linux-kernel - Re: [PATCH 2/6] x86/mm/pageattr: Do not strip pte flags from cpa->pfn

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Message-ID: <20151112184730.GI3838@pd.tnic>
Date:	Thu, 12 Nov 2015 19:47:30 +0100
From:	Borislav Petkov <bp@...en8.de>
To:	Matt Fleming <matt@...eblueprint.co.uk>
Cc:	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H . Peter Anvin" <hpa@...or.com>, Toshi Kani <toshi.kani@...com>,
	linux-kernel@...r.kernel.org, linux-efi@...r.kernel.org,
	Sai Praneeth Prakhya <sai.praneeth.prakhya@...el.com>
Subject: Re: [PATCH 2/6] x86/mm/pageattr: Do not strip pte flags from cpa->pfn

On Thu, Nov 12, 2015 at 03:40:19PM +0000, Matt Fleming wrote:
> Removing the PAGE_NX bit from cpa->pfn will corrupt the page frame
> number address rather than removing PAGE_NX as the code intends. This
> is unlikley to be a problem in practice because _PAGE_BIT_NX is bit 63
> and most machines do not have page frame numbers that reach that high.
> 
> Still, pte flags are never stored in cpa->pfn so we can safely delete
> the code.
> 
> Cc: Borislav Petkov <bp@...en8.de>
> Cc: Sai Praneeth Prakhya <sai.praneeth.prakhya@...el.com>
> Signed-off-by: Matt Fleming <matt@...eblueprint.co.uk>
> ---
>  arch/x86/mm/pageattr.c | 5 -----
>  1 file changed, 5 deletions(-)
> 
> diff --git a/arch/x86/mm/pageattr.c b/arch/x86/mm/pageattr.c
> index 893921b12272..d5240be55915 100644
> --- a/arch/x86/mm/pageattr.c
> +++ b/arch/x86/mm/pageattr.c
> @@ -885,11 +885,6 @@ static void populate_pte(struct cpa_data *cpa,
>  	pte = pte_offset_kernel(pmd, start);
>  
>  	while (num_pages-- && start < end) {
> -
> -		/* deal with the NX bit */
> -		if (!(pgprot_val(pgprot) & _PAGE_NX))
> -			cpa->pfn &= ~_PAGE_NX;
> -
>  		set_pte(pte, pfn_pte(cpa->pfn, pgprot));
>  
>  		start	 += PAGE_SIZE;
> -- 

I think this should be part of the 1st patch because there you're
correcting ->pfn to actually be a pfn.

-- 
Regards/Gruss,
    Boris.

ECO tip #101: Trim your mails when you reply.
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