1/*
2 * Copyright 2014-2021 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# pragma once
13
14# include <stdlib.h>
15# include <string.h>
16# include <openssl/e_os2.h>              /* For 'ossl_inline' */
17
18/*-
19 * The boolean methods return a bitmask of all ones (0xff...f) for true
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,
22 *      if (a < b) {
23 *        c = a;
24 *      } else {
25 *        c = b;
26 *      }
27 * can be written as
28 *      unsigned int lt = constant_time_lt(a, b);
29 *      c = constant_time_select(lt, a, b);
30 */
31
32/* Returns the given value with the MSB copied to all the other bits. */
33static ossl_inline unsigned int constant_time_msb(unsigned int a);
34/* Convenience method for uint32_t. */
35static ossl_inline uint32_t constant_time_msb_32(uint32_t a);
36/* Convenience method for uint64_t. */
37static ossl_inline uint64_t constant_time_msb_64(uint64_t a);
38
39/* Returns 0xff..f if a < b and 0 otherwise. */
40static ossl_inline unsigned int constant_time_lt(unsigned int a,
41                                                 unsigned int b);
42/* Convenience method for getting an 8-bit mask. */
43static ossl_inline unsigned char constant_time_lt_8(unsigned int a,
44                                                    unsigned int b);
45/* Convenience method for uint64_t. */
46static ossl_inline uint64_t constant_time_lt_64(uint64_t a, uint64_t b);
47
48/* Returns 0xff..f if a >= b and 0 otherwise. */
49static ossl_inline unsigned int constant_time_ge(unsigned int a,
50                                                 unsigned int b);
51/* Convenience method for getting an 8-bit mask. */
52static ossl_inline unsigned char constant_time_ge_8(unsigned int a,
53                                                    unsigned int b);
54
55/* Returns 0xff..f if a == 0 and 0 otherwise. */
56static ossl_inline unsigned int constant_time_is_zero(unsigned int a);
57/* Convenience method for getting an 8-bit mask. */
58static ossl_inline unsigned char constant_time_is_zero_8(unsigned int a);
59/* Convenience method for getting a 32-bit mask. */
60static ossl_inline uint32_t constant_time_is_zero_32(uint32_t a);
61
62/* Returns 0xff..f if a == b and 0 otherwise. */
63static ossl_inline unsigned int constant_time_eq(unsigned int a,
64                                                 unsigned int b);
65/* Convenience method for getting an 8-bit mask. */
66static ossl_inline unsigned char constant_time_eq_8(unsigned int a,
67                                                    unsigned int b);
68/* Signed integers. */
69static ossl_inline unsigned int constant_time_eq_int(int a, int b);
70/* Convenience method for getting an 8-bit mask. */
71static ossl_inline unsigned char constant_time_eq_int_8(int a, int b);
72
73/*-
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 */
80static ossl_inline unsigned int constant_time_select(unsigned int mask,
81                                                     unsigned int a,
82                                                     unsigned int b);
83/* Convenience method for unsigned chars. */
84static ossl_inline unsigned char constant_time_select_8(unsigned char mask,
85                                                        unsigned char a,
86                                                        unsigned char b);
87
88/* Convenience method for uint32_t. */
89static ossl_inline uint32_t constant_time_select_32(uint32_t mask, uint32_t a,
90                                                    uint32_t b);
91
92/* Convenience method for uint64_t. */
93static ossl_inline uint64_t constant_time_select_64(uint64_t mask, uint64_t a,
94                                                    uint64_t b);
95/* Convenience method for signed integers. */
96static ossl_inline int constant_time_select_int(unsigned int mask, int a,
97                                                int b);
98
99
100static ossl_inline unsigned int constant_time_msb(unsigned int a)
101{
102    return 0 - (a >> (sizeof(a) * 8 - 1));
103}
104
105
106static ossl_inline uint32_t constant_time_msb_32(uint32_t a)
107{
108    return 0 - (a >> 31);
109}
110
111static ossl_inline uint64_t constant_time_msb_64(uint64_t a)
112{
113    return 0 - (a >> 63);
114}
115
116static ossl_inline size_t constant_time_msb_s(size_t a)
117{
118    return 0 - (a >> (sizeof(a) * 8 - 1));
119}
120
121static ossl_inline unsigned int constant_time_lt(unsigned int a,
122                                                 unsigned int b)
123{
124    return constant_time_msb(a ^ ((a ^ b) | ((a - b) ^ b)));
125}
126
127static 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
132static ossl_inline unsigned char constant_time_lt_8(unsigned int a,
133                                                    unsigned int b)
134{
135    return (unsigned char)constant_time_lt(a, b);
136}
137
138static 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
143static ossl_inline unsigned int constant_time_ge(unsigned int a,
144                                                 unsigned int b)
145{
146    return ~constant_time_lt(a, b);
147}
148
149static 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
154static ossl_inline unsigned char constant_time_ge_8(unsigned int a,
155                                                    unsigned int b)
156{
157    return (unsigned char)constant_time_ge(a, b);
158}
159
160static ossl_inline unsigned char constant_time_ge_8_s(size_t a, size_t b)
161{
162    return (unsigned char)constant_time_ge_s(a, b);
163}
164
165static ossl_inline unsigned int constant_time_is_zero(unsigned int a)
166{
167    return constant_time_msb(~a & (a - 1));
168}
169
170static ossl_inline size_t constant_time_is_zero_s(size_t a)
171{
172    return constant_time_msb_s(~a & (a - 1));
173}
174
175static ossl_inline unsigned char constant_time_is_zero_8(unsigned int a)
176{
177    return (unsigned char)constant_time_is_zero(a);
178}
179
180static ossl_inline uint32_t constant_time_is_zero_32(uint32_t a)
181{
182    return constant_time_msb_32(~a & (a - 1));
183}
184
185static ossl_inline uint64_t constant_time_is_zero_64(uint64_t a)
186{
187    return constant_time_msb_64(~a & (a - 1));
188}
189
190static ossl_inline unsigned int constant_time_eq(unsigned int a,
191                                                 unsigned int b)
192{
193    return constant_time_is_zero(a ^ b);
194}
195
196static ossl_inline size_t constant_time_eq_s(size_t a, size_t b)
197{
198    return constant_time_is_zero_s(a ^ b);
199}
200
201static ossl_inline unsigned char constant_time_eq_8(unsigned int a,
202                                                    unsigned int b)
203{
204    return (unsigned char)constant_time_eq(a, b);
205}
206
207static ossl_inline unsigned char constant_time_eq_8_s(size_t a, size_t b)
208{
209    return (unsigned char)constant_time_eq_s(a, b);
210}
211
212static ossl_inline unsigned int constant_time_eq_int(int a, int b)
213{
214    return constant_time_eq((unsigned)(a), (unsigned)(b));
215}
216
217static ossl_inline unsigned char constant_time_eq_int_8(int a, int b)
218{
219    return constant_time_eq_8((unsigned)(a), (unsigned)(b));
220}
221
222/*
223 * Returns the value unmodified, but avoids optimizations.
224 * The barriers prevent the compiler from narrowing down the
225 * possible value range of the mask and ~mask in the select
226 * statements, which avoids the recognition of the select
227 * and turning it into a conditional load or branch.
228 */
229static ossl_inline unsigned int value_barrier(unsigned int a)
230{
231#if !defined(OPENSSL_NO_ASM) && defined(__GNUC__)
232    unsigned int r;
233    __asm__("" : "=r"(r) : "0"(a));
234#else
235    volatile unsigned int r = a;
236#endif
237    return r;
238}
239
240/* Convenience method for uint32_t. */
241static ossl_inline uint32_t value_barrier_32(uint32_t a)
242{
243#if !defined(OPENSSL_NO_ASM) && defined(__GNUC__)
244    uint32_t r;
245    __asm__("" : "=r"(r) : "0"(a));
246#else
247    volatile uint32_t r = a;
248#endif
249    return r;
250}
251
252/* Convenience method for uint64_t. */
253static ossl_inline uint64_t value_barrier_64(uint64_t a)
254{
255#if !defined(OPENSSL_NO_ASM) && defined(__GNUC__)
256    uint64_t r;
257    __asm__("" : "=r"(r) : "0"(a));
258#else
259    volatile uint64_t r = a;
260#endif
261    return r;
262}
263
264/* Convenience method for size_t. */
265static ossl_inline size_t value_barrier_s(size_t a)
266{
267#if !defined(OPENSSL_NO_ASM) && defined(__GNUC__)
268    size_t r;
269    __asm__("" : "=r"(r) : "0"(a));
270#else
271    volatile size_t r = a;
272#endif
273    return r;
274}
275
276static ossl_inline unsigned int constant_time_select(unsigned int mask,
277                                                     unsigned int a,
278                                                     unsigned int b)
279{
280    return (value_barrier(mask) & a) | (value_barrier(~mask) & b);
281}
282
283static ossl_inline size_t constant_time_select_s(size_t mask,
284                                                 size_t a,
285                                                 size_t b)
286{
287    return (value_barrier_s(mask) & a) | (value_barrier_s(~mask) & b);
288}
289
290static ossl_inline unsigned char constant_time_select_8(unsigned char mask,
291                                                        unsigned char a,
292                                                        unsigned char b)
293{
294    return (unsigned char)constant_time_select(mask, a, b);
295}
296
297static ossl_inline int constant_time_select_int(unsigned int mask, int a,
298                                                int b)
299{
300    return (int)constant_time_select(mask, (unsigned)(a), (unsigned)(b));
301}
302
303static ossl_inline int constant_time_select_int_s(size_t mask, int a, int b)
304{
305    return (int)constant_time_select((unsigned)mask, (unsigned)(a),
306                                      (unsigned)(b));
307}
308
309static ossl_inline uint32_t constant_time_select_32(uint32_t mask, uint32_t a,
310                                                    uint32_t b)
311{
312    return (value_barrier_32(mask) & a) | (value_barrier_32(~mask) & b);
313}
314
315static ossl_inline uint64_t constant_time_select_64(uint64_t mask, uint64_t a,
316                                                    uint64_t b)
317{
318    return (value_barrier_64(mask) & a) | (value_barrier_64(~mask) & b);
319}
320
321/*
322 * mask must be 0xFFFFFFFF or 0x00000000.
323 *
324 * if (mask) {
325 *     uint32_t tmp = *a;
326 *
327 *     *a = *b;
328 *     *b = tmp;
329 * }
330 */
331static ossl_inline void constant_time_cond_swap_32(uint32_t mask, uint32_t *a,
332                                                   uint32_t *b)
333{
334    uint32_t xor = *a ^ *b;
335
336    xor &= mask;
337    *a ^= xor;
338    *b ^= xor;
339}
340
341/*
342 * mask must be 0xFFFFFFFF or 0x00000000.
343 *
344 * if (mask) {
345 *     uint64_t tmp = *a;
346 *
347 *     *a = *b;
348 *     *b = tmp;
349 * }
350 */
351static ossl_inline void constant_time_cond_swap_64(uint64_t mask, uint64_t *a,
352                                                   uint64_t *b)
353{
354    uint64_t xor = *a ^ *b;
355
356    xor &= mask;
357    *a ^= xor;
358    *b ^= xor;
359}
360
361/*
362 * mask must be 0xFF or 0x00.
363 * "constant time" is per len.
364 *
365 * if (mask) {
366 *     unsigned char tmp[len];
367 *
368 *     memcpy(tmp, a, len);
369 *     memcpy(a, b);
370 *     memcpy(b, tmp);
371 * }
372 */
373static ossl_inline void constant_time_cond_swap_buff(unsigned char mask,
374                                                     unsigned char *a,
375                                                     unsigned char *b,
376                                                     size_t len)
377{
378    size_t i;
379    unsigned char tmp;
380
381    for (i = 0; i < len; i++) {
382        tmp = a[i] ^ b[i];
383        tmp &= mask;
384        a[i] ^= tmp;
385        b[i] ^= tmp;
386    }
387}
388
389/*
390 * table is a two dimensional array of bytes. Each row has rowsize elements.
391 * Copies row number idx into out. rowsize and numrows are not considered
392 * private.
393 */
394static ossl_inline void constant_time_lookup(void *out,
395                                             const void *table,
396                                             size_t rowsize,
397                                             size_t numrows,
398                                             size_t idx)
399{
400    size_t i, j;
401    const unsigned char *tablec = (const unsigned char *)table;
402    unsigned char *outc = (unsigned char *)out;
403    unsigned char mask;
404
405    memset(out, 0, rowsize);
406
407    /* Note idx may underflow - but that is well defined */
408    for (i = 0; i < numrows; i++, idx--) {
409        mask = (unsigned char)constant_time_is_zero_s(idx);
410        for (j = 0; j < rowsize; j++)
411            *(outc + j) |= constant_time_select_8(mask, *(tablec++), 0);
412    }
413}
414
415/*
416 * Expected usage pattern is to unconditionally set error and then
417 * wipe it if there was no actual error. |clear| is 1 or 0.
418 */
419void err_clear_last_constant_time(int clear);
420
421#endif                          /* OSSL_INTERNAL_CONSTANT_TIME_H */
422