linux-kernel - Re: [PATCH v2] x86, mm: set NX across entire PMD at boot

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Date:	Sun, 16 Nov 2014 22:26:41 +0100 (CET)
From:	Thomas Gleixner <tglx@...utronix.de>
To:	Yinghai Lu <yinghai@...nel.org>
cc:	Kees Cook <keescook@...omium.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	the arch/x86 maintainers <x86@...nel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Andy Lutomirski <luto@...capital.net>,
	Yasuaki Ishimatsu <isimatu.yasuaki@...fujitsu.com>,
	Wang Nan <wangnan0@...wei.com>,
	David Vrabel <david.vrabel@...rix.com>
Subject: Re: [PATCH v2] x86, mm: set NX across entire PMD at boot

On Sat, 15 Nov 2014, Yinghai Lu wrote:
> +static pmd_t *last_pmd;
>  /*
>   * The head.S code sets up the kernel high mapping:
>   *
> @@ -408,9 +409,26 @@ void __init cleanup_highmap(void)
>              continue;
>          if (vaddr < (unsigned long) _text || vaddr > end)
>              set_pmd(pmd, __pmd(0));
> +        else
> +            last_pmd = pmd;

Why do you need to store this? You can compute this.
 
> +static void __init cleanup_highmap_tail(unsigned long addr)

Brilliant stuff. mark_rodata_ro() is called AFTER free_initmem() which
will free exactly that code.

> +{
> +    int i;
> +    pte_t *pte;
> +
> +    if (!last_pmd || pmd_none(*last_pmd))
> +        return;

Aside of the above: This is complete and utter crap. Just another
useless function which can be avoided by switching on brain before
coding.

> Index: linux-2.6/arch/x86/mm/pageattr.c
> ===================================================================
> --- linux-2.6.orig/arch/x86/mm/pageattr.c
> +++ linux-2.6/arch/x86/mm/pageattr.c
> @@ -100,7 +100,7 @@ static inline unsigned long highmap_star
> 
>  static inline unsigned long highmap_end_pfn(void)
>  {
> -    return __pa_symbol(roundup(_brk_end, PMD_SIZE)) >> PAGE_SHIFT;
> +    return __pa_symbol(PFN_ALIGN(_brk_end)) >> PAGE_SHIFT;
>  }

Wrong as well for CONFIG_DEBUG_RODATA=n for obvious reasons.

I know why I have your patches on blacklist ....

Thanks,

	tglx
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