linux-kernel - Re: [PATCH V2] x86: NX protection for kernel data

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Date:	Fri, 28 Aug 2009 16:52:22 +0800
From:	Amerigo Wang <xiyou.wangcong@...il.com>
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>, Ingo Molnar <mingo@...e.hu>
Subject: Re: [PATCH V2] x86: NX protection for kernel data

On Wed, Aug 26, 2009 at 01:20:19PM -0400, Siarhei Liakh 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 init/main.c with actual
>functionality: NX is set for all
>pages from _etext through _end.
>4. mark_nxdata_nx() called from init_post(void) in init/main.c (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>.
>


{snip}


>
> #include <linux/types.h>
>@@ -91,6 +93,21 @@ extern void radix_tree_init(void);
> extern void free_initmem(void);
> #ifndef CONFIG_DEBUG_RODATA
> static inline void mark_rodata_ro(void) { }
>+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);
>+}


I am afraid this function has to be in arch/x86/mm/init.c.
Seems set_pages_nx() is x86-specific.

Have you tested this on other arch?

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