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 */
24typedef 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 */
31typedef 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;
37static void BN_POOL_init(BN_POOL *);
38static void BN_POOL_finish(BN_POOL *);
39static BIGNUM *BN_POOL_get(BN_POOL *, int);
40static void BN_POOL_release(BN_POOL *, unsigned int);
41
42/************/
43/* BN_STACK */
44/************/
45
46/* A wrapper to manage the "stack frames" */
47typedef 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;
53static void BN_STACK_init(BN_STACK *);
54static void BN_STACK_finish(BN_STACK *);
55static int BN_STACK_push(BN_STACK *, unsigned int);
56static unsigned int BN_STACK_pop(BN_STACK *);
57
58/**********/
59/* BN_CTX */
60/**********/
61
62/* The opaque BN_CTX type */
63struct 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 */
82static 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
118BN_CTX *BN_CTX_new_ex(OSSL_LIB_CTX *ctx)
119{
120    BN_CTX *ret;
121
122    if ((ret = OPENSSL_zalloc(sizeof(*ret))) == NULL) {
123        ERR_raise(ERR_LIB_BN, ERR_R_MALLOC_FAILURE);
124        return NULL;
125    }
126    /* Initialise the structure */
127    BN_POOL_init(&ret->pool);
128    BN_STACK_init(&ret->stack);
129    ret->libctx = ctx;
130    return ret;
131}
132
133#ifndef FIPS_MODULE
134BN_CTX *BN_CTX_new(void)
135{
136    return BN_CTX_new_ex(NULL);
137}
138#endif
139
140BN_CTX *BN_CTX_secure_new_ex(OSSL_LIB_CTX *ctx)
141{
142    BN_CTX *ret = BN_CTX_new_ex(ctx);
143
144    if (ret != NULL)
145        ret->flags = BN_FLG_SECURE;
146    return ret;
147}
148
149#ifndef FIPS_MODULE
150BN_CTX *BN_CTX_secure_new(void)
151{
152    return BN_CTX_secure_new_ex(NULL);
153}
154#endif
155
156void BN_CTX_free(BN_CTX *ctx)
157{
158    if (ctx == NULL)
159        return;
160#ifndef FIPS_MODULE
161    OSSL_TRACE_BEGIN(BN_CTX) {
162        BN_POOL_ITEM *pool = ctx->pool.head;
163        BIO_printf(trc_out,
164                   "BN_CTX_free(): stack-size=%d, pool-bignums=%d\n",
165                   ctx->stack.size, ctx->pool.size);
166        BIO_printf(trc_out, "  dmaxs: ");
167        while (pool) {
168            unsigned loop = 0;
169            while (loop < BN_CTX_POOL_SIZE)
170                BIO_printf(trc_out, "%02x ", pool->vals[loop++].dmax);
171            pool = pool->next;
172        }
173        BIO_printf(trc_out, "\n");
174    } OSSL_TRACE_END(BN_CTX);
175#endif
176    BN_STACK_finish(&ctx->stack);
177    BN_POOL_finish(&ctx->pool);
178    OPENSSL_free(ctx);
179}
180
181void BN_CTX_start(BN_CTX *ctx)
182{
183    CTXDBG("ENTER 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        ERR_raise(ERR_LIB_BN, BN_R_TOO_MANY_TEMPORARY_VARIABLES);
190        ctx->err_stack++;
191    }
192    CTXDBG("LEAVE BN_CTX_start()", ctx);
193}
194
195void BN_CTX_end(BN_CTX *ctx)
196{
197    if (ctx == NULL)
198        return;
199    CTXDBG("ENTER 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("LEAVE BN_CTX_end()", ctx);
212}
213
214BIGNUM *BN_CTX_get(BN_CTX *ctx)
215{
216    BIGNUM *ret;
217
218    CTXDBG("ENTER 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        ERR_raise(ERR_LIB_BN, 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("LEAVE BN_CTX_get()", ctx);
236    return ret;
237}
238
239OSSL_LIB_CTX *ossl_bn_get_libctx(BN_CTX *ctx)
240{
241    if (ctx == NULL)
242        return NULL;
243    return ctx->libctx;
244}
245
246/************/
247/* BN_STACK */
248/************/
249
250static void BN_STACK_init(BN_STACK *st)
251{
252    st->indexes = NULL;
253    st->depth = st->size = 0;
254}
255
256static void BN_STACK_finish(BN_STACK *st)
257{
258    OPENSSL_free(st->indexes);
259    st->indexes = NULL;
260}
261
262
263static int BN_STACK_push(BN_STACK *st, unsigned int idx)
264{
265    if (st->depth == st->size) {
266        /* Need to expand */
267        unsigned int newsize =
268            st->size ? (st->size * 3 / 2) : BN_CTX_START_FRAMES;
269        unsigned int *newitems;
270
271        if ((newitems = OPENSSL_malloc(sizeof(*newitems) * newsize)) == NULL) {
272            ERR_raise(ERR_LIB_BN, ERR_R_MALLOC_FAILURE);
273            return 0;
274        }
275        if (st->depth)
276            memcpy(newitems, st->indexes, sizeof(*newitems) * st->depth);
277        OPENSSL_free(st->indexes);
278        st->indexes = newitems;
279        st->size = newsize;
280    }
281    st->indexes[(st->depth)++] = idx;
282    return 1;
283}
284
285static unsigned int BN_STACK_pop(BN_STACK *st)
286{
287    return st->indexes[--(st->depth)];
288}
289
290/***********/
291/* BN_POOL */
292/***********/
293
294static void BN_POOL_init(BN_POOL *p)
295{
296    p->head = p->current = p->tail = NULL;
297    p->used = p->size = 0;
298}
299
300static void BN_POOL_finish(BN_POOL *p)
301{
302    unsigned int loop;
303    BIGNUM *bn;
304
305    while (p->head) {
306        for (loop = 0, bn = p->head->vals; loop++ < BN_CTX_POOL_SIZE; bn++)
307            if (bn->d)
308                BN_clear_free(bn);
309        p->current = p->head->next;
310        OPENSSL_free(p->head);
311        p->head = p->current;
312    }
313}
314
315
316static BIGNUM *BN_POOL_get(BN_POOL *p, int flag)
317{
318    BIGNUM *bn;
319    unsigned int loop;
320
321    /* Full; allocate a new pool item and link it in. */
322    if (p->used == p->size) {
323        BN_POOL_ITEM *item;
324
325        if ((item = OPENSSL_malloc(sizeof(*item))) == NULL) {
326            ERR_raise(ERR_LIB_BN, ERR_R_MALLOC_FAILURE);
327            return NULL;
328        }
329        for (loop = 0, bn = item->vals; loop++ < BN_CTX_POOL_SIZE; bn++) {
330            bn_init(bn);
331            if ((flag & BN_FLG_SECURE) != 0)
332                BN_set_flags(bn, BN_FLG_SECURE);
333        }
334        item->prev = p->tail;
335        item->next = NULL;
336
337        if (p->head == NULL)
338            p->head = p->current = p->tail = item;
339        else {
340            p->tail->next = item;
341            p->tail = item;
342            p->current = item;
343        }
344        p->size += BN_CTX_POOL_SIZE;
345        p->used++;
346        /* Return the first bignum from the new pool */
347        return item->vals;
348    }
349
350    if (!p->used)
351        p->current = p->head;
352    else if ((p->used % BN_CTX_POOL_SIZE) == 0)
353        p->current = p->current->next;
354    return p->current->vals + ((p->used++) % BN_CTX_POOL_SIZE);
355}
356
357static void BN_POOL_release(BN_POOL *p, unsigned int num)
358{
359    unsigned int offset = (p->used - 1) % BN_CTX_POOL_SIZE;
360
361    p->used -= num;
362    while (num--) {
363        bn_check_top(p->current->vals + offset);
364        if (offset == 0) {
365            offset = BN_CTX_POOL_SIZE - 1;
366            p->current = p->current->prev;
367        } else
368            offset--;
369    }
370}
371