uprobes/x86: Emulate relative conditional "near" jmp's

Change branch_setup_xol_ops() to simply use opc1 = OPCODE2(insn) - 0x10
if OPCODE1() == 0x0f; this matches the "short" jmp which checks the same
condition.

Thanks to lib/insn.c, it does the rest correctly. branch->ilen/offs are
correct no matter if this jmp is "near" or "short".
Reported-by: Jonathan Lebon <jlebon@redhat.com>
Signed-off-by: Oleg Nesterov <oleg@redhat.com>
Reviewed-by: Jim Keniston <jkenisto@us.ibm.com>

arch/x86/kernel/uprobes.c

@@ -599,6 +599,14 @@ static int branch_setup_xol_ops(struct arch_uprobe *auprobe, struct insn *insn)
 		branch_clear_offset(auprobe, insn);
 		break;
 
+	case 0x0f:
+		if (insn->opcode.nbytes != 2)
+			return -ENOSYS;
+		/*
+		 * If it is a "near" conditional jmp, OPCODE2() - 0x10 matches
+		 * OPCODE1() of the "short" jmp which checks the same condition.
+		 */
+		opc1 = OPCODE2(insn) - 0x10;
 	default:
 		if (!is_cond_jmp_opcode(opc1))
 			return -ENOSYS;