kaiser: name that 0x1000 KAISER_SHADOW_PGD_OFFSET

There's a 0x1000 in various places, which looks better with a name.
Acked-by: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

CVE-2017-5754
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>

arch/x86/entry/entry_64.S

@@ -1292,7 +1292,7 @@ ENTRY(nmi)
 	movq	%cr3, %rax
 	pushq	%rax
 #ifdef CONFIG_KAISER_REAL_SWITCH
-	andq	$(~0x1000), %rax
+	andq	$(~KAISER_SHADOW_PGD_OFFSET), %rax
 #endif
 	movq	%rax, %cr3
 #endif
@@ -1535,7 +1535,7 @@ end_repeat_nmi:
 	movq	%cr3, %rax
 	pushq	%rax
 #ifdef CONFIG_KAISER_REAL_SWITCH
-	andq	$(~0x1000), %rax
+	andq	$(~KAISER_SHADOW_PGD_OFFSET), %rax
 #endif
 	movq	%rax, %cr3
 #endif

arch/x86/include/asm/kaiser.h

@@ -13,13 +13,16 @@
  * A minimalistic kernel mapping holds the parts needed to be mapped in user
  * mode, such as the entry/exit functions of the user space, or the stacks.
  */
+
+#define KAISER_SHADOW_PGD_OFFSET 0x1000
+
 #ifdef __ASSEMBLY__
 #ifdef CONFIG_KAISER
 
 .macro _SWITCH_TO_KERNEL_CR3 reg
 movq %cr3, \reg
 #ifdef CONFIG_KAISER_REAL_SWITCH
-andq $(~0x1000), \reg
+andq $(~KAISER_SHADOW_PGD_OFFSET), \reg
 #endif
 movq \reg, %cr3
 .endm
@@ -27,7 +30,7 @@ movq \reg, %cr3
 .macro _SWITCH_TO_USER_CR3 reg
 movq %cr3, \reg
 #ifdef CONFIG_KAISER_REAL_SWITCH
-orq $(0x1000), \reg
+orq $(KAISER_SHADOW_PGD_OFFSET), \reg
 #endif
 movq \reg, %cr3
 .endm