ARM: 8772/1: kprobes: Prohibit kprobes on get_user functions

Since do_undefinstr() uses get_user to get the undefined
instruction, it can be called before kprobes processes
recursive check. This can cause an infinit recursive
exception.
Prohibit probing on get_user functions.

Fixes: 24ba613 ("ARM kprobes: core code")
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Cc: stable@vger.kernel.org
Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>

arch/arm/include/asm/assembler.h

@@ -536,4 +536,14 @@ THUMB(	orr	\reg , \reg , #PSR_T_BIT	)
 #endif
 	.endm
 
+#ifdef CONFIG_KPROBES
+#define _ASM_NOKPROBE(entry)				\
+	.pushsection "_kprobe_blacklist", "aw" ;	\
+	.balign 4 ;					\
+	.long entry;					\
+	.popsection
+#else
+#define _ASM_NOKPROBE(entry)
+#endif
+
 #endif /* __ASM_ASSEMBLER_H__ */

arch/arm/lib/getuser.S

@@ -38,6 +38,7 @@ ENTRY(__get_user_1)
 	mov	r0, #0
 	ret	lr
 ENDPROC(__get_user_1)
+_ASM_NOKPROBE(__get_user_1)
 
 ENTRY(__get_user_2)
 	check_uaccess r0, 2, r1, r2, __get_user_bad
@@ -58,13 +59,15 @@ rb	.req	r0
 	mov	r0, #0
 	ret	lr
 ENDPROC(__get_user_2)
+_ASM_NOKPROBE(__get_user_2)
 
 ENTRY(__get_user_4)
 	check_uaccess r0, 4, r1, r2, __get_user_bad
 4: TUSER(ldr)	r2, [r0]
 	mov	r0, #0
 	ret	lr
 ENDPROC(__get_user_4)
+_ASM_NOKPROBE(__get_user_4)
 
 ENTRY(__get_user_8)
 	check_uaccess r0, 8, r1, r2, __get_user_bad8
@@ -78,6 +81,7 @@ ENTRY(__get_user_8)
 	mov	r0, #0
 	ret	lr
 ENDPROC(__get_user_8)
+_ASM_NOKPROBE(__get_user_8)
 
 #ifdef __ARMEB__
 ENTRY(__get_user_32t_8)
@@ -91,13 +95,15 @@ ENTRY(__get_user_32t_8)
 	mov	r0, #0
 	ret	lr
 ENDPROC(__get_user_32t_8)
+_ASM_NOKPROBE(__get_user_32t_8)
 
 ENTRY(__get_user_64t_1)
 	check_uaccess r0, 1, r1, r2, __get_user_bad8
 8: TUSER(ldrb)	r3, [r0]
 	mov	r0, #0
 	ret	lr
 ENDPROC(__get_user_64t_1)
+_ASM_NOKPROBE(__get_user_64t_1)
 
 ENTRY(__get_user_64t_2)
 	check_uaccess r0, 2, r1, r2, __get_user_bad8
@@ -114,13 +120,15 @@ rb	.req	r0
 	mov	r0, #0
 	ret	lr
 ENDPROC(__get_user_64t_2)
+_ASM_NOKPROBE(__get_user_64t_2)
 
 ENTRY(__get_user_64t_4)
 	check_uaccess r0, 4, r1, r2, __get_user_bad8
 11: TUSER(ldr)	r3, [r0]
 	mov	r0, #0
 	ret	lr
 ENDPROC(__get_user_64t_4)
+_ASM_NOKPROBE(__get_user_64t_4)
 #endif
 
 __get_user_bad8:
@@ -131,6 +139,8 @@ __get_user_bad:
 	ret	lr
 ENDPROC(__get_user_bad)
 ENDPROC(__get_user_bad8)
+_ASM_NOKPROBE(__get_user_bad)
+_ASM_NOKPROBE(__get_user_bad8)
 
 .pushsection __ex_table, "a"
 	.long	1b, __get_user_bad