostly_after_init);
> +	unsigned long nr_pages = (end - start) >> PAGE_SHIFT;
> +
> +	if (!rodata_enabled)
> +		return;
> +
> +	set_memory_ro(start, nr_pages);
> +}
>  #else
>  static inline void mark_readonly(void)
>  {
> -- 
> 2.7.4
>