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

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Date:	Thu, 12 Nov 2015 15:40:19 +0000
From:	Matt Fleming <matt@...eblueprint.co.uk>
To:	Ingo Molnar <mingo@...nel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	"H . Peter Anvin" <hpa@...or.com>
Cc:	Toshi Kani <toshi.kani@...com>,
	Matt Fleming <matt@...eblueprint.co.uk>,
	linux-kernel@...r.kernel.org, linux-efi@...r.kernel.org,
	Borislav Petkov <bp@...en8.de>,
	Sai Praneeth Prakhya <sai.praneeth.prakhya@...el.com>
Subject: [PATCH 2/6] x86/mm/pageattr: Do not strip pte flags from cpa->pfn

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;
-- 
2.6.2

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