ARM: poison memory between kuser helpers

Poison the memory between each kuser helper.  This ensures that any
branch between the kuser helpers will be appropriately trapped.

Cc: <stable@vger.kernel.org>
Acked-by: Nicolas Pitre <nico@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/kernel/entry-armv.S

@@ -742,6 +742,17 @@ ENDPROC(__switch_to)
 #endif
 	.endm
 
+	.macro	kuser_pad, sym, size
+	.if	(. - \sym) & 3
+	.rept	4 - (. - \sym) & 3
+	.byte	0
+	.endr
+	.endif
+	.rept	(\size - (. - \sym)) / 4
+	.word	0xe7fddef1
+	.endr
+	.endm
+
 	.align	5
 	.globl	__kuser_helper_start
 __kuser_helper_start:
@@ -832,18 +843,13 @@ kuser_cmpxchg64_fixup:
 #error "incoherent kernel configuration"
 #endif
 
-	/* pad to next slot */
-	.rept	(16 - (. - __kuser_cmpxchg64)/4)
-	.word	0
-	.endr
-
-	.align	5
+	kuser_pad __kuser_cmpxchg64, 64
 
 __kuser_memory_barrier:				@ 0xffff0fa0
 	smp_dmb	arm
 	usr_ret	lr
 
-	.align	5
+	kuser_pad __kuser_memory_barrier, 32
 
 __kuser_cmpxchg:				@ 0xffff0fc0
 
@@ -916,13 +922,14 @@ kuser_cmpxchg32_fixup:
 
 #endif
 
-	.align	5
+	kuser_pad __kuser_cmpxchg, 32
 
 __kuser_get_tls:				@ 0xffff0fe0
 	ldr	r0, [pc, #(16 - 8)]	@ read TLS, set in kuser_get_tls_init
 	usr_ret	lr
 	mrc	p15, 0, r0, c13, c0, 3	@ 0xffff0fe8 hardware TLS code
-	.rep	4
+	kuser_pad __kuser_get_tls, 16
+	.rep	3
 	.word	0			@ 0xffff0ff0 software TLS value, then
 	.endr				@ pad up to __kuser_helper_version