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FP SmallStack Fix
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The function _fp_exptmod_nct() is using WOLFSSL_NO_MALLOC to guard
using stack allocation vs malloc. It's twin function _fp_exptmod_ct()
is using WOLFSSL_SMALL_STACK for this. This is causing inappropriate use
of malloc() in a small stack environment. The no-malloc case will also
be kept so static memory and no-malloc fix still works.

1. Change the guards for `#ifndef WOLFSSL_NO_MALLOC` in the function
   `_fp_exptmod_nct()` to `#if defined(WOLFSSL_SMALL_STACK) &&
   !defined(WOLFSSL_NO_MALLOC)`.
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@ejohnstown
ejohnstown committed Sep 17, 2024
1 parent 5ef617a commit 47e5140
Showing 1 changed file with 20 additions and 20 deletions.
40 changes: 20 additions & 20 deletions wolfcrypt/src/tfm.c
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Original file line number Diff line number Diff line change
Expand Up @@ -2430,7 +2430,7 @@ static int _fp_exptmod_nct(fp_int * G, fp_int * X, fp_int * P, fp_int * Y)
fp_int *res;
fp_digit buf, mp;
int err, bitbuf, bitcpy, bitcnt, mode, digidx, x, y, winsize;
#ifndef WOLFSSL_NO_MALLOC
#if defined(WOLFSSL_SMALL_STACK) && !defined(WOLFSSL_NO_MALLOC)
fp_int *M;
#else
fp_int M[(1 << 6) + 1];
Expand All @@ -2455,7 +2455,7 @@ static int _fp_exptmod_nct(fp_int * G, fp_int * X, fp_int * P, fp_int * Y)
return err;
}

#ifndef WOLFSSL_NO_MALLOC
#if defined(WOLFSSL_SMALL_STACK) && !defined(WOLFSSL_NO_MALLOC)
/* only allocate space for what's needed for window plus res */
M = (fp_int*)XMALLOC(sizeof(fp_int)*((1 << winsize) + 1), NULL,
DYNAMIC_TYPE_BIGINT);
Expand All @@ -2482,7 +2482,7 @@ static int _fp_exptmod_nct(fp_int * G, fp_int * X, fp_int * P, fp_int * Y)
/* now we need R mod m */
err = fp_montgomery_calc_normalization (res, P);
if (err != FP_OKAY) {
#ifndef WOLFSSL_NO_MALLOC
#if defined(WOLFSSL_SMALL_STACK) && !defined(WOLFSSL_NO_MALLOC)
XFREE(M, NULL, DYNAMIC_TYPE_BIGINT);
#endif
return err;
Expand All @@ -2493,7 +2493,7 @@ static int _fp_exptmod_nct(fp_int * G, fp_int * X, fp_int * P, fp_int * Y)
/* G > P so we reduce it first */
err = fp_mod(G, P, &M[1]);
if (err != FP_OKAY) {
#ifndef WOLFSSL_NO_MALLOC
#if defined(WOLFSSL_SMALL_STACK) && !defined(WOLFSSL_NO_MALLOC)
XFREE(M, NULL, DYNAMIC_TYPE_BIGINT);
#endif
return err;
Expand All @@ -2503,7 +2503,7 @@ static int _fp_exptmod_nct(fp_int * G, fp_int * X, fp_int * P, fp_int * Y)
}
err = fp_mulmod (&M[1], res, P, &M[1]);
if (err != FP_OKAY) {
#ifndef WOLFSSL_NO_MALLOC
#if defined(WOLFSSL_SMALL_STACK) && !defined(WOLFSSL_NO_MALLOC)
XFREE(M, NULL, DYNAMIC_TYPE_BIGINT);
#endif
return err;
Expand All @@ -2516,14 +2516,14 @@ static int _fp_exptmod_nct(fp_int * G, fp_int * X, fp_int * P, fp_int * Y)
err = fp_sqr (&M[(word32)(1 << (winsize - 1))],
&M[(word32)(1 << (winsize - 1))]);
if (err != FP_OKAY) {
#ifndef WOLFSSL_NO_MALLOC
#if defined(WOLFSSL_SMALL_STACK) && !defined(WOLFSSL_NO_MALLOC)
XFREE(M, NULL, DYNAMIC_TYPE_BIGINT);
#endif
return err;
}
err = fp_montgomery_reduce_ex(&M[(word32)(1 << (winsize - 1))], P, mp, 0);
if (err != FP_OKAY) {
#ifndef WOLFSSL_NO_MALLOC
#if defined(WOLFSSL_SMALL_STACK) && !defined(WOLFSSL_NO_MALLOC)
XFREE(M, NULL, DYNAMIC_TYPE_BIGINT);
#endif
return err;
Expand All @@ -2534,14 +2534,14 @@ static int _fp_exptmod_nct(fp_int * G, fp_int * X, fp_int * P, fp_int * Y)
for (x = (1 << (winsize - 1)) + 1; x < (1 << winsize); x++) {
err = fp_mul(&M[x - 1], &M[1], &M[x]);
if (err != FP_OKAY) {
#ifndef WOLFSSL_NO_MALLOC
#if defined(WOLFSSL_SMALL_STACK) && !defined(WOLFSSL_NO_MALLOC)
XFREE(M, NULL, DYNAMIC_TYPE_BIGINT);
#endif
return err;
}
err = fp_montgomery_reduce_ex(&M[x], P, mp, 0);
if (err != FP_OKAY) {
#ifndef WOLFSSL_NO_MALLOC
#if defined(WOLFSSL_SMALL_STACK) && !defined(WOLFSSL_NO_MALLOC)
XFREE(M, NULL, DYNAMIC_TYPE_BIGINT);
#endif
return err;
Expand Down Expand Up @@ -2585,14 +2585,14 @@ static int _fp_exptmod_nct(fp_int * G, fp_int * X, fp_int * P, fp_int * Y)
if (mode == 1 && y == 0) {
err = fp_sqr(res, res);
if (err != FP_OKAY) {
#ifndef WOLFSSL_NO_MALLOC
#if defined(WOLFSSL_SMALL_STACK) && !defined(WOLFSSL_NO_MALLOC)
XFREE(M, NULL, DYNAMIC_TYPE_BIGINT);
#endif
return err;
}
err = fp_montgomery_reduce_ex(res, P, mp, 0);
if (err != FP_OKAY) {
#ifndef WOLFSSL_NO_MALLOC
#if defined(WOLFSSL_SMALL_STACK) && !defined(WOLFSSL_NO_MALLOC)
XFREE(M, NULL, DYNAMIC_TYPE_BIGINT);
#endif
return err;
Expand All @@ -2610,14 +2610,14 @@ static int _fp_exptmod_nct(fp_int * G, fp_int * X, fp_int * P, fp_int * Y)
for (x = 0; x < winsize; x++) {
err = fp_sqr(res, res);
if (err != FP_OKAY) {
#ifndef WOLFSSL_NO_MALLOC
#if defined(WOLFSSL_SMALL_STACK) && !defined(WOLFSSL_NO_MALLOC)
XFREE(M, NULL, DYNAMIC_TYPE_BIGINT);
#endif
return err;
}
err = fp_montgomery_reduce_ex(res, P, mp, 0);
if (err != FP_OKAY) {
#ifndef WOLFSSL_NO_MALLOC
#if defined(WOLFSSL_SMALL_STACK) && !defined(WOLFSSL_NO_MALLOC)
XFREE(M, NULL, DYNAMIC_TYPE_BIGINT);
#endif
return err;
Expand All @@ -2627,14 +2627,14 @@ static int _fp_exptmod_nct(fp_int * G, fp_int * X, fp_int * P, fp_int * Y)
/* then multiply */
err = fp_mul(res, &M[bitbuf], res);
if (err != FP_OKAY) {
#ifndef WOLFSSL_NO_MALLOC
#if defined(WOLFSSL_SMALL_STACK) && !defined(WOLFSSL_NO_MALLOC)
XFREE(M, NULL, DYNAMIC_TYPE_BIGINT);
#endif
return err;
}
err = fp_montgomery_reduce_ex(res, P, mp, 0);
if (err != FP_OKAY) {
#ifndef WOLFSSL_NO_MALLOC
#if defined(WOLFSSL_SMALL_STACK) && !defined(WOLFSSL_NO_MALLOC)
XFREE(M, NULL, DYNAMIC_TYPE_BIGINT);
#endif
return err;
Expand All @@ -2653,14 +2653,14 @@ static int _fp_exptmod_nct(fp_int * G, fp_int * X, fp_int * P, fp_int * Y)
for (x = 0; x < bitcpy; x++) {
err = fp_sqr(res, res);
if (err != FP_OKAY) {
#ifndef WOLFSSL_NO_MALLOC
#if defined(WOLFSSL_SMALL_STACK) && !defined(WOLFSSL_NO_MALLOC)
XFREE(M, NULL, DYNAMIC_TYPE_BIGINT);
#endif
return err;
}
err = fp_montgomery_reduce_ex(res, P, mp, 0);
if (err != FP_OKAY) {
#ifndef WOLFSSL_NO_MALLOC
#if defined(WOLFSSL_SMALL_STACK) && !defined(WOLFSSL_NO_MALLOC)
XFREE(M, NULL, DYNAMIC_TYPE_BIGINT);
#endif
return err;
Expand All @@ -2672,14 +2672,14 @@ static int _fp_exptmod_nct(fp_int * G, fp_int * X, fp_int * P, fp_int * Y)
/* then multiply */
err = fp_mul(res, &M[1], res);
if (err != FP_OKAY) {
#ifndef WOLFSSL_NO_MALLOC
#if defined(WOLFSSL_SMALL_STACK) && !defined(WOLFSSL_NO_MALLOC)
XFREE(M, NULL, DYNAMIC_TYPE_BIGINT);
#endif
return err;
}
err = fp_montgomery_reduce_ex(res, P, mp, 0);
if (err != FP_OKAY) {
#ifndef WOLFSSL_NO_MALLOC
#if defined(WOLFSSL_SMALL_STACK) && !defined(WOLFSSL_NO_MALLOC)
XFREE(M, NULL, DYNAMIC_TYPE_BIGINT);
#endif
return err;
Expand All @@ -2699,7 +2699,7 @@ static int _fp_exptmod_nct(fp_int * G, fp_int * X, fp_int * P, fp_int * Y)
/* swap res with Y */
fp_copy (res, Y);

#ifndef WOLFSSL_NO_MALLOC
#if defined(WOLFSSL_SMALL_STACK) && !defined(WOLFSSL_NO_MALLOC)
XFREE(M, NULL, DYNAMIC_TYPE_BIGINT);
#endif
return err;
Expand Down

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