s390/kprobes: allow kprobes only on known instructions

Since we have an in-kernel disassembler we can make sure that
there won't be any kprobes set on random data.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/include/asm/dis.h

@@ -42,5 +42,11 @@ static inline int insn_length(unsigned char code)
 void show_code(struct pt_regs *regs);
 void print_fn_code(unsigned char *code, unsigned long len);
 int insn_to_mnemonic(unsigned char *instruction, char *buf, unsigned int len);
+struct s390_insn *find_insn(unsigned char *code);
+
+static inline int is_known_insn(unsigned char *code)
+{
+	return !!find_insn(code);
+}
 
 #endif /* __ASM_S390_DIS_H__ */

arch/s390/kernel/dis.c

@@ -1586,7 +1586,7 @@ static unsigned int extract_operand(unsigned char *code,
 	return val;
 }
 
-static struct s390_insn *find_insn(unsigned char *code)
+struct s390_insn *find_insn(unsigned char *code)
 {
 	unsigned char opfrag = code[1];
 	unsigned char opmask;

arch/s390/kernel/kprobes.c

@@ -60,6 +60,8 @@ struct kprobe_insn_cache kprobe_dmainsn_slots = {
 
 static int __kprobes is_prohibited_opcode(kprobe_opcode_t *insn)
 {
+	if (!is_known_insn((unsigned char *)insn))
+		return -EINVAL;
 	switch (insn[0] >> 8) {
 	case 0x0c:	/* bassm */
 	case 0x0b:	/* bsm	 */