[PATCH 3.16 338/366] ARM: 8772/1: kprobes: Prohibit kprobes on get_user functions

[Ben Hutchings]

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

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

From: Masami Hiramatsu <mhiramat@xxxxxxxxxx>

commit 0d73c3f8e7f6ee2aab1bb350f60c180f5ae21a2c upstream.

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: 24ba613c9d6c ("ARM kprobes: core code")
Signed-off-by: Masami Hiramatsu <mhiramat@xxxxxxxxxx>
Signed-off-by: Russell King <rmk+kernel@xxxxxxxxxxxxxxx>
[bwh: Backported to 3.16: Drop changes to __get_user_{8,32_t_8,64t_{1,2,4}}]
Signed-off-by: Ben Hutchings <ben@xxxxxxxxxxxxxxx>
---
--- a/arch/arm/include/asm/assembler.h
+++ b/arch/arm/include/asm/assembler.h
@@ -425,4 +425,14 @@ 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__ */
--- a/arch/arm/lib/getuser.S
+++ b/arch/arm/lib/getuser.S
@@ -38,6 +38,7 @@ ENTRY(__get_user_1)
 	mov	r0, #0
 	mov	pc, lr
 ENDPROC(__get_user_1)
+_ASM_NOKPROBE(__get_user_1)
 
 ENTRY(__get_user_2)
 	check_uaccess r0, 2, r1, r2, __get_user_bad
@@ -58,6 +59,7 @@ rb	.req	r0
 	mov	r0, #0
 	mov	pc, lr
 ENDPROC(__get_user_2)
+_ASM_NOKPROBE(__get_user_2)
 
 ENTRY(__get_user_4)
 	check_uaccess r0, 4, r1, r2, __get_user_bad
@@ -65,12 +67,14 @@ ENTRY(__get_user_4)
 	mov	r0, #0
 	mov	pc, lr
 ENDPROC(__get_user_4)
+_ASM_NOKPROBE(__get_user_4)
 
 __get_user_bad:
 	mov	r2, #0
 	mov	r0, #-EFAULT
 	mov	pc, lr
 ENDPROC(__get_user_bad)
+_ASM_NOKPROBE(__get_user_bad)
 
 .pushsection __ex_table, "a"
 	.long	1b, __get_user_bad