crypto/bn/bn_ctx.c

   1 /*
   2  * Copyright 2000-2019 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 #include "internal/cryptlib.h"
  11 #include "bn_lcl.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;
  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
 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
 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
 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
 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
 195 void BN_CTX_end(BN_CTX *ctx)
 196 {
 197     CTXDBG_ENTRY("BN_CTX_end", ctx);
 198     if (ctx->err_stack)
 199         ctx->err_stack--;
 200     else {
 201         unsigned int fp = BN_STACK_pop(&ctx->stack);
 202         /* Does this stack frame have anything to release? */
 203         if (fp < ctx->used)
 204             BN_POOL_release(&ctx->pool, ctx->used - fp);
 205         ctx->used = fp;
 206         /* Unjam "too_many" in case "get" had failed */
 207         ctx->too_many = 0;
 208     }
 209     CTXDBG_EXIT(ctx);
 210 }
 211
 212 BIGNUM *BN_CTX_get(BN_CTX *ctx)
 213 {
 214     BIGNUM *ret;
 215
 216     CTXDBG_ENTRY("BN_CTX_get", ctx);
 217     if (ctx->err_stack || ctx->too_many)
 218         return NULL;
 219     if ((ret = BN_POOL_get(&ctx->pool, ctx->flags)) == NULL) {
 220         /*
 221          * Setting too_many prevents repeated "get" attempts from cluttering
 222          * the error stack.
 223          */
 224         ctx->too_many = 1;
 225         BNerr(BN_F_BN_CTX_GET, BN_R_TOO_MANY_TEMPORARY_VARIABLES);
 226         return NULL;
 227     }
 228     /* OK, make sure the returned bignum is "zero" */
 229     BN_zero(ret);
 230     /* clear BN_FLG_CONSTTIME if leaked from previous frames */
 231     ret->flags &= (~BN_FLG_CONSTTIME);
 232     ctx->used++;
 233     CTXDBG_RET(ctx, ret);
 234     return ret;
 235 }
 236
 237 /************/
 238 /* BN_STACK */
 239 /************/
 240
 241 static void BN_STACK_init(BN_STACK *st)
 242 {
 243     st->indexes = NULL;
 244     st->depth = st->size = 0;
 245 }
 246
 247 static void BN_STACK_finish(BN_STACK *st)
 248 {
 249     OPENSSL_free(st->indexes);
 250     st->indexes = NULL;
 251 }
 252
 253
 254 static int BN_STACK_push(BN_STACK *st, unsigned int idx)
 255 {
 256     if (st->depth == st->size) {
 257         /* Need to expand */
 258         unsigned int newsize =
 259             st->size ? (st->size * 3 / 2) : BN_CTX_START_FRAMES;
 260         unsigned int *newitems;
 261
 262         if ((newitems = OPENSSL_malloc(sizeof(*newitems) * newsize)) == NULL) {
 263             BNerr(BN_F_BN_STACK_PUSH, ERR_R_MALLOC_FAILURE);
 264             return 0;
 265         }
 266         if (st->depth)
 267             memcpy(newitems, st->indexes, sizeof(*newitems) * st->depth);
 268         OPENSSL_free(st->indexes);
 269         st->indexes = newitems;
 270         st->size = newsize;
 271     }
 272     st->indexes[(st->depth)++] = idx;
 273     return 1;
 274 }
 275
 276 static unsigned int BN_STACK_pop(BN_STACK *st)
 277 {
 278     return st->indexes[--(st->depth)];
 279 }
 280
 281 /***********/
 282 /* BN_POOL */
 283 /***********/
 284
 285 static void BN_POOL_init(BN_POOL *p)
 286 {
 287     p->head = p->current = p->tail = NULL;
 288     p->used = p->size = 0;
 289 }
 290
 291 static void BN_POOL_finish(BN_POOL *p)
 292 {
 293     unsigned int loop;
 294     BIGNUM *bn;
 295
 296     while (p->head) {
 297         for (loop = 0, bn = p->head->vals; loop++ < BN_CTX_POOL_SIZE; bn++)
 298             if (bn->d)
 299                 BN_clear_free(bn);
 300         p->current = p->head->next;
 301         OPENSSL_free(p->head);
 302         p->head = p->current;
 303     }
 304 }
 305
 306
 307 static BIGNUM *BN_POOL_get(BN_POOL *p, int flag)
 308 {
 309     BIGNUM *bn;
 310     unsigned int loop;
 311
 312     /* Full; allocate a new pool item and link it in. */
 313     if (p->used == p->size) {
 314         BN_POOL_ITEM *item;
 315
 316         if ((item = OPENSSL_malloc(sizeof(*item))) == NULL) {
 317             BNerr(BN_F_BN_POOL_GET, ERR_R_MALLOC_FAILURE);
 318             return NULL;
 319         }
 320         for (loop = 0, bn = item->vals; loop++ < BN_CTX_POOL_SIZE; bn++) {
 321             bn_init(bn);
 322             if ((flag & BN_FLG_SECURE) != 0)
 323                 BN_set_flags(bn, BN_FLG_SECURE);
 324         }
 325         item->prev = p->tail;
 326         item->next = NULL;
 327
 328         if (p->head == NULL)
 329             p->head = p->current = p->tail = item;
 330         else {
 331             p->tail->next = item;
 332             p->tail = item;
 333             p->current = item;
 334         }
 335         p->size += BN_CTX_POOL_SIZE;
 336         p->used++;
 337         /* Return the first bignum from the new pool */
 338         return item->vals;
 339     }
 340
 341     if (!p->used)
 342         p->current = p->head;
 343     else if ((p->used % BN_CTX_POOL_SIZE) == 0)
 344         p->current = p->current->next;
 345     return p->current->vals + ((p->used++) % BN_CTX_POOL_SIZE);
 346 }
 347
 348 static void BN_POOL_release(BN_POOL *p, unsigned int num)
 349 {
 350     unsigned int offset = (p->used - 1) % BN_CTX_POOL_SIZE;
 351
 352     p->used -= num;
 353     while (num--) {
 354         bn_check_top(p->current->vals + offset);
 355         if (offset == 0) {
 356             offset = BN_CTX_POOL_SIZE - 1;
 357             p->current = p->current->prev;
 358         } else
 359             offset--;
 360     }
 361 }