Re: [PATCH V3] x86: NX protection for kernel data

[Ingo Molnar <mingo@elte.hu>]

* Siarhei Liakh <sliakh.lkml@gmail.com> wrote:

> This patch expands functionality of CONFIG_DEBUG_RODATA to set main
> (static) kernel data area as NX.
> The following steps are taken to achieve this:
> 1. Linker script is adjusted so .text always starts and ends on a page boundary
> 2. Linker script is adjusted so .rodata and .data always start and
> end on a page boundary
> 3. void mark_nxdata_nx(void) added to arch/x86/mm/init.c with actual
> functionality: NX is set for all pages from _etext through _end.
> 4. mark_nxdata_nx() called from free_initmem() (after init has been released)
> 5. free_init_pages() sets released memory NX in arch/x86/mm/init.c
> 
> The patch have been developed for Linux 2.6.31-rc7 x86 by Siarhei Liakh
> <sliakh.lkml@gmail.com> and Xuxian Jiang <jiang@cs.ncsu.edu>.
> 
> V1:  initial patch for 2.6.30
> V2:  patch for 2.6.31-rc7
> V3:  moved all code into arch/x86, adjusted credits

ok, i like it.

One small cleanliness detail before we can apply it to the x86 tree:

> --- a/arch/x86/mm/init.c
> +++ b/arch/x86/mm/init.c
> @@ -440,11 +441,31 @@ void free_init_pages(char *what, unsigned long
> begin, unsigned long end)
>  #endif
>  }
> 
> +#ifndef CONFIG_DEBUG_RODATA
> +static inline void mark_nxdata_nx(void) { }
> +#else
> +void mark_nxdata_nx(void)
> +{
> +	/*
> +	 * When this called, init has already been executed and released,
> +	 * so everything past _etext sould be NX.
> +	 */
> +	unsigned long start = PFN_ALIGN(_etext);
> +	unsigned long size = PFN_ALIGN(_end) - start;
> +
> +	printk(KERN_INFO "NX-protecting the kernel data: %lx, %lu pages\n",
> +		start, size >> PAGE_SHIFT);
> +	set_pages_nx(virt_to_page(start), size >> PAGE_SHIFT);
> +}
> +#endif

This #ifdef looks ugly, it starts with an #ifndef which is inverted 
logic and mark_nxdata_nx() is a global symbol, needlessly. It should 
be written as something like:

static void mark_nxdata_nx(void)
{
#ifdef CONFIG_DEBUG_RODATA
...
#endif
}

Thanks,

	Ingo