1 /*
2 * Copyright 2000-2019 The OpenSSL Project Authors. All Rights Reserved.
3 *
4 * Licensed under the OpenSSL license (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 #include "internal/cryptlib.h"
11 #include "bn_local.h"
12
13 /*-
14 * TODO list
15 *
16 * 1. Check a bunch of "(words+1)" type hacks in various bignum functions and
17 * check they can be safely removed.
18 * - Check +1 and other ugliness in BN_from_montgomery()
19 *
20 * 2. Consider allowing a BN_new_ex() that, at least, lets you specify an
21 * appropriate 'block' size that will be honoured by bn_expand_internal() to
22 * prevent piddly little reallocations. OTOH, profiling bignum expansions in
23 * BN_CTX doesn't show this to be a big issue.
24 */
25
26 /* How many bignums are in each "pool item"; */
27 #define BN_CTX_POOL_SIZE 16
28 /* The stack frame info is resizing, set a first-time expansion size; */
29 #define BN_CTX_START_FRAMES 32
30
31 /***********/
32 /* BN_POOL */
33 /***********/
34
35 /* A bundle of bignums that can be linked with other bundles */
36 typedef struct bignum_pool_item {
37 /* The bignum values */
38 BIGNUM vals[BN_CTX_POOL_SIZE];
39 /* Linked-list admin */
40 struct bignum_pool_item *prev, *next;
41 } BN_POOL_ITEM;
42 /* A linked-list of bignums grouped in bundles */
43 typedef struct bignum_pool {
44 /* Linked-list admin */
45 BN_POOL_ITEM *head, *current, *tail;
46 /* Stack depth and allocation size */
47 unsigned used, size;
48 } BN_POOL;
49 static void BN_POOL_init(BN_POOL *);
50 static void BN_POOL_finish(BN_POOL *);
51 static BIGNUM *BN_POOL_get(BN_POOL *, int);
52 static void BN_POOL_release(BN_POOL *, unsigned int);
53
54 /************/
55 /* BN_STACK */
56 /************/
57
58 /* A wrapper to manage the "stack frames" */
59 typedef struct bignum_ctx_stack {
60 /* Array of indexes into the bignum stack */
61 unsigned int *indexes;
62 /* Number of stack frames, and the size of the allocated array */
63 unsigned int depth, size;
64 } BN_STACK;
65 static void BN_STACK_init(BN_STACK *);
66 static void BN_STACK_finish(BN_STACK *);
67 static int BN_STACK_push(BN_STACK *, unsigned int);
68 static unsigned int BN_STACK_pop(BN_STACK *);
69
70 /**********/
71 /* BN_CTX */
72 /**********/
73
74 /* The opaque BN_CTX type */
75 struct bignum_ctx {
76 /* The bignum bundles */
77 BN_POOL pool;
78 /* The "stack frames", if you will */
79 BN_STACK stack;
80 /* The number of bignums currently assigned */
81 unsigned int used;
82 /* Depth of stack overflow */
83 int err_stack;
84 /* Block "gets" until an "end" (compatibility behaviour) */
85 int too_many;
86 /* Flags. */
87 int flags;
88 };
89
90 /* Enable this to find BN_CTX bugs */
91 #ifdef BN_CTX_DEBUG
92 static const char *ctxdbg_cur = NULL;
ctxdbg(BN_CTX * ctx)93 static void ctxdbg(BN_CTX *ctx)
94 {
95 unsigned int bnidx = 0, fpidx = 0;
96 BN_POOL_ITEM *item = ctx->pool.head;
97 BN_STACK *stack = &ctx->stack;
98 fprintf(stderr, "(%16p): ", ctx);
99 while (bnidx < ctx->used) {
100 fprintf(stderr, "%03x ", item->vals[bnidx++ % BN_CTX_POOL_SIZE].dmax);
101 if (!(bnidx % BN_CTX_POOL_SIZE))
102 item = item->next;
103 }
104 fprintf(stderr, "\n");
105 bnidx = 0;
106 fprintf(stderr, " : ");
107 while (fpidx < stack->depth) {
108 while (bnidx++ < stack->indexes[fpidx])
109 fprintf(stderr, " ");
110 fprintf(stderr, "^^^ ");
111 bnidx++;
112 fpidx++;
113 }
114 fprintf(stderr, "\n");
115 }
116
117 # define CTXDBG_ENTRY(str, ctx) do { \
118 ctxdbg_cur = (str); \
119 fprintf(stderr,"Starting %s\n", ctxdbg_cur); \
120 ctxdbg(ctx); \
121 } while(0)
122 # define CTXDBG_EXIT(ctx) do { \
123 fprintf(stderr,"Ending %s\n", ctxdbg_cur); \
124 ctxdbg(ctx); \
125 } while(0)
126 # define CTXDBG_RET(ctx,ret)
127 #else
128 # define CTXDBG_ENTRY(str, ctx)
129 # define CTXDBG_EXIT(ctx)
130 # define CTXDBG_RET(ctx,ret)
131 #endif
132
133
BN_CTX_new(void)134 BN_CTX *BN_CTX_new(void)
135 {
136 BN_CTX *ret;
137
138 if ((ret = OPENSSL_zalloc(sizeof(*ret))) == NULL) {
139 BNerr(BN_F_BN_CTX_NEW, ERR_R_MALLOC_FAILURE);
140 return NULL;
141 }
142 /* Initialise the structure */
143 BN_POOL_init(&ret->pool);
144 BN_STACK_init(&ret->stack);
145 return ret;
146 }
147
BN_CTX_secure_new(void)148 BN_CTX *BN_CTX_secure_new(void)
149 {
150 BN_CTX *ret = BN_CTX_new();
151
152 if (ret != NULL)
153 ret->flags = BN_FLG_SECURE;
154 return ret;
155 }
156
BN_CTX_free(BN_CTX * ctx)157 void BN_CTX_free(BN_CTX *ctx)
158 {
159 if (ctx == NULL)
160 return;
161 #ifdef BN_CTX_DEBUG
162 {
163 BN_POOL_ITEM *pool = ctx->pool.head;
164 fprintf(stderr, "BN_CTX_free, stack-size=%d, pool-bignums=%d\n",
165 ctx->stack.size, ctx->pool.size);
166 fprintf(stderr, "dmaxs: ");
167 while (pool) {
168 unsigned loop = 0;
169 while (loop < BN_CTX_POOL_SIZE)
170 fprintf(stderr, "%02x ", pool->vals[loop++].dmax);
171 pool = pool->next;
172 }
173 fprintf(stderr, "\n");
174 }
175 #endif
176 BN_STACK_finish(&ctx->stack);
177 BN_POOL_finish(&ctx->pool);
178 OPENSSL_free(ctx);
179 }
180
BN_CTX_start(BN_CTX * ctx)181 void BN_CTX_start(BN_CTX *ctx)
182 {
183 CTXDBG_ENTRY("BN_CTX_start", ctx);
184 /* If we're already overflowing ... */
185 if (ctx->err_stack || ctx->too_many)
186 ctx->err_stack++;
187 /* (Try to) get a new frame pointer */
188 else if (!BN_STACK_push(&ctx->stack, ctx->used)) {
189 BNerr(BN_F_BN_CTX_START, BN_R_TOO_MANY_TEMPORARY_VARIABLES);
190 ctx->err_stack++;
191 }
192 CTXDBG_EXIT(ctx);
193 }
194
BN_CTX_end(BN_CTX * ctx)195 void BN_CTX_end(BN_CTX *ctx)
196 {
197 if (ctx == NULL)
198 return;
199 CTXDBG_ENTRY("BN_CTX_end", ctx);
200 if (ctx->err_stack)
201 ctx->err_stack--;
202 else {
203 unsigned int fp = BN_STACK_pop(&ctx->stack);
204 /* Does this stack frame have anything to release? */
205 if (fp < ctx->used)
206 BN_POOL_release(&ctx->pool, ctx->used - fp);
207 ctx->used = fp;
208 /* Unjam "too_many" in case "get" had failed */
209 ctx->too_many = 0;
210 }
211 CTXDBG_EXIT(ctx);
212 }
213
BN_CTX_get(BN_CTX * ctx)214 BIGNUM *BN_CTX_get(BN_CTX *ctx)
215 {
216 BIGNUM *ret;
217
218 CTXDBG_ENTRY("BN_CTX_get", ctx);
219 if (ctx->err_stack || ctx->too_many)
220 return NULL;
221 if ((ret = BN_POOL_get(&ctx->pool, ctx->flags)) == NULL) {
222 /*
223 * Setting too_many prevents repeated "get" attempts from cluttering
224 * the error stack.
225 */
226 ctx->too_many = 1;
227 BNerr(BN_F_BN_CTX_GET, BN_R_TOO_MANY_TEMPORARY_VARIABLES);
228 return NULL;
229 }
230 /* OK, make sure the returned bignum is "zero" */
231 BN_zero(ret);
232 /* clear BN_FLG_CONSTTIME if leaked from previous frames */
233 ret->flags &= (~BN_FLG_CONSTTIME);
234 ctx->used++;
235 CTXDBG_RET(ctx, ret);
236 return ret;
237 }
238
239 /************/
240 /* BN_STACK */
241 /************/
242
BN_STACK_init(BN_STACK * st)243 static void BN_STACK_init(BN_STACK *st)
244 {
245 st->indexes = NULL;
246 st->depth = st->size = 0;
247 }
248
BN_STACK_finish(BN_STACK * st)249 static void BN_STACK_finish(BN_STACK *st)
250 {
251 OPENSSL_free(st->indexes);
252 st->indexes = NULL;
253 }
254
255
BN_STACK_push(BN_STACK * st,unsigned int idx)256 static int BN_STACK_push(BN_STACK *st, unsigned int idx)
257 {
258 if (st->depth == st->size) {
259 /* Need to expand */
260 unsigned int newsize =
261 st->size ? (st->size * 3 / 2) : BN_CTX_START_FRAMES;
262 unsigned int *newitems;
263
264 if ((newitems = OPENSSL_malloc(sizeof(*newitems) * newsize)) == NULL) {
265 BNerr(BN_F_BN_STACK_PUSH, ERR_R_MALLOC_FAILURE);
266 return 0;
267 }
268 if (st->depth)
269 memcpy(newitems, st->indexes, sizeof(*newitems) * st->depth);
270 OPENSSL_free(st->indexes);
271 st->indexes = newitems;
272 st->size = newsize;
273 }
274 st->indexes[(st->depth)++] = idx;
275 return 1;
276 }
277
BN_STACK_pop(BN_STACK * st)278 static unsigned int BN_STACK_pop(BN_STACK *st)
279 {
280 return st->indexes[--(st->depth)];
281 }
282
283 /***********/
284 /* BN_POOL */
285 /***********/
286
BN_POOL_init(BN_POOL * p)287 static void BN_POOL_init(BN_POOL *p)
288 {
289 p->head = p->current = p->tail = NULL;
290 p->used = p->size = 0;
291 }
292
BN_POOL_finish(BN_POOL * p)293 static void BN_POOL_finish(BN_POOL *p)
294 {
295 unsigned int loop;
296 BIGNUM *bn;
297
298 while (p->head) {
299 for (loop = 0, bn = p->head->vals; loop++ < BN_CTX_POOL_SIZE; bn++)
300 if (bn->d)
301 BN_clear_free(bn);
302 p->current = p->head->next;
303 OPENSSL_free(p->head);
304 p->head = p->current;
305 }
306 }
307
308
BN_POOL_get(BN_POOL * p,int flag)309 static BIGNUM *BN_POOL_get(BN_POOL *p, int flag)
310 {
311 BIGNUM *bn;
312 unsigned int loop;
313
314 /* Full; allocate a new pool item and link it in. */
315 if (p->used == p->size) {
316 BN_POOL_ITEM *item;
317
318 if ((item = OPENSSL_malloc(sizeof(*item))) == NULL) {
319 BNerr(BN_F_BN_POOL_GET, ERR_R_MALLOC_FAILURE);
320 return NULL;
321 }
322 for (loop = 0, bn = item->vals; loop++ < BN_CTX_POOL_SIZE; bn++) {
323 bn_init(bn);
324 if ((flag & BN_FLG_SECURE) != 0)
325 BN_set_flags(bn, BN_FLG_SECURE);
326 }
327 item->prev = p->tail;
328 item->next = NULL;
329
330 if (p->head == NULL)
331 p->head = p->current = p->tail = item;
332 else {
333 p->tail->next = item;
334 p->tail = item;
335 p->current = item;
336 }
337 p->size += BN_CTX_POOL_SIZE;
338 p->used++;
339 /* Return the first bignum from the new pool */
340 return item->vals;
341 }
342
343 if (!p->used)
344 p->current = p->head;
345 else if ((p->used % BN_CTX_POOL_SIZE) == 0)
346 p->current = p->current->next;
347 return p->current->vals + ((p->used++) % BN_CTX_POOL_SIZE);
348 }
349
BN_POOL_release(BN_POOL * p,unsigned int num)350 static void BN_POOL_release(BN_POOL *p, unsigned int num)
351 {
352 unsigned int offset = (p->used - 1) % BN_CTX_POOL_SIZE;
353
354 p->used -= num;
355 while (num--) {
356 bn_check_top(p->current->vals + offset);
357 if (offset == 0) {
358 offset = BN_CTX_POOL_SIZE - 1;
359 p->current = p->current->prev;
360 } else
361 offset--;
362 }
363 }
364