crypto/bn/bn_ctx.c

   1 /*
   2  * Copyright 2000-2021 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 #include <openssl/trace.h>
  11 #include "internal/cryptlib.h"
  12 #include "bn_local.h"
  13
  14 /* How many bignums are in each "pool item"; */
  15 #define BN_CTX_POOL_SIZE        16
  16 /* The stack frame info is resizing, set a first-time expansion size; */
  17 #define BN_CTX_START_FRAMES     32
  18
  19 /***********/
  20 /* BN_POOL */
  21 /***********/
  22
  23 /* A bundle of bignums that can be linked with other bundles */
  24 typedef struct bignum_pool_item {
  25     /* The bignum values */
  26     BIGNUM vals[BN_CTX_POOL_SIZE];
  27     /* Linked-list admin */
  28     struct bignum_pool_item *prev, *next;
  29 } BN_POOL_ITEM;
  30 /* A linked-list of bignums grouped in bundles */
  31 typedef struct bignum_pool {
  32     /* Linked-list admin */
  33     BN_POOL_ITEM *head, *current, *tail;
  34     /* Stack depth and allocation size */
  35     unsigned used, size;
  36 } BN_POOL;
  37 static void BN_POOL_init(BN_POOL *);
  38 static void BN_POOL_finish(BN_POOL *);
  39 static BIGNUM *BN_POOL_get(BN_POOL *, int);
  40 static void BN_POOL_release(BN_POOL *, unsigned int);
  41
  42 /************/
  43 /* BN_STACK */
  44 /************/
  45
  46 /* A wrapper to manage the "stack frames" */
  47 typedef struct bignum_ctx_stack {
  48     /* Array of indexes into the bignum stack */
  49     unsigned int *indexes;
  50     /* Number of stack frames, and the size of the allocated array */
  51     unsigned int depth, size;
  52 } BN_STACK;
  53 static void BN_STACK_init(BN_STACK *);
  54 static void BN_STACK_finish(BN_STACK *);
  55 static int BN_STACK_push(BN_STACK *, unsigned int);
  56 static unsigned int BN_STACK_pop(BN_STACK *);
  57
  58 /**********/
  59 /* BN_CTX */
  60 /**********/
  61
  62 /* The opaque BN_CTX type */
  63 struct bignum_ctx {
  64     /* The bignum bundles */
  65     BN_POOL pool;
  66     /* The "stack frames", if you will */
  67     BN_STACK stack;
  68     /* The number of bignums currently assigned */
  69     unsigned int used;
  70     /* Depth of stack overflow */
  71     int err_stack;
  72     /* Block "gets" until an "end" (compatibility behaviour) */
  73     int too_many;
  74     /* Flags. */
  75     int flags;
  76     /* The library context */
  77     OSSL_LIB_CTX *libctx;
  78 };
  79
  80 #ifndef FIPS_MODULE
  81 /* Debugging functionality */
  82 static void ctxdbg(BIO *channel, const char *text, BN_CTX *ctx)
  83 {
  84     unsigned int bnidx = 0, fpidx = 0;
  85     BN_POOL_ITEM *item = ctx->pool.head;
  86     BN_STACK *stack = &ctx->stack;
  87
  88     BIO_printf(channel, "%s\n", text);
  89     BIO_printf(channel, "  (%16p): ", (void*)ctx);
  90     while (bnidx < ctx->used) {
  91         BIO_printf(channel, "%03x ",
  92                    item->vals[bnidx++ % BN_CTX_POOL_SIZE].dmax);
  93         if (!(bnidx % BN_CTX_POOL_SIZE))
  94             item = item->next;
  95     }
  96     BIO_printf(channel, "\n");
  97     bnidx = 0;
  98     BIO_printf(channel, "   %16s : ", "");
  99     while (fpidx < stack->depth) {
 100         while (bnidx++ < stack->indexes[fpidx])
 101             BIO_printf(channel, "    ");
 102         BIO_printf(channel, "^^^ ");
 103         bnidx++;
 104         fpidx++;
 105     }
 106     BIO_printf(channel, "\n");
 107 }
 108
 109 # define CTXDBG(str, ctx)           \
 110     OSSL_TRACE_BEGIN(BN_CTX) {      \
 111         ctxdbg(trc_out, str, ctx);  \
 112     } OSSL_TRACE_END(BN_CTX)
 113 #else
 114 /* We do not want tracing in FIPS module */
 115 # define CTXDBG(str, ctx) do {} while(0)
 116 #endif /* FIPS_MODULE */
 117
 118 BN_CTX *BN_CTX_new_ex(OSSL_LIB_CTX *ctx)
 119 {
 120     BN_CTX *ret;
 121
 122     if ((ret = OPENSSL_zalloc(sizeof(*ret))) == NULL)
 123         return NULL;
 124     /* Initialise the structure */
 125     BN_POOL_init(&ret->pool);
 126     BN_STACK_init(&ret->stack);
 127     ret->libctx = ctx;
 128     return ret;
 129 }
 130
 131 #ifndef FIPS_MODULE
 132 BN_CTX *BN_CTX_new(void)
 133 {
 134     return BN_CTX_new_ex(NULL);
 135 }
 136 #endif
 137
 138 BN_CTX *BN_CTX_secure_new_ex(OSSL_LIB_CTX *ctx)
 139 {
 140     BN_CTX *ret = BN_CTX_new_ex(ctx);
 141
 142     if (ret != NULL)
 143         ret->flags = BN_FLG_SECURE;
 144     return ret;
 145 }
 146
 147 #ifndef FIPS_MODULE
 148 BN_CTX *BN_CTX_secure_new(void)
 149 {
 150     return BN_CTX_secure_new_ex(NULL);
 151 }
 152 #endif
 153
 154 void BN_CTX_free(BN_CTX *ctx)
 155 {
 156     if (ctx == NULL)
 157         return;
 158 #ifndef FIPS_MODULE
 159     OSSL_TRACE_BEGIN(BN_CTX) {
 160         BN_POOL_ITEM *pool = ctx->pool.head;
 161         BIO_printf(trc_out,
 162                    "BN_CTX_free(): stack-size=%d, pool-bignums=%d\n",
 163                    ctx->stack.size, ctx->pool.size);
 164         BIO_printf(trc_out, "  dmaxs: ");
 165         while (pool) {
 166             unsigned loop = 0;
 167             while (loop < BN_CTX_POOL_SIZE)
 168                 BIO_printf(trc_out, "%02x ", pool->vals[loop++].dmax);
 169             pool = pool->next;
 170         }
 171         BIO_printf(trc_out, "\n");
 172     } OSSL_TRACE_END(BN_CTX);
 173 #endif
 174     BN_STACK_finish(&ctx->stack);
 175     BN_POOL_finish(&ctx->pool);
 176     OPENSSL_free(ctx);
 177 }
 178
 179 void BN_CTX_start(BN_CTX *ctx)
 180 {
 181     CTXDBG("ENTER BN_CTX_start()", ctx);
 182     /* If we're already overflowing ... */
 183     if (ctx->err_stack || ctx->too_many)
 184         ctx->err_stack++;
 185     /* (Try to) get a new frame pointer */
 186     else if (!BN_STACK_push(&ctx->stack, ctx->used)) {
 187         ERR_raise(ERR_LIB_BN, BN_R_TOO_MANY_TEMPORARY_VARIABLES);
 188         ctx->err_stack++;
 189     }
 190     CTXDBG("LEAVE BN_CTX_start()", ctx);
 191 }
 192
 193 void BN_CTX_end(BN_CTX *ctx)
 194 {
 195     if (ctx == NULL)
 196         return;
 197     CTXDBG("ENTER 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("LEAVE BN_CTX_end()", ctx);
 210 }
 211
 212 BIGNUM *BN_CTX_get(BN_CTX *ctx)
 213 {
 214     BIGNUM *ret;
 215
 216     CTXDBG("ENTER 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         ERR_raise(ERR_LIB_BN, 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("LEAVE BN_CTX_get()", ctx);
 234     return ret;
 235 }
 236
 237 OSSL_LIB_CTX *ossl_bn_get_libctx(BN_CTX *ctx)
 238 {
 239     if (ctx == NULL)
 240         return NULL;
 241     return ctx->libctx;
 242 }
 243
 244 /************/
 245 /* BN_STACK */
 246 /************/
 247
 248 static void BN_STACK_init(BN_STACK *st)
 249 {
 250     st->indexes = NULL;
 251     st->depth = st->size = 0;
 252 }
 253
 254 static void BN_STACK_finish(BN_STACK *st)
 255 {
 256     OPENSSL_free(st->indexes);
 257     st->indexes = NULL;
 258 }
 259
 260
 261 static int BN_STACK_push(BN_STACK *st, unsigned int idx)
 262 {
 263     if (st->depth == st->size) {
 264         /* Need to expand */
 265         unsigned int newsize =
 266             st->size ? (st->size * 3 / 2) : BN_CTX_START_FRAMES;
 267         unsigned int *newitems;
 268
 269         if ((newitems = OPENSSL_malloc(sizeof(*newitems) * newsize)) == NULL)
 270             return 0;
 271         if (st->depth)
 272             memcpy(newitems, st->indexes, sizeof(*newitems) * st->depth);
 273         OPENSSL_free(st->indexes);
 274         st->indexes = newitems;
 275         st->size = newsize;
 276     }
 277     st->indexes[(st->depth)++] = idx;
 278     return 1;
 279 }
 280
 281 static unsigned int BN_STACK_pop(BN_STACK *st)
 282 {
 283     return st->indexes[--(st->depth)];
 284 }
 285
 286 /***********/
 287 /* BN_POOL */
 288 /***********/
 289
 290 static void BN_POOL_init(BN_POOL *p)
 291 {
 292     p->head = p->current = p->tail = NULL;
 293     p->used = p->size = 0;
 294 }
 295
 296 static void BN_POOL_finish(BN_POOL *p)
 297 {
 298     unsigned int loop;
 299     BIGNUM *bn;
 300
 301     while (p->head) {
 302         for (loop = 0, bn = p->head->vals; loop++ < BN_CTX_POOL_SIZE; bn++)
 303             if (bn->d)
 304                 BN_clear_free(bn);
 305         p->current = p->head->next;
 306         OPENSSL_free(p->head);
 307         p->head = p->current;
 308     }
 309 }
 310
 311
 312 static BIGNUM *BN_POOL_get(BN_POOL *p, int flag)
 313 {
 314     BIGNUM *bn;
 315     unsigned int loop;
 316
 317     /* Full; allocate a new pool item and link it in. */
 318     if (p->used == p->size) {
 319         BN_POOL_ITEM *item;
 320
 321         if ((item = OPENSSL_malloc(sizeof(*item))) == NULL)
 322             return NULL;
 323         for (loop = 0, bn = item->vals; loop++ < BN_CTX_POOL_SIZE; bn++) {
 324             bn_init(bn);
 325             if ((flag & BN_FLG_SECURE) != 0)
 326                 BN_set_flags(bn, BN_FLG_SECURE);
 327         }
 328         item->prev = p->tail;
 329         item->next = NULL;
 330
 331         if (p->head == NULL)
 332             p->head = p->current = p->tail = item;
 333         else {
 334             p->tail->next = item;
 335             p->tail = item;
 336             p->current = item;
 337         }
 338         p->size += BN_CTX_POOL_SIZE;
 339         p->used++;
 340         /* Return the first bignum from the new pool */
 341         return item->vals;
 342     }
 343
 344     if (!p->used)
 345         p->current = p->head;
 346     else if ((p->used % BN_CTX_POOL_SIZE) == 0)
 347         p->current = p->current->next;
 348     return p->current->vals + ((p->used++) % BN_CTX_POOL_SIZE);
 349 }
 350
 351 static void BN_POOL_release(BN_POOL *p, unsigned int num)
 352 {
 353     unsigned int offset = (p->used - 1) % BN_CTX_POOL_SIZE;
 354
 355     p->used -= num;
 356     while (num--) {
 357         bn_check_top(p->current->vals + offset);
 358         if (offset == 0) {
 359             offset = BN_CTX_POOL_SIZE - 1;
 360             p->current = p->current->prev;
 361         } else
 362             offset--;
 363     }
 364 }