[PATCH] arm64: mm: Mark .rodata as RO

[mark.rutland@arm.com (Mark Rutland)]

On Fri, Feb 12, 2016 at 10:13:19AM -0600, Jeremy Linton wrote:
> Currently the .rodata section is actually still executable when DEBUG_RODATA
> is enabled. This changes that so the .rodata is actually read only, no execute.
> 
> Signed-off-by: Jeremy Linton <jeremy.linton@arm.com>
> ---
>  arch/arm64/kernel/vmlinux.lds.S |  5 +++--
>  arch/arm64/mm/mmu.c             | 14 +++++++++++---
>  2 files changed, 14 insertions(+), 5 deletions(-)
> 
> diff --git a/arch/arm64/kernel/vmlinux.lds.S b/arch/arm64/kernel/vmlinux.lds.S
> index ab4e436..2e2c053 100644
> --- a/arch/arm64/kernel/vmlinux.lds.S
> +++ b/arch/arm64/kernel/vmlinux.lds.S
> @@ -114,8 +114,9 @@ SECTIONS
>  		*(.got)			/* Global offset table		*/
>  	}
>  
> -	RO_DATA(PAGE_SIZE)
> -	EXCEPTION_TABLE(8)
> +	ALIGN_DEBUG_RO_MIN(0)
> +	RO_DATA(PAGE_SIZE)		/* everything from this point to */
> +	EXCEPTION_TABLE(8)		/* _etext will be marked RO NX   */
>  	NOTES
>  
>  	ALIGN_DEBUG_RO_MIN(PAGE_SIZE)
> diff --git a/arch/arm64/mm/mmu.c b/arch/arm64/mm/mmu.c
> index ab69a99..a3f4112 100644
> --- a/arch/arm64/mm/mmu.c
> +++ b/arch/arm64/mm/mmu.c
> @@ -453,10 +453,18 @@ static void __init map_mem(pgd_t *pgd)
>  #ifdef CONFIG_DEBUG_RODATA
>  void mark_rodata_ro(void)
>  {
> -	create_mapping_late(__pa(_stext), (unsigned long)_stext,
> -				(unsigned long)_etext - (unsigned long)_stext,
> -				PAGE_KERNEL_ROX);
> +	unsigned long section_size;
>  
> +	section_size = (unsigned long)__start_rodata - (unsigned long)_stext;
> +	create_mapping_late(__pa(_stext), (unsigned long)_stext,
> +			    section_size, PAGE_KERNEL_ROX);
> +	/*
> +	 * mark .rodata as read only. Use _etext rather than __end_rodata to
> +	 * cover NOTES and EXCEPTION_TABLE.
> +	 */
> +	section_size = (unsigned long)_etext - (unsigned long)__start_rodata;
> +	create_mapping_late(__pa(__start_rodata), (unsigned long)__start_rodata,
> +			    section_size, PAGE_KERNEL_RO);
>  }

As you pointed out in the other thread, we'll also need to update
map_kernel to use equivalent chunks for .text and .rodata.

I think we can probably make .rodata RO from the outset in map_kernel,
too.

Could you please update mem_init to log .text and .rodata separately?

It looks like some core code makes assumptions about _etext, so I guess
that has to cover .rodata regardless.

Otherwise, looks good!

Thanks,
Mark.