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Message-ID: <20090904074626.GC20598@elte.hu>
Date: Fri, 4 Sep 2009 09:46:26 +0200
From: Ingo Molnar <mingo@...e.hu>
To: Siarhei Liakh <sliakh.lkml@...il.com>
Cc: linux-kernel@...r.kernel.org,
linux-security-module@...r.kernel.org,
Arjan van de Ven <arjan@...radead.org>,
James Morris <jmorris@...ei.org>,
Andrew Morton <akpm@...ux-foundation.org>,
Andi Kleen <ak@....de>, Rusty Russell <rusty@...tcorp.com.au>,
Thomas Gleixner <tglx@...utronix.de>,
"H. Peter Anvin" <hpa@...or.com>
Subject: Re: [PATCH V3] x86: NX protection for kernel data
* Siarhei Liakh <sliakh.lkml@...il.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@...il.com> and Xuxian Jiang <jiang@...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
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