linux-kernel - Re: [PATCH v8] RO/NX protection for loadable kernel modules

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Message-Id: <201002011209.13540.rusty@rustcorp.com.au>
Date:	Mon, 1 Feb 2010 12:09:13 +1030
From:	Rusty Russell <rusty@...tcorp.com.au>
To:	Siarhei Liakh <sliakh.lkml@...il.com>
Cc:	linux-kernel@...r.kernel.org,
	linux-security-module@...r.kernel.org, linux-next@...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>, Thomas Gleixner <tglx@...utronix.de>,
	"H. Peter Anvin" <hpa@...or.com>, Ingo Molnar <mingo@...e.hu>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	Dave Jones <davej@...hat.com>
Subject: Re: [PATCH v8] RO/NX protection for loadable kernel modules

On Mon, 1 Feb 2010 09:52:35 am Siarhei Liakh wrote:
> +/*
> + * Given BASE and SIZE this macro calculates the number of pages the
> + * memory regions occupies
> + */
> +#define NUMBER_OF_PAGES(BASE, SIZE) ((SIZE > 0) ?		\
> +		(PFN_DOWN((unsigned long)BASE + SIZE - 1) -	\
> +			 PFN_DOWN((unsigned long)BASE) + 1)	\
> +		: (0UL))

Needs more brackets around arguments, otherwise someone calling it with
a complex expression will get very upset.

Or just replace with a static inline function?

> +		if ((mod->module_core) && (mod->core_text_size > 0)) {

The core_text_size test should be enough here.

> +			begin_pfn = PFN_DOWN((unsigned long)mod->module_core);
> +			end_pfn = PFN_DOWN((unsigned long)mod->module_core +
> +						mod->core_text_size);
> +			if (end_pfn > begin_pfn)
> +				set_memory_rw(begin_pfn << PAGE_SHIFT,
> +							end_pfn - begin_pfn);

Much of this code might be neater if you created a helper:

	void set_page_attributes(void *start, void *end,
				 void (*set)(unsigned long start, unsigned long num_pages))
	{
		unsigned long begin_pfn = PFN_DOWN((unsigned long)start);
		unsigned long end_pfn = PFN_DOWN((unsigned long)end);
		if (end_pfn > begin_pfn)
			set(begin_pfn << PAGE_SHIFT, end_pfn - begin_pfn);
	}

But these are minor: patch looks good!

Thanks,
Rusty.
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