1/*
2 * Copyright 2014-2018 The OpenSSL Project Authors. All Rights Reserved.
3 *
4 * Licensed under the Apache License 2.0 (the "License"). You may not use
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
8 */
9
10#ifndef OSSL_INTERNAL_CONSTANT_TIME_H
11# define OSSL_INTERNAL_CONSTANT_TIME_H
12
13# include <stdlib.h>
14# include <string.h>
15# include <openssl/e_os2.h> /* For 'ossl_inline' */
16
17/*-
18 * The boolean methods return a bitmask of all ones (0xff...f) for true
19 * and 0 for false. This is useful for choosing a value based on the result
20 * of a conditional in constant time. For example,
21 * if (a < b) {
22 * c = a;
23 * } else {
24 * c = b;
25 * }
26 * can be written as
27 * unsigned int lt = constant_time_lt(a, b);
28 * c = constant_time_select(lt, a, b);
29 */
30
31/* Returns the given value with the MSB copied to all the other bits. */
32static ossl_inline unsigned int constant_time_msb(unsigned int a);
33/* Convenience method for uint32_t. */
34static ossl_inline uint32_t constant_time_msb_32(uint32_t a);
35/* Convenience method for uint64_t. */
36static ossl_inline uint64_t constant_time_msb_64(uint64_t a);
37
38/* Returns 0xff..f if a < b and 0 otherwise. */
39static ossl_inline unsigned int constant_time_lt(unsigned int a,
40 unsigned int b);
41/* Convenience method for getting an 8-bit mask. */
42static ossl_inline unsigned char constant_time_lt_8(unsigned int a,
43 unsigned int b);
44/* Convenience method for uint64_t. */
45static ossl_inline uint64_t constant_time_lt_64(uint64_t a, uint64_t b);
46
47/* Returns 0xff..f if a >= b and 0 otherwise. */
48static ossl_inline unsigned int constant_time_ge(unsigned int a,
49 unsigned int b);
50/* Convenience method for getting an 8-bit mask. */
51static ossl_inline unsigned char constant_time_ge_8(unsigned int a,
52 unsigned int b);
53
54/* Returns 0xff..f if a == 0 and 0 otherwise. */
55static ossl_inline unsigned int constant_time_is_zero(unsigned int a);
56/* Convenience method for getting an 8-bit mask. */
57static ossl_inline unsigned char constant_time_is_zero_8(unsigned int a);
58/* Convenience method for getting a 32-bit mask. */
59static ossl_inline uint32_t constant_time_is_zero_32(uint32_t a);
60
61/* Returns 0xff..f if a == b and 0 otherwise. */
62static ossl_inline unsigned int constant_time_eq(unsigned int a,
63 unsigned int b);
64/* Convenience method for getting an 8-bit mask. */
65static ossl_inline unsigned char constant_time_eq_8(unsigned int a,
66 unsigned int b);
67/* Signed integers. */
68static ossl_inline unsigned int constant_time_eq_int(int a, int b);
69/* Convenience method for getting an 8-bit mask. */
70static ossl_inline unsigned char constant_time_eq_int_8(int a, int b);
71
72/*-
73 * Returns (mask & a) | (~mask & b).
74 *
75 * When |mask| is all 1s or all 0s (as returned by the methods above),
76 * the select methods return either |a| (if |mask| is nonzero) or |b|
77 * (if |mask| is zero).
78 */
79static ossl_inline unsigned int constant_time_select(unsigned int mask,
80 unsigned int a,
81 unsigned int b);
82/* Convenience method for unsigned chars. */
83static ossl_inline unsigned char constant_time_select_8(unsigned char mask,
84 unsigned char a,
85 unsigned char b);
86
87/* Convenience method for uint32_t. */
88static ossl_inline uint32_t constant_time_select_32(uint32_t mask, uint32_t a,
89 uint32_t b);
90
91/* Convenience method for uint64_t. */
92static ossl_inline uint64_t constant_time_select_64(uint64_t mask, uint64_t a,
93 uint64_t b);
94/* Convenience method for signed integers. */
95static ossl_inline int constant_time_select_int(unsigned int mask, int a,
96 int b);
97
98
99static ossl_inline unsigned int constant_time_msb(unsigned int a)
100{
101 return 0 - (a >> (sizeof(a) * 8 - 1));
102}
103
104
105static ossl_inline uint32_t constant_time_msb_32(uint32_t a)
106{
107 return 0 - (a >> 31);
108}
109
110static ossl_inline uint64_t constant_time_msb_64(uint64_t a)
111{
112 return 0 - (a >> 63);
113}
114
115static ossl_inline size_t constant_time_msb_s(size_t a)
116{
117 return 0 - (a >> (sizeof(a) * 8 - 1));
118}
119
120static ossl_inline unsigned int constant_time_lt(unsigned int a,
121 unsigned int b)
122{
123 return constant_time_msb(a ^ ((a ^ b) | ((a - b) ^ b)));
124}
125
126static ossl_inline size_t constant_time_lt_s(size_t a, size_t b)
127{
128 return constant_time_msb_s(a ^ ((a ^ b) | ((a - b) ^ b)));
129}
130
131static ossl_inline unsigned char constant_time_lt_8(unsigned int a,
132 unsigned int b)
133{
134 return (unsigned char)constant_time_lt(a, b);
135}
136
137static ossl_inline uint64_t constant_time_lt_64(uint64_t a, uint64_t b)
138{
139 return constant_time_msb_64(a ^ ((a ^ b) | ((a - b) ^ b)));
140}
141
142static ossl_inline unsigned int constant_time_ge(unsigned int a,
143 unsigned int b)
144{
145 return ~constant_time_lt(a, b);
146}
147
148static ossl_inline size_t constant_time_ge_s(size_t a, size_t b)
149{
150 return ~constant_time_lt_s(a, b);
151}
152
153static ossl_inline unsigned char constant_time_ge_8(unsigned int a,
154 unsigned int b)
155{
156 return (unsigned char)constant_time_ge(a, b);
157}
158
159static ossl_inline unsigned char constant_time_ge_8_s(size_t a, size_t b)
160{
161 return (unsigned char)constant_time_ge_s(a, b);
162}
163
164static ossl_inline unsigned int constant_time_is_zero(unsigned int a)
165{
166 return constant_time_msb(~a & (a - 1));
167}
168
169static ossl_inline size_t constant_time_is_zero_s(size_t a)
170{
171 return constant_time_msb_s(~a & (a - 1));
172}
173
174static ossl_inline unsigned char constant_time_is_zero_8(unsigned int a)
175{
176 return (unsigned char)constant_time_is_zero(a);
177}
178
179static ossl_inline uint32_t constant_time_is_zero_32(uint32_t a)
180{
181 return constant_time_msb_32(~a & (a - 1));
182}
183
184static ossl_inline unsigned int constant_time_eq(unsigned int a,
185 unsigned int b)
186{
187 return constant_time_is_zero(a ^ b);
188}
189
190static ossl_inline size_t constant_time_eq_s(size_t a, size_t b)
191{
192 return constant_time_is_zero_s(a ^ b);
193}
194
195static ossl_inline unsigned char constant_time_eq_8(unsigned int a,
196 unsigned int b)
197{
198 return (unsigned char)constant_time_eq(a, b);
199}
200
201static ossl_inline unsigned char constant_time_eq_8_s(size_t a, size_t b)
202{
203 return (unsigned char)constant_time_eq_s(a, b);
204}
205
206static ossl_inline unsigned int constant_time_eq_int(int a, int b)
207{
208 return constant_time_eq((unsigned)(a), (unsigned)(b));
209}
210
211static ossl_inline unsigned char constant_time_eq_int_8(int a, int b)
212{
213 return constant_time_eq_8((unsigned)(a), (unsigned)(b));
214}
215
216/*
217 * Returns the value unmodified, but avoids optimizations.
218 * The barriers prevent the compiler from narrowing down the
219 * possible value range of the mask and ~mask in the select
220 * statements, which avoids the recognition of the select
221 * and turning it into a conditional load or branch.
222 */
223static ossl_inline unsigned int value_barrier(unsigned int a)
224{
225#if !defined(OPENSSL_NO_ASM) && defined(__GNUC__)
226 unsigned int r;
227 __asm__("" : "=r"(r) : "0"(a));
228#else
229 volatile unsigned int r = a;
230#endif
231 return r;
232}
233
234/* Convenience method for uint32_t. */
235static ossl_inline uint32_t value_barrier_32(uint32_t a)
236{
237#if !defined(OPENSSL_NO_ASM) && defined(__GNUC__)
238 uint32_t r;
239 __asm__("" : "=r"(r) : "0"(a));
240#else
241 volatile uint32_t r = a;
242#endif
243 return r;
244}
245
246/* Convenience method for uint64_t. */
247static ossl_inline uint64_t value_barrier_64(uint64_t a)
248{
249#if !defined(OPENSSL_NO_ASM) && defined(__GNUC__)
250 uint64_t r;
251 __asm__("" : "=r"(r) : "0"(a));
252#else
253 volatile uint64_t r = a;
254#endif
255 return r;
256}
257
258/* Convenience method for size_t. */
259static ossl_inline size_t value_barrier_s(size_t a)
260{
261#if !defined(OPENSSL_NO_ASM) && defined(__GNUC__)
262 size_t r;
263 __asm__("" : "=r"(r) : "0"(a));
264#else
265 volatile size_t r = a;
266#endif
267 return r;
268}
269
270static ossl_inline unsigned int constant_time_select(unsigned int mask,
271 unsigned int a,
272 unsigned int b)
273{
274 return (value_barrier(mask) & a) | (value_barrier(~mask) & b);
275}
276
277static ossl_inline size_t constant_time_select_s(size_t mask,
278 size_t a,
279 size_t b)
280{
281 return (value_barrier_s(mask) & a) | (value_barrier_s(~mask) & b);
282}
283
284static ossl_inline unsigned char constant_time_select_8(unsigned char mask,
285 unsigned char a,
286 unsigned char b)
287{
288 return (unsigned char)constant_time_select(mask, a, b);
289}
290
291static ossl_inline int constant_time_select_int(unsigned int mask, int a,
292 int b)
293{
294 return (int)constant_time_select(mask, (unsigned)(a), (unsigned)(b));
295}
296
297static ossl_inline int constant_time_select_int_s(size_t mask, int a, int b)
298{
299 return (int)constant_time_select((unsigned)mask, (unsigned)(a),
300 (unsigned)(b));
301}
302
303static ossl_inline uint32_t constant_time_select_32(uint32_t mask, uint32_t a,
304 uint32_t b)
305{
306 return (value_barrier_32(mask) & a) | (value_barrier_32(~mask) & b);
307}
308
309static ossl_inline uint64_t constant_time_select_64(uint64_t mask, uint64_t a,
310 uint64_t b)
311{
312 return (value_barrier_64(mask) & a) | (value_barrier_64(~mask) & b);
313}
314
315/*
316 * mask must be 0xFFFFFFFF or 0x00000000.
317 *
318 * if (mask) {
319 * uint32_t tmp = *a;
320 *
321 * *a = *b;
322 * *b = tmp;
323 * }
324 */
325static ossl_inline void constant_time_cond_swap_32(uint32_t mask, uint32_t *a,
326 uint32_t *b)
327{
328 uint32_t xor = *a ^ *b;
329
330 xor &= mask;
331 *a ^= xor;
332 *b ^= xor;
333}
334
335/*
336 * mask must be 0xFFFFFFFF or 0x00000000.
337 *
338 * if (mask) {
339 * uint64_t tmp = *a;
340 *
341 * *a = *b;
342 * *b = tmp;
343 * }
344 */
345static ossl_inline void constant_time_cond_swap_64(uint64_t mask, uint64_t *a,
346 uint64_t *b)
347{
348 uint64_t xor = *a ^ *b;
349
350 xor &= mask;
351 *a ^= xor;
352 *b ^= xor;
353}
354
355/*
356 * mask must be 0xFF or 0x00.
357 * "constant time" is per len.
358 *
359 * if (mask) {
360 * unsigned char tmp[len];
361 *
362 * memcpy(tmp, a, len);
363 * memcpy(a, b);
364 * memcpy(b, tmp);
365 * }
366 */
367static ossl_inline void constant_time_cond_swap_buff(unsigned char mask,
368 unsigned char *a,
369 unsigned char *b,
370 size_t len)
371{
372 size_t i;
373 unsigned char tmp;
374
375 for (i = 0; i < len; i++) {
376 tmp = a[i] ^ b[i];
377 tmp &= mask;
378 a[i] ^= tmp;
379 b[i] ^= tmp;
380 }
381}
382
383/*
384 * table is a two dimensional array of bytes. Each row has rowsize elements.
385 * Copies row number idx into out. rowsize and numrows are not considered
386 * private.
387 */
388static ossl_inline void constant_time_lookup(void *out,
389 const void *table,
390 size_t rowsize,
391 size_t numrows,
392 size_t idx)
393{
394 size_t i, j;
395 const unsigned char *tablec = (const unsigned char *)table;
396 unsigned char *outc = (unsigned char *)out;
397 unsigned char mask;
398
399 memset(out, 0, rowsize);
400
401 /* Note idx may underflow - but that is well defined */
402 for (i = 0; i < numrows; i++, idx--) {
403 mask = (unsigned char)constant_time_is_zero_s(idx);
404 for (j = 0; j < rowsize; j++)
405 *(outc + j) |= constant_time_select_8(mask, *(tablec++), 0);
406 }
407}
408
409/*
410 * Expected usage pattern is to unconditionally set error and then
411 * wipe it if there was no actual error. |clear| is 1 or 0.
412 */
413void err_clear_last_constant_time(int clear);
414
415#endif /* OSSL_INTERNAL_CONSTANT_TIME_H */
416