powerpc/kprobes: Use probe_address() to read instructions

In order to avoid Oopses, use probe_address() to read the
instruction at the address where the trap happened.
Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/7f24b5961a6839ff01df792816807f74ff236bf6.1582567319.git.christophe.leroy@c-s.fr

arch/powerpc/kernel/kprobes.c

@@ -287,14 +287,18 @@ int kprobe_handler(struct pt_regs *regs)
 
 	p = get_kprobe(addr);
 	if (!p) {
-		if (*addr != BREAKPOINT_INSTRUCTION) {
+		unsigned int instr;
+
+		if (probe_kernel_address(addr, instr))
+			goto no_kprobe;
+
+		if (instr != BREAKPOINT_INSTRUCTION) {
 			/*
 			 * PowerPC has multiple variants of the "trap"
 			 * instruction. If the current instruction is a
 			 * trap variant, it could belong to someone else
 			 */
-			kprobe_opcode_t cur_insn = *addr;
-			if (is_trap(cur_insn))
+			if (is_trap(instr))
 				goto no_kprobe;
 			/*
 			 * The breakpoint instruction was removed right