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21dcbebc | 1 | /* |
a28d06f3 | 2 | * Copyright 2014-2021 The OpenSSL Project Authors. All Rights Reserved. |
5a3d21c0 | 3 | * |
48f4ad77 | 4 | * Licensed under the Apache License 2.0 (the "License"). You may not use |
21dcbebc RS |
5 | * this file except in compliance with the License. You can obtain a copy |
6 | * in the file LICENSE in the source distribution or at | |
7 | * https://www.openssl.org/source/license.html | |
5a3d21c0 EK |
8 | */ |
9 | ||
ae4186b0 DMSP |
10 | #ifndef OSSL_INTERNAL_CONSTANT_TIME_H |
11 | # define OSSL_INTERNAL_CONSTANT_TIME_H | |
3a111aad | 12 | # pragma once |
5a3d21c0 | 13 | |
2688e7a0 | 14 | # include <stdlib.h> |
e0fa6324 | 15 | # include <string.h> |
80e0ecbf | 16 | # include <openssl/e_os2.h> /* For 'ossl_inline' */ |
5a3d21c0 | 17 | |
1d97c843 | 18 | /*- |
294d1e36 | 19 | * The boolean methods return a bitmask of all ones (0xff...f) for true |
5a3d21c0 EK |
20 | * and 0 for false. This is useful for choosing a value based on the result |
21 | * of a conditional in constant time. For example, | |
9018f3ce RS |
22 | * if (a < b) { |
23 | * c = a; | |
24 | * } else { | |
25 | * c = b; | |
26 | * } | |
5a3d21c0 | 27 | * can be written as |
9018f3ce RS |
28 | * unsigned int lt = constant_time_lt(a, b); |
29 | * c = constant_time_select(lt, a, b); | |
5a3d21c0 EK |
30 | */ |
31 | ||
b12169ee | 32 | /* Returns the given value with the MSB copied to all the other bits. */ |
80e0ecbf | 33 | static ossl_inline unsigned int constant_time_msb(unsigned int a); |
e0fa6324 MC |
34 | /* Convenience method for uint32_t. */ |
35 | static ossl_inline uint32_t constant_time_msb_32(uint32_t a); | |
9018f3ce RS |
36 | /* Convenience method for uint64_t. */ |
37 | static ossl_inline uint64_t constant_time_msb_64(uint64_t a); | |
5a3d21c0 | 38 | |
9018f3ce | 39 | /* Returns 0xff..f if a < b and 0 otherwise. */ |
80e0ecbf DSH |
40 | static ossl_inline unsigned int constant_time_lt(unsigned int a, |
41 | unsigned int b); | |
5a3d21c0 | 42 | /* Convenience method for getting an 8-bit mask. */ |
80e0ecbf DSH |
43 | static ossl_inline unsigned char constant_time_lt_8(unsigned int a, |
44 | unsigned int b); | |
9018f3ce RS |
45 | /* Convenience method for uint64_t. */ |
46 | static ossl_inline uint64_t constant_time_lt_64(uint64_t a, uint64_t b); | |
5a3d21c0 | 47 | |
9018f3ce | 48 | /* Returns 0xff..f if a >= b and 0 otherwise. */ |
80e0ecbf DSH |
49 | static ossl_inline unsigned int constant_time_ge(unsigned int a, |
50 | unsigned int b); | |
5a3d21c0 | 51 | /* Convenience method for getting an 8-bit mask. */ |
80e0ecbf DSH |
52 | static ossl_inline unsigned char constant_time_ge_8(unsigned int a, |
53 | unsigned int b); | |
5a3d21c0 | 54 | |
9018f3ce | 55 | /* Returns 0xff..f if a == 0 and 0 otherwise. */ |
80e0ecbf | 56 | static ossl_inline unsigned int constant_time_is_zero(unsigned int a); |
5a3d21c0 | 57 | /* Convenience method for getting an 8-bit mask. */ |
80e0ecbf | 58 | static ossl_inline unsigned char constant_time_is_zero_8(unsigned int a); |
e0fa6324 MC |
59 | /* Convenience method for getting a 32-bit mask. */ |
60 | static ossl_inline uint32_t constant_time_is_zero_32(uint32_t a); | |
5a3d21c0 | 61 | |
9018f3ce | 62 | /* Returns 0xff..f if a == b and 0 otherwise. */ |
80e0ecbf DSH |
63 | static ossl_inline unsigned int constant_time_eq(unsigned int a, |
64 | unsigned int b); | |
5a3d21c0 | 65 | /* Convenience method for getting an 8-bit mask. */ |
80e0ecbf DSH |
66 | static ossl_inline unsigned char constant_time_eq_8(unsigned int a, |
67 | unsigned int b); | |
455b65df | 68 | /* Signed integers. */ |
80e0ecbf | 69 | static ossl_inline unsigned int constant_time_eq_int(int a, int b); |
455b65df | 70 | /* Convenience method for getting an 8-bit mask. */ |
80e0ecbf | 71 | static ossl_inline unsigned char constant_time_eq_int_8(int a, int b); |
455b65df | 72 | |
1d97c843 | 73 | /*- |
294d1e36 EK |
74 | * Returns (mask & a) | (~mask & b). |
75 | * | |
76 | * When |mask| is all 1s or all 0s (as returned by the methods above), | |
77 | * the select methods return either |a| (if |mask| is nonzero) or |b| | |
78 | * (if |mask| is zero). | |
79 | */ | |
80e0ecbf DSH |
80 | static ossl_inline unsigned int constant_time_select(unsigned int mask, |
81 | unsigned int a, | |
82 | unsigned int b); | |
294d1e36 | 83 | /* Convenience method for unsigned chars. */ |
80e0ecbf DSH |
84 | static ossl_inline unsigned char constant_time_select_8(unsigned char mask, |
85 | unsigned char a, | |
86 | unsigned char b); | |
e0fa6324 MC |
87 | |
88 | /* Convenience method for uint32_t. */ | |
89 | static ossl_inline uint32_t constant_time_select_32(uint32_t mask, uint32_t a, | |
90 | uint32_t b); | |
91 | ||
9018f3ce RS |
92 | /* Convenience method for uint64_t. */ |
93 | static ossl_inline uint64_t constant_time_select_64(uint64_t mask, uint64_t a, | |
94 | uint64_t b); | |
294d1e36 | 95 | /* Convenience method for signed integers. */ |
80e0ecbf DSH |
96 | static ossl_inline int constant_time_select_int(unsigned int mask, int a, |
97 | int b); | |
294d1e36 | 98 | |
9018f3ce | 99 | |
80e0ecbf | 100 | static ossl_inline unsigned int constant_time_msb(unsigned int a) |
0f113f3e MC |
101 | { |
102 | return 0 - (a >> (sizeof(a) * 8 - 1)); | |
103 | } | |
5a3d21c0 | 104 | |
e0fa6324 MC |
105 | |
106 | static ossl_inline uint32_t constant_time_msb_32(uint32_t a) | |
107 | { | |
108 | return 0 - (a >> 31); | |
109 | } | |
110 | ||
9018f3ce RS |
111 | static ossl_inline uint64_t constant_time_msb_64(uint64_t a) |
112 | { | |
113 | return 0 - (a >> 63); | |
114 | } | |
115 | ||
2688e7a0 MC |
116 | static ossl_inline size_t constant_time_msb_s(size_t a) |
117 | { | |
118 | return 0 - (a >> (sizeof(a) * 8 - 1)); | |
119 | } | |
120 | ||
80e0ecbf DSH |
121 | static ossl_inline unsigned int constant_time_lt(unsigned int a, |
122 | unsigned int b) | |
0f113f3e MC |
123 | { |
124 | return constant_time_msb(a ^ ((a ^ b) | ((a - b) ^ b))); | |
125 | } | |
5a3d21c0 | 126 | |
2688e7a0 MC |
127 | static ossl_inline size_t constant_time_lt_s(size_t a, size_t b) |
128 | { | |
129 | return constant_time_msb_s(a ^ ((a ^ b) | ((a - b) ^ b))); | |
130 | } | |
131 | ||
80e0ecbf DSH |
132 | static ossl_inline unsigned char constant_time_lt_8(unsigned int a, |
133 | unsigned int b) | |
0f113f3e | 134 | { |
26a7d938 | 135 | return (unsigned char)constant_time_lt(a, b); |
0f113f3e | 136 | } |
5a3d21c0 | 137 | |
9018f3ce RS |
138 | static ossl_inline uint64_t constant_time_lt_64(uint64_t a, uint64_t b) |
139 | { | |
140 | return constant_time_msb_64(a ^ ((a ^ b) | ((a - b) ^ b))); | |
141 | } | |
142 | ||
80e0ecbf DSH |
143 | static ossl_inline unsigned int constant_time_ge(unsigned int a, |
144 | unsigned int b) | |
0f113f3e MC |
145 | { |
146 | return ~constant_time_lt(a, b); | |
147 | } | |
5a3d21c0 | 148 | |
2688e7a0 MC |
149 | static ossl_inline size_t constant_time_ge_s(size_t a, size_t b) |
150 | { | |
151 | return ~constant_time_lt_s(a, b); | |
152 | } | |
153 | ||
80e0ecbf DSH |
154 | static ossl_inline unsigned char constant_time_ge_8(unsigned int a, |
155 | unsigned int b) | |
0f113f3e | 156 | { |
26a7d938 | 157 | return (unsigned char)constant_time_ge(a, b); |
0f113f3e | 158 | } |
5a3d21c0 | 159 | |
2688e7a0 MC |
160 | static ossl_inline unsigned char constant_time_ge_8_s(size_t a, size_t b) |
161 | { | |
26a7d938 | 162 | return (unsigned char)constant_time_ge_s(a, b); |
2688e7a0 MC |
163 | } |
164 | ||
80e0ecbf | 165 | static ossl_inline unsigned int constant_time_is_zero(unsigned int a) |
0f113f3e MC |
166 | { |
167 | return constant_time_msb(~a & (a - 1)); | |
168 | } | |
5a3d21c0 | 169 | |
2688e7a0 MC |
170 | static ossl_inline size_t constant_time_is_zero_s(size_t a) |
171 | { | |
172 | return constant_time_msb_s(~a & (a - 1)); | |
173 | } | |
174 | ||
80e0ecbf | 175 | static ossl_inline unsigned char constant_time_is_zero_8(unsigned int a) |
0f113f3e | 176 | { |
26a7d938 | 177 | return (unsigned char)constant_time_is_zero(a); |
0f113f3e | 178 | } |
5a3d21c0 | 179 | |
e0fa6324 MC |
180 | static ossl_inline uint32_t constant_time_is_zero_32(uint32_t a) |
181 | { | |
182 | return constant_time_msb_32(~a & (a - 1)); | |
183 | } | |
184 | ||
80e0ecbf DSH |
185 | static ossl_inline unsigned int constant_time_eq(unsigned int a, |
186 | unsigned int b) | |
0f113f3e MC |
187 | { |
188 | return constant_time_is_zero(a ^ b); | |
189 | } | |
5a3d21c0 | 190 | |
2688e7a0 MC |
191 | static ossl_inline size_t constant_time_eq_s(size_t a, size_t b) |
192 | { | |
193 | return constant_time_is_zero_s(a ^ b); | |
194 | } | |
195 | ||
80e0ecbf DSH |
196 | static ossl_inline unsigned char constant_time_eq_8(unsigned int a, |
197 | unsigned int b) | |
0f113f3e | 198 | { |
26a7d938 | 199 | return (unsigned char)constant_time_eq(a, b); |
0f113f3e | 200 | } |
5a3d21c0 | 201 | |
2688e7a0 MC |
202 | static ossl_inline unsigned char constant_time_eq_8_s(size_t a, size_t b) |
203 | { | |
26a7d938 | 204 | return (unsigned char)constant_time_eq_s(a, b); |
2688e7a0 MC |
205 | } |
206 | ||
80e0ecbf | 207 | static ossl_inline unsigned int constant_time_eq_int(int a, int b) |
0f113f3e MC |
208 | { |
209 | return constant_time_eq((unsigned)(a), (unsigned)(b)); | |
210 | } | |
455b65df | 211 | |
80e0ecbf | 212 | static ossl_inline unsigned char constant_time_eq_int_8(int a, int b) |
0f113f3e MC |
213 | { |
214 | return constant_time_eq_8((unsigned)(a), (unsigned)(b)); | |
215 | } | |
455b65df | 216 | |
04edd688 BE |
217 | /* |
218 | * Returns the value unmodified, but avoids optimizations. | |
219 | * The barriers prevent the compiler from narrowing down the | |
220 | * possible value range of the mask and ~mask in the select | |
221 | * statements, which avoids the recognition of the select | |
222 | * and turning it into a conditional load or branch. | |
223 | */ | |
224 | static ossl_inline unsigned int value_barrier(unsigned int a) | |
225 | { | |
226 | #if !defined(OPENSSL_NO_ASM) && defined(__GNUC__) | |
227 | unsigned int r; | |
228 | __asm__("" : "=r"(r) : "0"(a)); | |
229 | #else | |
230 | volatile unsigned int r = a; | |
231 | #endif | |
232 | return r; | |
233 | } | |
234 | ||
235 | /* Convenience method for uint32_t. */ | |
236 | static ossl_inline uint32_t value_barrier_32(uint32_t a) | |
237 | { | |
238 | #if !defined(OPENSSL_NO_ASM) && defined(__GNUC__) | |
239 | uint32_t r; | |
240 | __asm__("" : "=r"(r) : "0"(a)); | |
241 | #else | |
242 | volatile uint32_t r = a; | |
243 | #endif | |
244 | return r; | |
245 | } | |
246 | ||
247 | /* Convenience method for uint64_t. */ | |
248 | static ossl_inline uint64_t value_barrier_64(uint64_t a) | |
249 | { | |
250 | #if !defined(OPENSSL_NO_ASM) && defined(__GNUC__) | |
251 | uint64_t r; | |
252 | __asm__("" : "=r"(r) : "0"(a)); | |
253 | #else | |
254 | volatile uint64_t r = a; | |
255 | #endif | |
256 | return r; | |
257 | } | |
258 | ||
259 | /* Convenience method for size_t. */ | |
260 | static ossl_inline size_t value_barrier_s(size_t a) | |
261 | { | |
262 | #if !defined(OPENSSL_NO_ASM) && defined(__GNUC__) | |
263 | size_t r; | |
264 | __asm__("" : "=r"(r) : "0"(a)); | |
265 | #else | |
266 | volatile size_t r = a; | |
267 | #endif | |
268 | return r; | |
269 | } | |
270 | ||
80e0ecbf DSH |
271 | static ossl_inline unsigned int constant_time_select(unsigned int mask, |
272 | unsigned int a, | |
273 | unsigned int b) | |
0f113f3e | 274 | { |
04edd688 | 275 | return (value_barrier(mask) & a) | (value_barrier(~mask) & b); |
0f113f3e | 276 | } |
294d1e36 | 277 | |
2688e7a0 MC |
278 | static ossl_inline size_t constant_time_select_s(size_t mask, |
279 | size_t a, | |
280 | size_t b) | |
281 | { | |
04edd688 | 282 | return (value_barrier_s(mask) & a) | (value_barrier_s(~mask) & b); |
2688e7a0 MC |
283 | } |
284 | ||
80e0ecbf DSH |
285 | static ossl_inline unsigned char constant_time_select_8(unsigned char mask, |
286 | unsigned char a, | |
287 | unsigned char b) | |
0f113f3e | 288 | { |
26a7d938 | 289 | return (unsigned char)constant_time_select(mask, a, b); |
0f113f3e | 290 | } |
294d1e36 | 291 | |
80e0ecbf DSH |
292 | static ossl_inline int constant_time_select_int(unsigned int mask, int a, |
293 | int b) | |
0f113f3e | 294 | { |
26a7d938 | 295 | return (int)constant_time_select(mask, (unsigned)(a), (unsigned)(b)); |
0f113f3e | 296 | } |
294d1e36 | 297 | |
2688e7a0 MC |
298 | static ossl_inline int constant_time_select_int_s(size_t mask, int a, int b) |
299 | { | |
26a7d938 K |
300 | return (int)constant_time_select((unsigned)mask, (unsigned)(a), |
301 | (unsigned)(b)); | |
2688e7a0 MC |
302 | } |
303 | ||
e0fa6324 MC |
304 | static ossl_inline uint32_t constant_time_select_32(uint32_t mask, uint32_t a, |
305 | uint32_t b) | |
306 | { | |
04edd688 | 307 | return (value_barrier_32(mask) & a) | (value_barrier_32(~mask) & b); |
e0fa6324 MC |
308 | } |
309 | ||
9018f3ce RS |
310 | static ossl_inline uint64_t constant_time_select_64(uint64_t mask, uint64_t a, |
311 | uint64_t b) | |
312 | { | |
04edd688 | 313 | return (value_barrier_64(mask) & a) | (value_barrier_64(~mask) & b); |
9018f3ce RS |
314 | } |
315 | ||
e0fa6324 MC |
316 | /* |
317 | * mask must be 0xFFFFFFFF or 0x00000000. | |
318 | * | |
319 | * if (mask) { | |
320 | * uint32_t tmp = *a; | |
321 | * | |
322 | * *a = *b; | |
323 | * *b = tmp; | |
324 | * } | |
325 | */ | |
326 | static ossl_inline void constant_time_cond_swap_32(uint32_t mask, uint32_t *a, | |
327 | uint32_t *b) | |
328 | { | |
329 | uint32_t xor = *a ^ *b; | |
330 | ||
331 | xor &= mask; | |
332 | *a ^= xor; | |
333 | *b ^= xor; | |
334 | } | |
335 | ||
336 | /* | |
337 | * mask must be 0xFFFFFFFF or 0x00000000. | |
338 | * | |
339 | * if (mask) { | |
340 | * uint64_t tmp = *a; | |
341 | * | |
342 | * *a = *b; | |
343 | * *b = tmp; | |
344 | * } | |
345 | */ | |
346 | static ossl_inline void constant_time_cond_swap_64(uint64_t mask, uint64_t *a, | |
347 | uint64_t *b) | |
348 | { | |
349 | uint64_t xor = *a ^ *b; | |
350 | ||
351 | xor &= mask; | |
352 | *a ^= xor; | |
353 | *b ^= xor; | |
354 | } | |
355 | ||
677c4a01 PS |
356 | /* |
357 | * mask must be 0xFF or 0x00. | |
358 | * "constant time" is per len. | |
359 | * | |
360 | * if (mask) { | |
361 | * unsigned char tmp[len]; | |
362 | * | |
363 | * memcpy(tmp, a, len); | |
364 | * memcpy(a, b); | |
365 | * memcpy(b, tmp); | |
366 | * } | |
367 | */ | |
368 | static ossl_inline void constant_time_cond_swap_buff(unsigned char mask, | |
369 | unsigned char *a, | |
370 | unsigned char *b, | |
371 | size_t len) | |
372 | { | |
373 | size_t i; | |
374 | unsigned char tmp; | |
375 | ||
376 | for (i = 0; i < len; i++) { | |
377 | tmp = a[i] ^ b[i]; | |
378 | tmp &= mask; | |
379 | a[i] ^= tmp; | |
380 | b[i] ^= tmp; | |
381 | } | |
382 | } | |
383 | ||
e0fa6324 MC |
384 | /* |
385 | * table is a two dimensional array of bytes. Each row has rowsize elements. | |
386 | * Copies row number idx into out. rowsize and numrows are not considered | |
387 | * private. | |
388 | */ | |
389 | static ossl_inline void constant_time_lookup(void *out, | |
390 | const void *table, | |
391 | size_t rowsize, | |
392 | size_t numrows, | |
393 | size_t idx) | |
394 | { | |
395 | size_t i, j; | |
396 | const unsigned char *tablec = (const unsigned char *)table; | |
397 | unsigned char *outc = (unsigned char *)out; | |
398 | unsigned char mask; | |
399 | ||
400 | memset(out, 0, rowsize); | |
401 | ||
402 | /* Note idx may underflow - but that is well defined */ | |
403 | for (i = 0; i < numrows; i++, idx--) { | |
404 | mask = (unsigned char)constant_time_is_zero_s(idx); | |
405 | for (j = 0; j < rowsize; j++) | |
406 | *(outc + j) |= constant_time_select_8(mask, *(tablec++), 0); | |
407 | } | |
408 | } | |
409 | ||
f658a3b6 AP |
410 | /* |
411 | * Expected usage pattern is to unconditionally set error and then | |
412 | * wipe it if there was no actual error. |clear| is 1 or 0. | |
413 | */ | |
414 | void err_clear_last_constant_time(int clear); | |
415 | ||
ae4186b0 | 416 | #endif /* OSSL_INTERNAL_CONSTANT_TIME_H */ |