[PATCH 3.2 79/79] kaiser: Set _PAGE_NX only if supported

[Ben Hutchings]

3.2.99-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Lepton Wu <ytht.net@xxxxxxxxx>

This finally resolve crash if loaded under qemu + haxm. Haitao Shan pointed
out that the reason of that crash is that NX bit get set for page tables.
It seems we missed checking if _PAGE_NX is supported in kaiser_add_user_map

Link: https://www.spinics.net/lists/kernel/msg2689835.html

Reviewed-by: Guenter Roeck <groeck@xxxxxxxxxxxx>
Signed-off-by: Lepton Wu <ytht.net@xxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
(backported from Greg K-H's 4.4 stable-queue)
Signed-off-by: Juerg Haefliger <juerg.haefliger@xxxxxxxxxxxxx>
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
 arch/x86/mm/kaiser.c | 2 ++
 1 file changed, 2 insertions(+)

--- a/arch/x86/mm/kaiser.c
+++ b/arch/x86/mm/kaiser.c
@@ -189,6 +189,8 @@ static int kaiser_add_user_map(const voi
 	 * requires that not to be #defined to 0): so mask it off here.
 	 */
 	flags &= ~_PAGE_GLOBAL;
+	if (!(__supported_pte_mask & _PAGE_NX))
+		flags &= ~_PAGE_NX;
 
 	if (flags & _PAGE_USER)
 		BUG_ON(address < FIXADDR_START || end_addr >= FIXADDR_TOP);