ARM: kprobes: disallow probing stack consuming instructions

This patch prohibits probing instructions for which the stack
requirements are unable to be determined statically. Some test cases
are found not work again after the modification, this patch also
removes them.
Signed-off-by: Wang Nan <wangnan0@huawei.com>
Reviewed-by: Jon Medhurst <tixy@linaro.org>
Signed-off-by: Jon Medhurst <tixy@linaro.org>

arch/arm/include/asm/kprobes.h

@@ -22,7 +22,6 @@
 
 #define __ARCH_WANT_KPROBES_INSN_SLOT
 #define MAX_INSN_SIZE			2
-#define MAX_STACK_SIZE			64	/* 32 would probably be OK */
 
 #define flush_insn_slot(p)		do { } while (0)
 #define kretprobe_blacklist_size	0

arch/arm/include/asm/probes.h

@@ -19,6 +19,8 @@
 #ifndef _ASM_PROBES_H
 #define _ASM_PROBES_H
 
+#ifndef __ASSEMBLY__
+
 typedef u32 probes_opcode_t;
 
 struct arch_probes_insn;
@@ -41,4 +43,14 @@ struct arch_probes_insn {
 	int				stack_space;
 };
 
+#endif /* __ASSEMBLY__ */
+
+/*
+ * We assume one instruction can consume at most 64 bytes stack, which is
+ * 'push {r0-r15}'. Instructions consume more or unknown stack space like
+ * 'str r0, [sp, #-80]' and 'str r0, [sp, r1]' should be prohibit to probe.
+ * Both kprobe and jprobe use this macro.
+ */
+#define MAX_STACK_SIZE			64
+
 #endif

arch/arm/kernel/entry-armv.S

@@ -31,6 +31,7 @@
 
 #include "entry-header.S"
 #include <asm/entry-macro-multi.S>
+#include <asm/probes.h>
 
 /*
  * Interrupt handling.
@@ -249,7 +250,7 @@ __und_svc:
 	@ If a kprobe is about to simulate a "stmdb sp..." instruction,
 	@ it obviously needs free stack space which then will belong to
 	@ the saved context.
-	svc_entry 64
+	svc_entry MAX_STACK_SIZE
 #else
 	svc_entry
 #endif

arch/arm/probes/kprobes/core.c

@@ -115,6 +115,15 @@ int __kprobes arch_prepare_kprobe(struct kprobe *p)
 		break;
 	}
 
+	/*
+	 * Never instrument insn like 'str r0, [sp, +/-r1]'. Also, insn likes
+	 * 'str r0, [sp, #-68]' should also be prohibited.
+	 * See __und_svc.
+	 */
+	if ((p->ainsn.stack_space < 0) ||
+			(p->ainsn.stack_space > MAX_STACK_SIZE))
+		return -EINVAL;
+
 	return 0;
 }
 

arch/arm/probes/kprobes/test-arm.c

@@ -476,7 +476,8 @@ void kprobe_arm_test_cases(void)
 	TEST_GROUP("Extra load/store instructions")
 
 	TEST_RPR(  "strh	r",0, VAL1,", [r",1, 48,", -r",2, 24,"]")
-	TEST_RPR(  "streqh	r",14,VAL2,", [r",13,0, ", r",12, 48,"]")
+	TEST_RPR(  "streqh	r",14,VAL2,", [r",11,0, ", r",12, 48,"]")
+	TEST_UNSUPPORTED(  "streqh	r14, [r13, r12]")
 	TEST_RPR(  "strh	r",1, VAL1,", [r",2, 24,", r",3,  48,"]!")
 	TEST_RPR(  "strneh	r",12,VAL2,", [r",11,48,", -r",10,24,"]!")
 	TEST_RPR(  "strh	r",2, VAL1,", [r",3, 24,"], r",4, 48,"")
@@ -565,7 +566,8 @@ void kprobe_arm_test_cases(void)
 
 #if __LINUX_ARM_ARCH__ >= 5
 	TEST_RPR(  "strd	r",0, VAL1,", [r",1, 48,", -r",2,24,"]")
-	TEST_RPR(  "strccd	r",8, VAL2,", [r",13,0, ", r",12,48,"]")
+	TEST_RPR(  "strccd	r",8, VAL2,", [r",11,0, ", r",12,48,"]")
+	TEST_UNSUPPORTED(  "strccd r8, [r13, r12]")
 	TEST_RPR(  "strd	r",4, VAL1,", [r",2, 24,", r",3, 48,"]!")
 	TEST_RPR(  "strcsd	r",12,VAL2,", [r",11,48,", -r",10,24,"]!")
 	TEST_RPR(  "strd	r",2, VAL1,", [r",5, 24,"], r",4,48,"")
@@ -638,13 +640,15 @@ void kprobe_arm_test_cases(void)
 	TEST_RP( "str"byte"	r",2, VAL1,", [r",3, 24,"], #48")		\
 	TEST_RP( "str"byte"	r",10,VAL2,", [r",9, 64,"], #-48")		\
 	TEST_RPR("str"byte"	r",0, VAL1,", [r",1, 48,", -r",2, 24,"]")	\
-	TEST_RPR("str"byte"	r",14,VAL2,", [r",13,0, ", r",12, 48,"]")	\
+	TEST_RPR("str"byte"	r",14,VAL2,", [r",11,0, ", r",12, 48,"]")	\
+	TEST_UNSUPPORTED("str"byte" r14, [r13, r12]")	\
 	TEST_RPR("str"byte"	r",1, VAL1,", [r",2, 24,", r",3,  48,"]!")	\
 	TEST_RPR("str"byte"	r",12,VAL2,", [r",11,48,", -r",10,24,"]!")	\
 	TEST_RPR("str"byte"	r",2, VAL1,", [r",3, 24,"], r",4, 48,"")	\
 	TEST_RPR("str"byte"	r",10,VAL2,", [r",9, 48,"], -r",11,24,"")	\
 	TEST_RPR("str"byte"	r",0, VAL1,", [r",1, 24,", r",2,  32,", asl #1]")\
-	TEST_RPR("str"byte"	r",14,VAL2,", [r",13,0, ", r",12, 32,", lsr #2]")\
+	TEST_RPR("str"byte"	r",14,VAL2,", [r",11,0, ", r",12, 32,", lsr #2]")\
+	TEST_UNSUPPORTED("str"byte"	r14, [r13, r12, lsr #2]")\
 	TEST_RPR("str"byte"	r",1, VAL1,", [r",2, 24,", r",3,  32,", asr #3]!")\
 	TEST_RPR("str"byte"	r",12,VAL2,", [r",11,24,", r",10, 4,", ror #31]!")\
 	TEST_P(  "ldr"byte"	r0, [r",0,  24,", #-2]")			\
@@ -668,12 +672,12 @@ void kprobe_arm_test_cases(void)
 
 	LOAD_STORE("")
 	TEST_P(   "str	pc, [r",0,0,", #15*4]")
-	TEST_R(   "str	pc, [sp, r",2,15*4,"]")
+	TEST_UNSUPPORTED(   "str	pc, [sp, r2]")
 	TEST_BF(  "ldr	pc, [sp, #15*4]")
 	TEST_BF_R("ldr	pc, [sp, r",2,15*4,"]")
 
 	TEST_P(   "str	sp, [r",0,0,", #13*4]")
-	TEST_R(   "str	sp, [sp, r",2,13*4,"]")
+	TEST_UNSUPPORTED(   "str	sp, [sp, r2]")
 	TEST_BF(  "ldr	sp, [sp, #13*4]")
 	TEST_BF_R("ldr	sp, [sp, r",2,13*4,"]")