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 <openssl/trace.h>
  11 #include "internal/cryptlib.h"
  12 #include "bn_local.h"
  13
  14 /*-
  15  * TODO list
  16  *
  17  * 1. Check a bunch of "(words+1)" type hacks in various bignum functions and
  18  * check they can be safely removed.
  19  *  - Check +1 and other ugliness in BN_from_montgomery()
  20  *
  21  * 2. Consider allowing a BN_new_ex() that, at least, lets you specify an
  22  * appropriate 'block' size that will be honoured by bn_expand_internal() to
  23  * prevent piddly little reallocations. OTOH, profiling bignum expansions in
  24  * BN_CTX doesn't show this to be a big issue.
  25  */
  26
  27 /* How many bignums are in each "pool item"; */
  28 #define BN_CTX_POOL_SIZE        16
  29 /* The stack frame info is resizing, set a first-time expansion size; */
  30 #define BN_CTX_START_FRAMES     32
  31
  32 /***********/
  33 /* BN_POOL */
  34 /***********/
  35
  36 /* A bundle of bignums that can be linked with other bundles */
  37 typedef struct bignum_pool_item {
  38     /* The bignum values */
  39     BIGNUM vals[BN_CTX_POOL_SIZE];
  40     /* Linked-list admin */
  41     struct bignum_pool_item *prev, *next;
  42 } BN_POOL_ITEM;
  43 /* A linked-list of bignums grouped in bundles */
  44 typedef struct bignum_pool {
  45     /* Linked-list admin */
  46     BN_POOL_ITEM *head, *current, *tail;
  47     /* Stack depth and allocation size */
  48     unsigned used, size;
  49 } BN_POOL;
  50 static void BN_POOL_init(BN_POOL *);
  51 static void BN_POOL_finish(BN_POOL *);
  52 static BIGNUM *BN_POOL_get(BN_POOL *, int);
  53 static void BN_POOL_release(BN_POOL *, unsigned int);
  54
  55 /************/
  56 /* BN_STACK */
  57 /************/
  58
  59 /* A wrapper to manage the "stack frames" */
  60 typedef struct bignum_ctx_stack {
  61     /* Array of indexes into the bignum stack */
  62     unsigned int *indexes;
  63     /* Number of stack frames, and the size of the allocated array */
  64     unsigned int depth, size;
  65 } BN_STACK;
  66 static void BN_STACK_init(BN_STACK *);
  67 static void BN_STACK_finish(BN_STACK *);
  68 static int BN_STACK_push(BN_STACK *, unsigned int);
  69 static unsigned int BN_STACK_pop(BN_STACK *);
  70
  71 /**********/
  72 /* BN_CTX */
  73 /**********/
  74
  75 /* The opaque BN_CTX type */
  76 struct bignum_ctx {
  77     /* The bignum bundles */
  78     BN_POOL pool;
  79     /* The "stack frames", if you will */
  80     BN_STACK stack;
  81     /* The number of bignums currently assigned */
  82     unsigned int used;
  83     /* Depth of stack overflow */
  84     int err_stack;
  85     /* Block "gets" until an "end" (compatibility behaviour) */
  86     int too_many;
  87     /* Flags. */
  88     int flags;
  89     /* The library context */
  90     OPENSSL_CTX *libctx;
  91 };
  92
  93 #ifndef FIPS_MODE
  94 /* Debugging functionality */
  95 static void ctxdbg(BIO *channel, const char *text, BN_CTX *ctx)
  96 {
  97     unsigned int bnidx = 0, fpidx = 0;
  98     BN_POOL_ITEM *item = ctx->pool.head;
  99     BN_STACK *stack = &ctx->stack;
 100
 101     BIO_printf(channel, "%s\n", text);
 102     BIO_printf(channel, "  (%16p): ", (void*)ctx);
 103     while (bnidx < ctx->used) {
 104         BIO_printf(channel, "%03x ",
 105                    item->vals[bnidx++ % BN_CTX_POOL_SIZE].dmax);
 106         if (!(bnidx % BN_CTX_POOL_SIZE))
 107             item = item->next;
 108     }
 109     BIO_printf(channel, "\n");
 110     bnidx = 0;
 111     BIO_printf(channel, "   %16s : ", "");
 112     while (fpidx < stack->depth) {
 113         while (bnidx++ < stack->indexes[fpidx])
 114             BIO_printf(channel, "    ");
 115         BIO_printf(channel, "^^^ ");
 116         bnidx++;
 117         fpidx++;
 118     }
 119     BIO_printf(channel, "\n");
 120 }
 121
 122 # define CTXDBG(str, ctx)           \
 123     OSSL_TRACE_BEGIN(BN_CTX) {      \
 124         ctxdbg(trc_out, str, ctx);  \
 125     } OSSL_TRACE_END(BN_CTX)
 126 #else
 127 /* TODO(3.0): Consider if we want to do this in FIPS mode */
 128 # define CTXDBG(str, ctx) do {} while(0)
 129 #endif /* FIPS_MODE */
 130
 131 BN_CTX *BN_CTX_new_ex(OPENSSL_CTX *ctx)
 132 {
 133     BN_CTX *ret;
 134
 135     if ((ret = OPENSSL_zalloc(sizeof(*ret))) == NULL) {
 136         BNerr(BN_F_BN_CTX_NEW_EX, ERR_R_MALLOC_FAILURE);
 137         return NULL;
 138     }
 139     /* Initialise the structure */
 140     BN_POOL_init(&ret->pool);
 141     BN_STACK_init(&ret->stack);
 142     ret->libctx = ctx;
 143     return ret;
 144 }
 145
 146 #ifndef FIPS_MODE
 147 BN_CTX *BN_CTX_new(void)
 148 {
 149     return BN_CTX_new_ex(NULL);
 150 }
 151 #endif
 152
 153 BN_CTX *BN_CTX_secure_new_ex(OPENSSL_CTX *ctx)
 154 {
 155     BN_CTX *ret = BN_CTX_new_ex(ctx);
 156
 157     if (ret != NULL)
 158         ret->flags = BN_FLG_SECURE;
 159     return ret;
 160 }
 161
 162 #ifndef FIPS_MODE
 163 BN_CTX *BN_CTX_secure_new(void)
 164 {
 165     return BN_CTX_secure_new_ex(NULL);
 166 }
 167 #endif
 168
 169 void BN_CTX_free(BN_CTX *ctx)
 170 {
 171     if (ctx == NULL)
 172         return;
 173 #ifndef FIPS_MODE
 174     OSSL_TRACE_BEGIN(BN_CTX) {
 175         BN_POOL_ITEM *pool = ctx->pool.head;
 176         BIO_printf(trc_out,
 177                    "BN_CTX_free(): stack-size=%d, pool-bignums=%d\n",
 178                    ctx->stack.size, ctx->pool.size);
 179         BIO_printf(trc_out, "  dmaxs: ");
 180         while (pool) {
 181             unsigned loop = 0;
 182             while (loop < BN_CTX_POOL_SIZE)
 183                 BIO_printf(trc_out, "%02x ", pool->vals[loop++].dmax);
 184             pool = pool->next;
 185         }
 186         BIO_printf(trc_out, "\n");
 187     } OSSL_TRACE_END(BN_CTX);
 188 #endif
 189     BN_STACK_finish(&ctx->stack);
 190     BN_POOL_finish(&ctx->pool);
 191     OPENSSL_free(ctx);
 192 }
 193
 194 void BN_CTX_start(BN_CTX *ctx)
 195 {
 196     CTXDBG("ENTER BN_CTX_start()", ctx);
 197     /* If we're already overflowing ... */
 198     if (ctx->err_stack || ctx->too_many)
 199         ctx->err_stack++;
 200     /* (Try to) get a new frame pointer */
 201     else if (!BN_STACK_push(&ctx->stack, ctx->used)) {
 202         BNerr(BN_F_BN_CTX_START, BN_R_TOO_MANY_TEMPORARY_VARIABLES);
 203         ctx->err_stack++;
 204     }
 205     CTXDBG("LEAVE BN_CTX_start()", ctx);
 206 }
 207
 208 void BN_CTX_end(BN_CTX *ctx)
 209 {
 210     if (ctx == NULL)
 211         return;
 212     CTXDBG("ENTER BN_CTX_end()", ctx);
 213     if (ctx->err_stack)
 214         ctx->err_stack--;
 215     else {
 216         unsigned int fp = BN_STACK_pop(&ctx->stack);
 217         /* Does this stack frame have anything to release? */
 218         if (fp < ctx->used)
 219             BN_POOL_release(&ctx->pool, ctx->used - fp);
 220         ctx->used = fp;
 221         /* Unjam "too_many" in case "get" had failed */
 222         ctx->too_many = 0;
 223     }
 224     CTXDBG("LEAVE BN_CTX_end()", ctx);
 225 }
 226
 227 BIGNUM *BN_CTX_get(BN_CTX *ctx)
 228 {
 229     BIGNUM *ret;
 230
 231     CTXDBG("ENTER BN_CTX_get()", ctx);
 232     if (ctx->err_stack || ctx->too_many)
 233         return NULL;
 234     if ((ret = BN_POOL_get(&ctx->pool, ctx->flags)) == NULL) {
 235         /*
 236          * Setting too_many prevents repeated "get" attempts from cluttering
 237          * the error stack.
 238          */
 239         ctx->too_many = 1;
 240         BNerr(BN_F_BN_CTX_GET, BN_R_TOO_MANY_TEMPORARY_VARIABLES);
 241         return NULL;
 242     }
 243     /* OK, make sure the returned bignum is "zero" */
 244     BN_zero(ret);
 245     /* clear BN_FLG_CONSTTIME if leaked from previous frames */
 246     ret->flags &= (~BN_FLG_CONSTTIME);
 247     ctx->used++;
 248     CTXDBG("LEAVE BN_CTX_get()", ctx);
 249     return ret;
 250 }
 251
 252 OPENSSL_CTX *bn_get_lib_ctx(BN_CTX *ctx)
 253 {
 254     if (ctx == NULL)
 255         return NULL;
 256     return ctx->libctx;
 257 }
 258
 259 /************/
 260 /* BN_STACK */
 261 /************/
 262
 263 static void BN_STACK_init(BN_STACK *st)
 264 {
 265     st->indexes = NULL;
 266     st->depth = st->size = 0;
 267 }
 268
 269 static void BN_STACK_finish(BN_STACK *st)
 270 {
 271     OPENSSL_free(st->indexes);
 272     st->indexes = NULL;
 273 }
 274
 275
 276 static int BN_STACK_push(BN_STACK *st, unsigned int idx)
 277 {
 278     if (st->depth == st->size) {
 279         /* Need to expand */
 280         unsigned int newsize =
 281             st->size ? (st->size * 3 / 2) : BN_CTX_START_FRAMES;
 282         unsigned int *newitems;
 283
 284         if ((newitems = OPENSSL_malloc(sizeof(*newitems) * newsize)) == NULL) {
 285             BNerr(BN_F_BN_STACK_PUSH, ERR_R_MALLOC_FAILURE);
 286             return 0;
 287         }
 288         if (st->depth)
 289             memcpy(newitems, st->indexes, sizeof(*newitems) * st->depth);
 290         OPENSSL_free(st->indexes);
 291         st->indexes = newitems;
 292         st->size = newsize;
 293     }
 294     st->indexes[(st->depth)++] = idx;
 295     return 1;
 296 }
 297
 298 static unsigned int BN_STACK_pop(BN_STACK *st)
 299 {
 300     return st->indexes[--(st->depth)];
 301 }
 302
 303 /***********/
 304 /* BN_POOL */
 305 /***********/
 306
 307 static void BN_POOL_init(BN_POOL *p)
 308 {
 309     p->head = p->current = p->tail = NULL;
 310     p->used = p->size = 0;
 311 }
 312
 313 static void BN_POOL_finish(BN_POOL *p)
 314 {
 315     unsigned int loop;
 316     BIGNUM *bn;
 317
 318     while (p->head) {
 319         for (loop = 0, bn = p->head->vals; loop++ < BN_CTX_POOL_SIZE; bn++)
 320             if (bn->d)
 321                 BN_clear_free(bn);
 322         p->current = p->head->next;
 323         OPENSSL_free(p->head);
 324         p->head = p->current;
 325     }
 326 }
 327
 328
 329 static BIGNUM *BN_POOL_get(BN_POOL *p, int flag)
 330 {
 331     BIGNUM *bn;
 332     unsigned int loop;
 333
 334     /* Full; allocate a new pool item and link it in. */
 335     if (p->used == p->size) {
 336         BN_POOL_ITEM *item;
 337
 338         if ((item = OPENSSL_malloc(sizeof(*item))) == NULL) {
 339             BNerr(BN_F_BN_POOL_GET, ERR_R_MALLOC_FAILURE);
 340             return NULL;
 341         }
 342         for (loop = 0, bn = item->vals; loop++ < BN_CTX_POOL_SIZE; bn++) {
 343             bn_init(bn);
 344             if ((flag & BN_FLG_SECURE) != 0)
 345                 BN_set_flags(bn, BN_FLG_SECURE);
 346         }
 347         item->prev = p->tail;
 348         item->next = NULL;
 349
 350         if (p->head == NULL)
 351             p->head = p->current = p->tail = item;
 352         else {
 353             p->tail->next = item;
 354             p->tail = item;
 355             p->current = item;
 356         }
 357         p->size += BN_CTX_POOL_SIZE;
 358         p->used++;
 359         /* Return the first bignum from the new pool */
 360         return item->vals;
 361     }
 362
 363     if (!p->used)
 364         p->current = p->head;
 365     else if ((p->used % BN_CTX_POOL_SIZE) == 0)
 366         p->current = p->current->next;
 367     return p->current->vals + ((p->used++) % BN_CTX_POOL_SIZE);
 368 }
 369
 370 static void BN_POOL_release(BN_POOL *p, unsigned int num)
 371 {
 372     unsigned int offset = (p->used - 1) % BN_CTX_POOL_SIZE;
 373
 374     p->used -= num;
 375     while (num--) {
 376         bn_check_top(p->current->vals + offset);
 377         if (offset == 0) {
 378             offset = BN_CTX_POOL_SIZE - 1;
 379             p->current = p->current->prev;
 380         } else
 381             offset--;
 382     }
 383 }