linux-kernel - [PATCH 1/6] x86: fix NX bit handling in change_page

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Date:	Fri, 25 Jan 2008 13:54:53 +0800
From:	"Huang, Ying" <ying.huang@...el.com>
To:	Ingo Molnar <mingo@...hat.com>, "H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>, Andi Kleen <ak@...e.de>
Cc:	linux-kernel@...r.kernel.org
Subject: [PATCH 1/6] x86: fix NX bit handling in change_page_attr

This patch fixes a bug of change_page_attr/change_page_attr_addr on
Intel i386/x86_64 CPUs.  After changing page attribute to be
executable with these functions, the page remains un-executable on
Intel i386/x86_64 CPU.  Because on Intel i386/x86_64 CPU, only if the
"NX" bits of all three level page tables are cleared (PAE is enabled),
the corresponding page is executable (refer to section 4.13.2 of Intel
64 and IA-32 Architectures Software Developer's Manual).  So, the bug
is fixed through clearing the "NX" bit of PMD when splitting the huge
PMD.

Signed-off-by: Huang Ying <ying.huang@...el.com>

---
 arch/x86/mm/pageattr.c |    1 +
 1 file changed, 1 insertion(+)

--- a/arch/x86/mm/pageattr.c
+++ b/arch/x86/mm/pageattr.c
@@ -124,6 +124,7 @@ static int split_large_page(pte_t *kpte,
 	/*
 	 * Install the new, split up pagetable:
 	 */
+	pgprot_val(ref_prot) &= ~_PAGE_NX;
 	__set_pmd_pte(kpte, address, mk_pte(base, ref_prot));
 	base = NULL;

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