[patch 21/29] x86: NX bit handling in change_page_attr()

[Greg Kroah-Hartman]

2.6.23-stable review patch.  If anyone has any objections, please let us
know.

------------------
From: Huang, Ying <ying.huang@xxxxxxxxx>

patch 84e0fdb1754d066dd0a8b257de7299f392d1e727 in mainline.

x86: NX bit handling in change_page_attr()

This patch fixes a bug of change_page_attr/change_page_attr_addr on
Intel x86_64 CPUs.  After changing page attribute to be executable with
these functions, the page remains un-executable on Intel x86_64 CPU.
Because on Intel x86_64 CPU, only if the "NX" bits of all four level
page tables are cleared, 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@xxxxxxxxx>
Cc: Andi Kleen <ak@xxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Ingo Molnar <mingo@xxxxxxx>
Signed-off-by: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 arch/x86_64/mm/pageattr.c |    1 +
 1 file changed, 1 insertion(+)

--- a/arch/x86_64/mm/pageattr.c
+++ b/arch/x86_64/mm/pageattr.c
@@ -148,6 +148,7 @@ __change_page_attr(unsigned long address
 			split = split_large_page(address, prot, ref_prot2);
 			if (!split)
 				return -ENOMEM;
+			pgprot_val(ref_prot2) &= ~_PAGE_NX;
 			set_pte(kpte, mk_pte(split, ref_prot2));
 			kpte_page = split;
 		}

-- 
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