1/*
2 * Copyright (C) 2012 Oracle.
3 *
4 * This program is free software; you can redistribute it and/or
5 * modify it under the terms of the GNU General Public License
6 * as published by the Free Software Foundation; either version 2
7 * of the License, or (at your option) any later version.
8 *
9 * This program is distributed in the hope that it will be useful,
10 * but WITHOUT ANY WARRANTY; without even the implied warranty of
11 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
12 * GNU General Public License for more details.
13 *
14 * You should have received a copy of the GNU General Public License
15 * along with this program; if not, see http://www.gnu.org/copyleft/gpl.txt
16 */
17
18#include "smatch.h"
19
20static int my_id;
21
22STATE(size_in_bytes);
23
24static void set_undefined(struct sm_state *sm, struct expression *mod_expr)
25{
26	if (sm->state == &size_in_bytes)
27		set_state(my_id, sm->name, sm->sym, &undefined);
28}
29
30static int is_sizeof(struct expression *expr)
31{
32	return (expr->type == EXPR_SIZEOF);
33}
34
35static int is_macro(struct expression *expr, const char *macro_name)
36{
37	char *name;
38	struct expression *outside_expr;
39
40	/* check that we aren't inside the macro itself */
41	outside_expr = last_ptr_list((struct ptr_list *)big_expression_stack);
42	if (outside_expr && positions_eq(expr->pos, outside_expr->pos))
43		return 0;
44
45	name = get_macro_name(expr->pos);
46	if (name && strcmp(name, macro_name) == 0)
47		return 1;
48	return 0;
49}
50
51static int is_size_in_bytes(struct expression *expr)
52{
53	if (is_sizeof(expr))
54		return 1;
55
56	if (is_macro(expr, "offsetof"))
57		return 1;
58	if (is_macro(expr, "PAGE_SIZE"))
59		return 1;
60
61	if (get_state_expr(my_id, expr) == &size_in_bytes)
62		return 1;
63
64	return 0;
65}
66
67static void match_binop(struct expression *expr)
68{
69	struct symbol *type;
70	char *name;
71	int size;
72
73	if (expr->op != '+')
74		return;
75	type = get_pointer_type(expr->left);
76	if (!type)
77		return;
78	if (type_bits(type) <= 8) /* ignore void, bool and char pointers*/
79		return;
80	if (!is_size_in_bytes(expr->right))
81		return;
82
83	/* if we know it's within bounds then don't complain */
84	size = get_array_size(expr->left);
85	if (size) {
86		sval_t max;
87
88		get_absolute_max(expr->right, &max);
89		if (max.uvalue < size)
90			return;
91	}
92
93	name = expr_to_str(expr->left);
94	sm_warning("potential pointer math issue ('%s' is a %d bit pointer)",
95	       name, type_bits(type));
96	free_string(name);
97}
98
99static void match_assign(struct expression *expr)
100{
101	if (expr->op != '=')
102		return;
103
104	if (!is_size_in_bytes(expr->right))
105		return;
106	set_state_expr(my_id, expr->left, &size_in_bytes);
107}
108
109static void check_assign(struct expression *expr)
110{
111	struct symbol *type;
112	char *name;
113
114	if (expr->op != SPECIAL_ADD_ASSIGN && expr->op != SPECIAL_SUB_ASSIGN)
115		return;
116
117	type = get_pointer_type(expr->left);
118	if (!type)
119		return;
120	if (type_bits(type) == 8 || type_bits(type) == -1)
121		return;
122	if (!is_size_in_bytes(expr->right))
123		return;
124	name = expr_to_var(expr->left);
125	sm_warning("potential pointer math issue ('%s' is a %d bit pointer)",
126	       name, type_bits(type));
127	free_string(name);
128}
129
130void check_pointer_math(int id)
131{
132	my_id = id;
133	add_hook(&match_binop, BINOP_HOOK);
134	add_hook(&match_assign, ASSIGNMENT_HOOK);
135	add_hook(&check_assign, ASSIGNMENT_HOOK);
136	add_modification_hook(my_id, &set_undefined);
137}
138