Commit | Line | Data |
---|---|---|
f0907827 RV |
1 | /* SPDX-License-Identifier: GPL-2.0 OR MIT */ |
2 | #ifndef __LINUX_OVERFLOW_H | |
3 | #define __LINUX_OVERFLOW_H | |
4 | ||
5 | #include <linux/compiler.h> | |
a4947e84 | 6 | #include <linux/limits.h> |
230f6fa2 | 7 | #include <linux/const.h> |
f0907827 RV |
8 | |
9 | /* | |
4eb6bd55 ND |
10 | * We need to compute the minimum and maximum values representable in a given |
11 | * type. These macros may also be useful elsewhere. It would seem more obvious | |
12 | * to do something like: | |
f0907827 RV |
13 | * |
14 | * #define type_min(T) (T)(is_signed_type(T) ? (T)1 << (8*sizeof(T)-1) : 0) | |
15 | * #define type_max(T) (T)(is_signed_type(T) ? ((T)1 << (8*sizeof(T)-1)) - 1 : ~(T)0) | |
16 | * | |
17 | * Unfortunately, the middle expressions, strictly speaking, have | |
18 | * undefined behaviour, and at least some versions of gcc warn about | |
19 | * the type_max expression (but not if -fsanitize=undefined is in | |
20 | * effect; in that case, the warning is deferred to runtime...). | |
21 | * | |
22 | * The slightly excessive casting in type_min is to make sure the | |
23 | * macros also produce sensible values for the exotic type _Bool. [The | |
24 | * overflow checkers only almost work for _Bool, but that's | |
25 | * a-feature-not-a-bug, since people shouldn't be doing arithmetic on | |
26 | * _Bools. Besides, the gcc builtins don't allow _Bool* as third | |
27 | * argument.] | |
28 | * | |
29 | * Idea stolen from | |
30 | * https://mail-index.netbsd.org/tech-misc/2007/02/05/0000.html - | |
31 | * credit to Christian Biere. | |
32 | */ | |
f0907827 RV |
33 | #define __type_half_max(type) ((type)1 << (8*sizeof(type) - 1 - is_signed_type(type))) |
34 | #define type_max(T) ((T)((__type_half_max(T) - 1) + __type_half_max(T))) | |
35 | #define type_min(T) ((T)((T)-type_max(T)-(T)1)) | |
36 | ||
dc7fe518 LR |
37 | /* |
38 | * Avoids triggering -Wtype-limits compilation warning, | |
39 | * while using unsigned data types to check a < 0. | |
40 | */ | |
41 | #define is_non_negative(a) ((a) > 0 || (a) == 0) | |
42 | #define is_negative(a) (!(is_non_negative(a))) | |
f0907827 | 43 | |
9b80e4c4 KC |
44 | /* |
45 | * Allows for effectively applying __must_check to a macro so we can have | |
46 | * both the type-agnostic benefits of the macros while also being able to | |
47 | * enforce that the return value is, in fact, checked. | |
48 | */ | |
49 | static inline bool __must_check __must_check_overflow(bool overflow) | |
50 | { | |
51 | return unlikely(overflow); | |
52 | } | |
53 | ||
31970608 KC |
54 | /** |
55 | * check_add_overflow() - Calculate addition with overflow checking | |
d219d2a9 KC |
56 | * @a: first addend |
57 | * @b: second addend | |
58 | * @d: pointer to store sum | |
59 | * | |
60 | * Returns 0 on success. | |
61 | * | |
62 | * *@d holds the results of the attempted addition, but is not considered | |
63 | * "safe for use" on a non-zero return value, which indicates that the | |
64 | * sum has overflowed or been truncated. | |
f0907827 | 65 | */ |
d219d2a9 KC |
66 | #define check_add_overflow(a, b, d) \ |
67 | __must_check_overflow(__builtin_add_overflow(a, b, d)) | |
f0907827 | 68 | |
31970608 KC |
69 | /** |
70 | * check_sub_overflow() - Calculate subtraction with overflow checking | |
d219d2a9 KC |
71 | * @a: minuend; value to subtract from |
72 | * @b: subtrahend; value to subtract from @a | |
73 | * @d: pointer to store difference | |
74 | * | |
75 | * Returns 0 on success. | |
76 | * | |
77 | * *@d holds the results of the attempted subtraction, but is not considered | |
78 | * "safe for use" on a non-zero return value, which indicates that the | |
79 | * difference has underflowed or been truncated. | |
80 | */ | |
81 | #define check_sub_overflow(a, b, d) \ | |
82 | __must_check_overflow(__builtin_sub_overflow(a, b, d)) | |
f0907827 | 83 | |
31970608 KC |
84 | /** |
85 | * check_mul_overflow() - Calculate multiplication with overflow checking | |
d219d2a9 KC |
86 | * @a: first factor |
87 | * @b: second factor | |
88 | * @d: pointer to store product | |
89 | * | |
90 | * Returns 0 on success. | |
91 | * | |
92 | * *@d holds the results of the attempted multiplication, but is not | |
93 | * considered "safe for use" on a non-zero return value, which indicates | |
94 | * that the product has overflowed or been truncated. | |
95 | */ | |
96 | #define check_mul_overflow(a, b, d) \ | |
97 | __must_check_overflow(__builtin_mul_overflow(a, b, d)) | |
f0907827 | 98 | |
31970608 KC |
99 | /** |
100 | * check_shl_overflow() - Calculate a left-shifted value and check overflow | |
0c668477 JG |
101 | * @a: Value to be shifted |
102 | * @s: How many bits left to shift | |
103 | * @d: Pointer to where to store the result | |
104 | * | |
105 | * Computes *@d = (@a << @s) | |
106 | * | |
31970608 | 107 | * Returns true if '*@d' cannot hold the result or when '@a << @s' doesn't |
0c668477 | 108 | * make sense. Example conditions: |
0c668477 | 109 | * |
31970608 KC |
110 | * - '@a << @s' causes bits to be lost when stored in *@d. |
111 | * - '@s' is garbage (e.g. negative) or so large that the result of | |
112 | * '@a << @s' is guaranteed to be 0. | |
113 | * - '@a' is negative. | |
114 | * - '@a << @s' sets the sign bit, if any, in '*@d'. | |
115 | * | |
116 | * '*@d' will hold the results of the attempted shift, but is not | |
4578be13 | 117 | * considered "safe for use" if true is returned. |
0c668477 | 118 | */ |
9b80e4c4 | 119 | #define check_shl_overflow(a, s, d) __must_check_overflow(({ \ |
0c668477 JG |
120 | typeof(a) _a = a; \ |
121 | typeof(s) _s = s; \ | |
122 | typeof(d) _d = d; \ | |
123 | u64 _a_full = _a; \ | |
124 | unsigned int _to_shift = \ | |
dc7fe518 | 125 | is_non_negative(_s) && _s < 8 * sizeof(*d) ? _s : 0; \ |
0c668477 | 126 | *_d = (_a_full << _to_shift); \ |
dc7fe518 LR |
127 | (_to_shift != _s || is_negative(*_d) || is_negative(_a) || \ |
128 | (*_d >> _to_shift) != _a); \ | |
9b80e4c4 | 129 | })) |
0c668477 | 130 | |
4b21d25b KC |
131 | #define __overflows_type_constexpr(x, T) ( \ |
132 | is_unsigned_type(typeof(x)) ? \ | |
133 | (x) > type_max(typeof(T)) : \ | |
134 | is_unsigned_type(typeof(T)) ? \ | |
135 | (x) < 0 || (x) > type_max(typeof(T)) : \ | |
136 | (x) < type_min(typeof(T)) || (x) > type_max(typeof(T))) | |
137 | ||
138 | #define __overflows_type(x, T) ({ \ | |
139 | typeof(T) v = 0; \ | |
140 | check_add_overflow((x), v, &v); \ | |
141 | }) | |
142 | ||
143 | /** | |
144 | * overflows_type - helper for checking the overflows between value, variables, | |
145 | * or data type | |
146 | * | |
147 | * @n: source constant value or variable to be checked | |
148 | * @T: destination variable or data type proposed to store @x | |
149 | * | |
150 | * Compares the @x expression for whether or not it can safely fit in | |
151 | * the storage of the type in @T. @x and @T can have different types. | |
152 | * If @x is a constant expression, this will also resolve to a constant | |
153 | * expression. | |
154 | * | |
155 | * Returns: true if overflow can occur, false otherwise. | |
156 | */ | |
157 | #define overflows_type(n, T) \ | |
158 | __builtin_choose_expr(__is_constexpr(n), \ | |
159 | __overflows_type_constexpr(n, T), \ | |
160 | __overflows_type(n, T)) | |
161 | ||
162 | /** | |
163 | * castable_to_type - like __same_type(), but also allows for casted literals | |
164 | * | |
165 | * @n: variable or constant value | |
166 | * @T: variable or data type | |
167 | * | |
168 | * Unlike the __same_type() macro, this allows a constant value as the | |
169 | * first argument. If this value would not overflow into an assignment | |
170 | * of the second argument's type, it returns true. Otherwise, this falls | |
171 | * back to __same_type(). | |
172 | */ | |
173 | #define castable_to_type(n, T) \ | |
174 | __builtin_choose_expr(__is_constexpr(n), \ | |
175 | !__overflows_type_constexpr(n, T), \ | |
176 | __same_type(n, T)) | |
177 | ||
610b15c5 | 178 | /** |
e1be43d9 | 179 | * size_mul() - Calculate size_t multiplication with saturation at SIZE_MAX |
e1be43d9 KC |
180 | * @factor1: first factor |
181 | * @factor2: second factor | |
610b15c5 | 182 | * |
e1be43d9 KC |
183 | * Returns: calculate @factor1 * @factor2, both promoted to size_t, |
184 | * with any overflow causing the return value to be SIZE_MAX. The | |
185 | * lvalue must be size_t to avoid implicit type conversion. | |
610b15c5 | 186 | */ |
e1be43d9 | 187 | static inline size_t __must_check size_mul(size_t factor1, size_t factor2) |
610b15c5 KC |
188 | { |
189 | size_t bytes; | |
190 | ||
e1be43d9 | 191 | if (check_mul_overflow(factor1, factor2, &bytes)) |
610b15c5 KC |
192 | return SIZE_MAX; |
193 | ||
194 | return bytes; | |
195 | } | |
196 | ||
197 | /** | |
e1be43d9 | 198 | * size_add() - Calculate size_t addition with saturation at SIZE_MAX |
e1be43d9 KC |
199 | * @addend1: first addend |
200 | * @addend2: second addend | |
610b15c5 | 201 | * |
e1be43d9 KC |
202 | * Returns: calculate @addend1 + @addend2, both promoted to size_t, |
203 | * with any overflow causing the return value to be SIZE_MAX. The | |
204 | * lvalue must be size_t to avoid implicit type conversion. | |
610b15c5 | 205 | */ |
e1be43d9 | 206 | static inline size_t __must_check size_add(size_t addend1, size_t addend2) |
610b15c5 KC |
207 | { |
208 | size_t bytes; | |
209 | ||
e1be43d9 | 210 | if (check_add_overflow(addend1, addend2, &bytes)) |
610b15c5 KC |
211 | return SIZE_MAX; |
212 | ||
213 | return bytes; | |
214 | } | |
215 | ||
e1be43d9 KC |
216 | /** |
217 | * size_sub() - Calculate size_t subtraction with saturation at SIZE_MAX | |
e1be43d9 KC |
218 | * @minuend: value to subtract from |
219 | * @subtrahend: value to subtract from @minuend | |
220 | * | |
221 | * Returns: calculate @minuend - @subtrahend, both promoted to size_t, | |
222 | * with any overflow causing the return value to be SIZE_MAX. For | |
223 | * composition with the size_add() and size_mul() helpers, neither | |
224 | * argument may be SIZE_MAX (or the result with be forced to SIZE_MAX). | |
225 | * The lvalue must be size_t to avoid implicit type conversion. | |
e0478542 | 226 | */ |
e1be43d9 | 227 | static inline size_t __must_check size_sub(size_t minuend, size_t subtrahend) |
610b15c5 KC |
228 | { |
229 | size_t bytes; | |
230 | ||
e1be43d9 KC |
231 | if (minuend == SIZE_MAX || subtrahend == SIZE_MAX || |
232 | check_sub_overflow(minuend, subtrahend, &bytes)) | |
610b15c5 KC |
233 | return SIZE_MAX; |
234 | ||
235 | return bytes; | |
236 | } | |
237 | ||
238 | /** | |
e1be43d9 | 239 | * array_size() - Calculate size of 2-dimensional array. |
e1be43d9 KC |
240 | * @a: dimension one |
241 | * @b: dimension two | |
610b15c5 | 242 | * |
e1be43d9 KC |
243 | * Calculates size of 2-dimensional array: @a * @b. |
244 | * | |
245 | * Returns: number of bytes needed to represent the array or SIZE_MAX on | |
246 | * overflow. | |
610b15c5 | 247 | */ |
e1be43d9 KC |
248 | #define array_size(a, b) size_mul(a, b) |
249 | ||
250 | /** | |
251 | * array3_size() - Calculate size of 3-dimensional array. | |
e1be43d9 KC |
252 | * @a: dimension one |
253 | * @b: dimension two | |
254 | * @c: dimension three | |
255 | * | |
256 | * Calculates size of 3-dimensional array: @a * @b * @c. | |
257 | * | |
258 | * Returns: number of bytes needed to represent the array or SIZE_MAX on | |
259 | * overflow. | |
260 | */ | |
261 | #define array3_size(a, b, c) size_mul(size_mul(a, b), c) | |
610b15c5 | 262 | |
b19d57d0 GS |
263 | /** |
264 | * flex_array_size() - Calculate size of a flexible array member | |
265 | * within an enclosing structure. | |
b19d57d0 GS |
266 | * @p: Pointer to the structure. |
267 | * @member: Name of the flexible array member. | |
268 | * @count: Number of elements in the array. | |
269 | * | |
270 | * Calculates size of a flexible array of @count number of @member | |
271 | * elements, at the end of structure @p. | |
272 | * | |
273 | * Return: number of bytes needed or SIZE_MAX on overflow. | |
274 | */ | |
275 | #define flex_array_size(p, member, count) \ | |
230f6fa2 KC |
276 | __builtin_choose_expr(__is_constexpr(count), \ |
277 | (count) * sizeof(*(p)->member) + __must_be_array((p)->member), \ | |
278 | size_mul(count, sizeof(*(p)->member) + __must_be_array((p)->member))) | |
e1be43d9 KC |
279 | |
280 | /** | |
281 | * struct_size() - Calculate size of structure with trailing flexible array. | |
e1be43d9 KC |
282 | * @p: Pointer to the structure. |
283 | * @member: Name of the array member. | |
284 | * @count: Number of elements in the array. | |
285 | * | |
286 | * Calculates size of memory needed for structure @p followed by an | |
287 | * array of @count number of @member elements. | |
288 | * | |
289 | * Return: number of bytes needed or SIZE_MAX on overflow. | |
290 | */ | |
291 | #define struct_size(p, member, count) \ | |
230f6fa2 KC |
292 | __builtin_choose_expr(__is_constexpr(count), \ |
293 | sizeof(*(p)) + flex_array_size(p, member, count), \ | |
294 | size_add(sizeof(*(p)), flex_array_size(p, member, count))) | |
b19d57d0 | 295 | |
f0907827 | 296 | #endif /* __LINUX_OVERFLOW_H */ |